File: csh.1

package info (click to toggle)
csh 20110502-2
  • links: PTS
  • area: main
  • in suites: wheezy
  • size: 1,104 kB
  • sloc: ansic: 11,984; makefile: 62; sh: 16
file content (2804 lines) | stat: -rw-r--r-- 70,418 bytes parent folder | download | duplicates (5)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
.\"	$OpenBSD: csh.1,v 1.65 2011/05/02 11:14:11 jmc Exp $
.\"	$NetBSD: csh.1,v 1.10 1995/03/21 09:02:35 cgd Exp $
.\"
.\" Copyright (c) 1980, 1990, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"	@(#)csh.1	8.2 (Berkeley) 1/21/94
.\"
.Dd $Mdocdate: May 2 2011 $
.Dt CSH 1
.Os
.Sh NAME
.Nm csh
.Nd a shell (command interpreter) with C-like syntax
.Sh SYNOPSIS
.Nm csh
.Op Fl bcefimnstVvXx
.Op Ar argument ...
.Nm csh
.Op Fl l
.Sh DESCRIPTION
.Nm
is a command language interpreter
incorporating a history mechanism (see
.Sx History substitutions ) ,
job control facilities (see
.Sx Jobs ) ,
interactive file name
and user name completion (see
.Sx File name completion ) ,
and a C-like syntax.
It is used both as an interactive
login shell and a shell script command processor.
.Ss Argument list processing
If the first argument (argument 0) to the shell is a dash
.Pq Sq \- ,
then this is a login shell.
A login shell also can be specified by invoking the shell with the
.Fl l
flag as the only argument.
.Pp
The rest of the flag arguments are interpreted as follows:
.Bl -tag -width 5n
.It Fl b
This flag forces a
.Dq break
from option processing, causing any further
shell arguments to be treated as non-option arguments.
The remaining arguments will not be interpreted as shell options.
This may be used to pass options to a shell script without confusion
or possible subterfuge.
The shell will not run a set-user-ID script without this option.
.It Fl c
Commands are read from the (single) following argument which must
be present.
Any remaining arguments are placed in
.Ar argv .
.It Fl e
The shell exits if any invoked command terminates abnormally
or yields a non-zero exit status.
.It Fl f
The shell will start faster, because it will neither search for nor
execute commands from the file
.Pa \&.cshrc
in the invoker's home directory.
Note: if the environment variable
.Ev HOME
is not set, fast startup is the default.
.It Fl i
The shell is interactive and prompts for its top-level input,
even if it appears not to be a terminal.
Shells are interactive without this option if their inputs
and outputs are terminals.
.It Fl l
The shell is a login shell (only applicable if
.Fl l
is the only flag specified).
.It Fl m
Read
.Pa \&.cshrc ,
regardless of its owner and group.
This option is dangerous and should only be used by
.Xr su 1 .
.It Fl n
Commands are parsed, but not executed.
This aids in syntactic checking of shell scripts.
When used interactively, the
shell can be terminated by pressing control-D (end-of-file character), since
.Ic exit
will not work.
.It Fl s
Command input is taken from the standard input.
.It Fl t
A single line of input is read and executed.
A backslash
.Pq Ql \e
may be used to escape the newline at the end of this
line and continue onto another line.
.It Fl V
Causes the
.Va verbose
variable to be set even before
.Pa .cshrc
is executed.
.It Fl v
Causes the
.Va verbose
variable to be set, with the effect
that command input is echoed after history substitution.
.It Fl X
Causes the
.Va echo
variable to be set even before
.Pa .cshrc
is executed.
.It Fl x
Causes the
.Va echo
variable to be set, so that commands are echoed immediately before execution.
.El
.Pp
After processing of flag arguments, if arguments remain but none of the
.Fl c ,
.Fl i ,
.Fl s ,
or
.Fl t
options were given, the first argument is taken as the name of a file of
commands to be executed.
The shell opens this file, and saves its name for possible resubstitution
by
.Sq $0 .
Since many systems use either the standard version 6 or version 7 shells
whose shell scripts are not compatible with this shell, the shell will
execute such a
.Dq standard
shell if the first character of a script
is not a hash mark
.Pq Ql # ;
i.e., if the script does not start with a comment.
Remaining arguments initialize the variable
.Va argv .
.Pp
An instance of
.Nm
begins by executing commands from the file
.Pa /etc/csh.cshrc
and,
if this is a login shell,
.Pa \&/etc/csh.login .
It then executes
commands from
.Pa \&.cshrc
in the home directory of the invoker,
and, if this is a login shell, the file
.Pa \&.login
in the same location.
It is typical for users on
.Tn CRT Ns s
to put the command
.Ic stty crt
in their
.Pa \&.login
file, and to also invoke
.Xr tset 1
there.
.Pp
In the normal case, the shell will begin reading commands from the
terminal, prompting with
.Sq %\ .
Processing of arguments and the use of the shell to process files
containing command scripts will be described later.
.Pp
The shell repeatedly performs the following actions:
a line of command input is read and broken into
.Dq words .
This sequence of words is placed on the command history list and parsed.
Finally each command in the current line is executed.
.Pp
When a login shell terminates it executes commands from the files
.Pa .logout
in the user's home directory and
.Pa /etc/csh.logout .
.Ss Lexical structure
The shell splits input lines into words at blanks and tabs with the
following exceptions.
The characters
.Ql & ,
.Ql | ,
.Ql \&; ,
.Ql < ,
.Ql > ,
.Ql \&( ,
and
.Ql \&)
form separate words.
If doubled in
.Ql && ,
.Ql || ,
.Ql << ,
or
.Ql >> ,
these pairs form single words.
These parser metacharacters may be made part of other words, or have their
special meaning prevented, by preceding them with a backslash
.Pq Ql \e .
A newline preceded by a
.Ql \e
is equivalent to a blank.
.Pp
Strings enclosed in matched pairs of quotations,
.Ql ' ,
.Ql ` ,
or
.Ql \&" ,
form parts of a word; metacharacters in these strings, including blanks
and tabs, do not form separate words.
These quotations have semantics to be described later.
Within pairs of
.Ql '
or
.Ql \&"
characters, a newline preceded by a
.Ql \e
gives
a true newline character.
.Pp
When the shell's input is not a terminal,
the character
.Ql #
introduces a comment that continues to the end of the
input line.
This special meaning is prevented when preceded by
.Ql \e
and in quotations using
.Ql ` ,
.Ql ' ,
and
.Ql \&" .
.Ss Commands
A simple command is a sequence of words, the first of which
specifies the command to be executed.
A simple command or
a sequence of simple commands separated by
.Ql |
characters forms a pipeline.
The output of each command in a pipeline is connected to the input of the next.
Sequences of pipelines may be separated by
.Ql \&; ,
and are then executed sequentially.
A sequence of pipelines may be executed without immediately
waiting for it to terminate by following it with a
.Ql & .
.Pp
Any of the above may be placed in
.Ql \&(
.Ql \&)
to form a simple command (that
may be a component of a pipeline, for example).
It is also possible to separate pipelines with
.Ql ||
or
.Ql &&
showing,
as in the C language,
that the second is to be executed only if the first fails or succeeds,
respectively.
(See
.Em Expressions . )
.Ss Jobs
The shell associates a
.Em job
with each pipeline.
It keeps a table of current jobs, printed by the
.Ic jobs
command, and assigns them small integer numbers.
When a job is started asynchronously with
.Ql & ,
the shell prints a line that looks
like:
.Bd -filled -offset indent
.Op 1
1234
.Ed
.Pp
showing that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process ID was 1234.
.Pp
If you are running a job and wish to do something else you may hit
.Ic ^Z
(control-Z), which sends a
.Dv SIGSTOP
signal to the current job.
The shell will then normally show that the job has been
.Dq Stopped ,
and print another prompt.
You can then manipulate the state of this job, putting it in the
.Em background
with the
.Ic bg
command, or run some other
commands and eventually bring the job back into the
.Em foreground
with the
.Ic fg
command.
A
.Ic ^Z
takes effect immediately and
is like an interrupt in that pending output and unread input are discarded
when it is typed.
There is another special key
.Ic ^Y
that does not generate a
.Dv SIGSTOP
signal until a program attempts to
.Xr read 2
it.
This request can usefully be typed ahead when you have prepared some commands
for a job that you wish to stop after it has read them.
.Pp
A job being run in the background will stop if it tries to read
from the terminal.
Background jobs are normally allowed to produce output,
but this can be disabled by giving the command
.Ic stty tostop .
If you set this
tty option, then background jobs will stop when they try to produce
output like they do when they try to read input.
.Pp
There are several ways to refer to jobs in the shell.
The character
.Ql %
introduces a job name.
If you wish to refer to job number 1, you can name it as
.Ql %1 .
Just naming a job brings it to the foreground; thus
.Ic %1
is a synonym for
.Ic fg %1 ,
bringing job number 1 back into the foreground.
Similarly, saying
.Ic %1 &
resumes job number 1 in the background.
Jobs can also be named by prefixes of the string typed in to start them,
if these prefixes are unambiguous; thus
.Ic %ex
would normally restart a suspended
.Xr ex 1
job, if there were only one suspended job whose name began with
the string
.Qq ex .
It is also possible to say
.Ic %?string ,
which specifies a job whose text contains
.Ar string ,
if there is only one such job.
.Pp
The shell maintains a notion of the current and previous jobs.
In output about jobs, the current job is marked with a
.Ql +
and the previous job with a
.Ql \- .
The abbreviation
.Ql %+
refers to the current job and
.Ql %\-
refers to the previous job.
For close analogy with the syntax of the
.Ic history
mechanism (described below),
.Ql %%
is also a synonym for the current job.
.Pp
The job control mechanism requires that the
.Xr stty 1
option
.Ic new
be set.
It is an artifact from a
.Em new
implementation
of the
tty driver that allows generation of interrupt characters from
the keyboard to tell jobs to stop.
See
.Xr stty 1
for details
on setting options in the new tty driver.
.Ss Status reporting
The shell learns immediately whenever a process changes state.
It normally informs you whenever a job becomes blocked so that
no further progress is possible, but only just before it prints
a prompt.
This is done so that it does not otherwise disturb your work.
If, however, you set the shell variable
.Va notify ,
the shell will notify you immediately of changes of status in background
jobs.
There is also a shell command
.Ic notify
that marks a single process so that its status changes will be immediately
reported.
By default
.Ic notify
marks the current process;
simply say
.Ic notify
after starting a background job to mark it.
.Pp
When you try to leave the shell while jobs are stopped, you will
be warned that
.Dq You have stopped jobs .
You may use the
.Ic jobs
command to see what they are.
If you try to exit again immediately,
the shell will not warn you a second time, and the suspended
jobs will be terminated.
.Ss File name completion
When the file name completion feature is enabled by setting
the shell variable
.Va filec
(see
.Ic set ) ,
.Nm
will
interactively complete file names and user names from unique
prefixes when they are input from the terminal followed by
the escape character (the escape key, or control-[).
For example,
if the current directory looks like
.Bd -literal -offset indent
DSC.OLD  bin      cmd      lib      xmpl.c
DSC.NEW  chaosnet cmtest   mail     xmpl.o
bench    class    dev      mbox     xmpl.out
.Ed
.Pp
and the input is
.Pp
.Dl % vi ch<escape>
.Pp
.Nm
will complete the prefix
.Dq ch
to the only matching file name
.Dq chaosnet ,
changing the input line to
.Pp
.Dl % vi chaosnet
.Pp
However, given
.Pp
.Dl % vi D<escape>
.Pp
.Nm
will only expand the input to
.Pp
.Dl % vi DSC.
.Pp
and will sound the terminal bell to indicate that the expansion is
incomplete, since there are two file names matching the prefix
.Ql D .
.Pp
If a partial file name is followed by the end-of-file character
(usually control-D), then, instead of completing the name,
.Nm
will list all file names matching the prefix.
For example, the input
.Pp
.Dl % vi D<control-D>
.Pp
causes all files beginning with
.Ql D
to be listed:
.Pp
.Dl DSC.NEW	DSC.OLD
.Pp
while the input line remains unchanged.
.Pp
The same system of escape and end-of-file can also be used to
expand partial user names, if the word to be completed
(or listed) begins with the tilde character
.Pq Ql ~ .
For example, typing
.Pp
.Dl cd ~ro<escape>
.Pp
may produce the expansion
.Pp
.Dl cd ~root
.Pp
The use of the terminal bell to signal errors or multiple matches
can be inhibited by setting the variable
.Va nobeep .
.Pp
Normally, all files in the particular directory are candidates
for name completion.
Files with certain suffixes can be excluded
from consideration by setting the variable
.Va fignore
to the
list of suffixes to be ignored.
Thus, if
.Va fignore
is set by
the command
.Pp
.Dl % set fignore = (.o .out)
.Pp
then typing
.Pp
.Dl % vi x<escape>
.Pp
would result in the completion to
.Pp
.Dl % vi xmpl.c
.Pp
ignoring the files
.Qq xmpl.o
and
.Qq xmpl.out .
However, if the only completion possible requires not ignoring these
suffixes, then they are not ignored.
In addition,
.Va fignore
does not affect the listing of file names by control-D.
All files are listed regardless of their suffixes.
.Ss Substitutions
We now describe the various transformations the shell performs on the
input in the order in which they occur.
.Ss History substitutions
History substitutions place words from previous command input as portions
of new commands, making it easy to repeat commands, repeat arguments
of a previous command in the current command, or fix spelling mistakes
in the previous command with little typing and a high degree of confidence.
History substitutions begin with the character
.Ql \&!
and may begin
.Em anywhere
in the input stream (with the proviso that they do
.Em not
nest).
This
.Ql \&!
may be preceded by a
.Ql \e
to prevent its special meaning; for
convenience, a
.Ql \&!
character is passed unchanged when it is followed by a blank,
tab, newline,
.Ql =
or
.Ql \&( .
(History substitutions also occur when an input line begins with
.Ql ^ .
This special abbreviation will be described later.)
Any input line that contains history substitution is echoed on the terminal
before it is executed as it would have been typed without history substitution.
.Pp
Commands input from the terminal that consist of one or more words
are saved on the history list.
The history substitutions reintroduce sequences of words from these
saved commands into the input stream.
The size of the history list is controlled by the
.Va history
variable; the previous command is always retained,
regardless of the value of the history variable.
Commands are numbered sequentially from 1.
.Pp
For definiteness, consider the following output from the
.Ic history
command:
.Bd -literal -offset indent
09  write michael
10  ex write.c
11  cat oldwrite.c
12  diff *write.c
.Ed
.Pp
The commands are shown with their event numbers.
It is not usually necessary to use event numbers, but the current event
number can be made part of the prompt by placing a
.Ql \&!
in the prompt string.
.Pp
With the current event 13 we can refer to previous events by event
number
.Ql !11 ,
relatively as in
.Ql !\-2
(referring to the same event),
by a prefix of a command word
as in
.Ql !d
for event 12 or
.Ql !wri
for event 9, or by a string contained in
a word in the command as in
.Ql !?mic?
also referring to event 9.
These forms, without further change, simply reintroduce the words
of the specified events, each separated by a single blank.
As a special case,
.Ql !!
refers to the previous command; thus
.Ql !!
alone is a
.Em redo .
.Pp
To select words from an event we can follow the event specification by
a
.Ql \&:
and a designator for the desired words.
The words of an input line are numbered from 0,
the first (usually command) word being 0, the second word (first argument)
being 1, etc.
The basic word designators are:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It \&0
first (command) word
.It Ar n
.Ar n Ns 'th
argument
.It ^
first argument; i.e.,
.Ql 1
.It $
last argument
.It %
word matched by (immediately preceding)
.No \&? Ns Ar s Ns ?\&
search
.It Ar \&x\-y
range of words
.It Ar \&\-y
abbreviates
.Ql \&0\-y
.It *
abbreviates
.Ql ^\-$ ,
or nothing if only 1 word in event
.It Ar x*
abbreviates
.Ql x\-$
.It Ar x\-
like
.Ql x*
but omitting word
.Ql $
.El
.Pp
The
.Ql \&:
separating the event specification from the word designator
can be omitted if the argument selector begins with a
.Ql ^ ,
.Ql $ ,
.Ql * ,
.Ql \- ,
or
.Ql % .
After the optional word designator,
a sequence of modifiers can be placed, each preceded by a
.Ql \&: .
The following modifiers are defined:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It h
Remove a trailing pathname component, leaving the head.
.It r
Remove a trailing
.Ql .xxx
component, leaving the root name.
.It e
Remove all but the extension
.Ql .xxx
part.
.It s Ns Ar /l/r/
Substitute
.Ar l
for
.Ar r .
.It t
Remove all leading pathname components, leaving the tail.
.It \&&
Repeat the previous substitution.
.It g
Apply the change once on each word, prefixing the above; e.g.,
.Ql g& .
.It a
Apply the change as many times as possible on a single word, prefixing
the above.
It can be used together with
.Ql g
to apply a substitution globally.
.It p
Print the new command line but do not execute it.
.It q
Quote the substituted words, preventing further substitutions.
.It x
Like
.Ql q ,
but break into words at blanks, tabs, and newlines.
.El
.Pp
Unless preceded by a
.Ql g
the change is applied only to the first
modifiable word.
With substitutions, it is an error for no word to be applicable.
.Pp
The left-hand side of substitutions are not regular expressions in the sense
of the editors, but instead strings.
Any character may be used as the delimiter in place of
.Ql / ;
a
.Ql \e
quotes the delimiter into the
.Ar l  " "
and
.Ar r  " "
strings.
The character
.Ql &
in the right-hand side is replaced by the text from
the left.
A
.Ql \e
also quotes
.Ql & .
A
.Dv NULL
.Ar l
.Pq Ql //
uses the previous string either from an
.Ar l
or from a
contextual scan string
.Ar s
in
.Ql !? Ns Ar s Ns \e? .
The trailing delimiter in the substitution may be omitted if a newline
follows immediately as may the trailing
.Ql \&?
in a contextual scan.
.Pp
A history reference may be given without an event specification; e.g.,
.Ql !$ .
Here, the reference is to the previous command unless a previous
history reference occurred on the same line in which case this form repeats
the previous reference.
Thus
.Dq !?foo?^ !$
gives the first and last arguments
from the command matching
.Dq ?foo? .
.Pp
A special abbreviation of a history reference occurs when the first
non-blank character of an input line is a
.Ql ^ .
This is equivalent to
.Dq !:s^
providing a convenient shorthand for substitutions
on the text of the previous line.
Thus
.Ic ^lb^lib
fixes the spelling of
.Dq lib
in the previous command.
Finally, a history substitution may be surrounded with
.Ql {
and
.Ql }
if necessary to insulate it from the characters that follow.
Thus, after
.Ic ls -ld ~paul
we might do
.Ic !{l}a
to do
.Ic ls -ld ~paula ,
while
.Ic !la
would look for a command starting with
.Dq la .
.Ss Quotations with \' and \&"
The quotation of strings by
.Ql '
and
.Ql \&"
can be used
to prevent all or some of the remaining substitutions.
Strings enclosed in
.Ql '
are prevented from any further interpretation.
Strings enclosed in
.Ql \&"
may be expanded as described below.
.Pp
In both cases the resulting text becomes (all or part of) a single word;
only in one special case (see
.Em Command Substitution
below) does a
.Ql \&"
quoted string yield parts of more than one word;
.Ql '
quoted strings never do.
.Ss Alias substitution
The shell maintains a list of aliases that can be established, displayed
and modified by the
.Ic alias
and
.Ic unalias
commands.
After a command line is scanned, it is parsed into distinct commands and
the first word of each command, left-to-right, is checked to see if it
has an alias.
If it does, then the text that is the alias for that command is reread
with the history mechanism available
as though that command were the previous input line.
The resulting words replace the
command and argument list.
If no reference is made to the history list, then the argument list is
left unchanged.
.Pp
Thus if the alias for
.Dq ls
is
.Dq ls \-l ,
the command
.Ic ls /usr
would map to
.Ic ls \-l /usr ,
the argument list here being undisturbed.
Similarly, if the alias for
.Dq lookup
was
.Dq grep !^ /etc/passwd
then
.Ic lookup bill
would map to
.Ic grep bill /etc/passwd .
.Pp
If an alias is found, the word transformation of the input text
is performed and the aliasing process begins again on the reformed input line.
Looping is prevented if the first word of the new text is the same as the old
by flagging it to prevent further aliasing.
Other loops are detected and cause an error.
.Pp
Note that the mechanism allows aliases to introduce parser metasyntax.
Thus, we can
.Ic alias print 'pr \e!* \&| lpr'
to make a command that
.Ic pr Ns 's
its arguments to the line printer.
.Ss Variable substitution
The shell maintains a set of variables, each of which has as value a list
of zero or more words.
Some of these variables are set by the shell or referred to by it.
For instance, the
.Va argv
variable is an image of the shell's argument list, and words of this
variable's value are referred to in special ways.
.Pp
The values of variables may be displayed and changed by using the
.Ic set
and
.Ic unset
commands.
Of the variables referred to by the shell a number are toggles;
the shell does not care what their value is,
only whether they are set or not.
For instance, the
.Va verbose
variable is a toggle that causes command input to be echoed.
The setting of this variable results from the
.Fl v
command-line option.
.Pp
Other operations treat variables numerically.
The
.Ic @
command permits numeric calculations to be performed and the result
assigned to a variable.
Variable values are, however, always represented as (zero or more) strings.
For the purposes of numeric operations, the null string is considered to be
zero, and the second and additional words of multiword values are ignored.
.Pp
After the input line is aliased and parsed, and before each command
is executed, variable substitution
is performed, keyed by
.Ql $
characters.
This expansion can be prevented by preceding the
.Ql $
with a
.Ql \e
except
within double quotes (`"'), where it
.Em always
occurs, and within single quotes (`''), where it
.Em never
occurs.
Strings quoted by backticks
.Pq ` `
are interpreted later (see
.Sx Command substitution
below), so
.Ql $
substitution does not occur there until later, if at all.
A
.Ql $
is passed unchanged if followed by a blank, tab, or end-of-line.
.Pp
Input/output redirections are recognized before variable expansion,
and are variable expanded separately.
Otherwise, the command name and entire argument list are expanded together.
It is thus possible for the first (command) word (to this point) to generate
more than one word, the first of which becomes the command name,
and the rest of which become arguments.
.Pp
Unless enclosed in
.Ql \&"
or given the
.Ql :q
modifier, the results of variable
substitution may eventually be command and filename substituted.
Within
.Ql \&" ,
a variable whose value consists of multiple words expands to
(a portion of) a single word, with the words of the variable's value
separated by blanks.
When the
.Ql :q
modifier is applied to a substitution
the variable will expand to multiple words with each word separated
by a blank and quoted to prevent later command or filename substitution.
.Pp
The following metasequences are provided for introducing variable values into
the shell input.
Except as noted, it is an error to reference a variable that is not set.
.Pp
.Bl -tag -width Ds -compact -offset indent
.It $name
.It ${name}
Are replaced by the words of the value of variable
.Ar name ,
each separated by a blank.
Braces insulate
.Ar name
from following characters that would otherwise be part of it.
Shell variables have names consisting of up to 20 letters and digits
starting with a letter.
The underscore character is considered a letter.
If
.Ar name
is not a shell variable, but is set in the environment, then
that value is returned (but
.Ql \&:
modifiers and the other forms
given below are not available here).
.It $name Ns Op selector
.It ${name Ns [ selector ] Ns }
May be used to select only some of the words from the value of
.Ar name .
The selector is subjected to
.Ql $
substitution and may consist of a single
number or two numbers separated by a
.Ql \- .
The first word of a variable's value is numbered
.Ql 1 .
If the first number of a range is omitted it defaults to
.Ql 1 .
If the last number of a range is omitted it defaults to
.Ql $#name .
The selector
.Ql *
selects all words.
It is not an error for a range to be empty if the second argument is omitted
or in range.
.It $#name
.It ${#name}
Gives the number of words in the variable.
This is useful for later use in a
.Dq $argv[selector] .
.It $0
Substitutes the name of the file from which command input is being read.
An error occurs if the name is not known.
.It $number
.It ${number}
Equivalent to
.Dq $argv[number] .
.It $*
Equivalent to
.Dq $argv[*] .
.El
.Pp
The modifiers
.Ql :e ,
.Ql :h ,
.Ql :t ,
.Ql :r ,
.Ql :q ,
and
.Ql :x
may be applied to
the substitutions above as may
.Ql :gh ,
.Ql :gt ,
and
.Ql :gr .
If braces
.Ql {
.Ql }
appear in the command form then the modifiers
must appear within the braces.
The current implementation allows only one
.Ql \&:
modifier on each
.Ql $
expansion.
.Pp
The following substitutions may not be modified with
.Ql \&:
modifiers.
.Bl -tag -width Ds -compact -offset indent
.It $?name
.It ${?name}
Substitutes the string
.Dq 1
if name is set,
.Dq 0
if it is not.
.It $?0
Substitutes
.Ql 1
if the current input filename is known,
.Ql 0
if it is not.
.It \&$\&$\&
Substitute the (decimal) process number of the (parent) shell.
Do
.Em NOT
use this mechanism for generating temporary file names; see
.Xr mktemp 1
instead.
.It $!
Substitute the (decimal) process number of the last background process
started by this shell.
.It $<
Substitutes a line from the standard
input, with no further interpretation.
It can be used to read from the keyboard in a shell script.
.El
.Ss Command and filename substitution
The remaining substitutions, command and filename substitution,
are applied selectively to the arguments of built-in commands.
By selectively, we mean that portions of expressions which are
not evaluated are not subjected to these expansions.
For commands that are not internal to the shell, the command
name is substituted separately from the argument list.
This occurs very late,
after input-output redirection is performed, and in a child
of the main shell.
.Ss Command substitution
Command substitution is shown by a command enclosed in
.Ql ` .
The output from such a command is normally broken into separate words
at blanks, tabs, and newlines, with null words being discarded;
this text then replaces the original string.
Within double quotes (`"'), only newlines force new words;
blanks and tabs are preserved.
.Pp
In any case, the single final newline does not force a new word.
Note that it is thus possible for a command substitution to yield
only part of a word, even if the command outputs a complete line.
.Ss Filename substitution
If a word contains any of the characters
.Ql * ,
.Ql \&? ,
.Ql \&[ ,
or
.Ql { ,
or begins with the character
.Ql ~ ,
then that word is a candidate for
filename substitution, also known as
.Dq globbing .
This word is then regarded as a pattern, and replaced with an alphabetically
sorted list of file names that match the pattern.
In a list of words specifying filename substitution it is an error for
no pattern to match an existing file name, but it is not required
for each pattern to match.
Only the metacharacters
.Ql * ,
.Ql \&? ,
and
.Ql \&[
imply pattern matching,
the characters
.Ql ~
and
.Ql {
being more akin to abbreviations.
.Pp
In matching filenames, the character
.Ql \&.
at the beginning of a filename
or immediately following a
.Ql / ,
as well as the character
.Ql /
must be matched explicitly.
The character
.Ql *
matches any string of characters, including the null
string.
The character
.Ql \&?
matches any single character.
.Pp
The sequence
.Dq Op ...
matches any one of the characters enclosed.
Within
.Dq Op ... ,
a pair of characters separated by
.Ql \-
matches any character lexically between
the two (inclusive).
Within
.Dq Op ... ,
the name of a
.Em character class
enclosed in
.Sq [:
and
.Sq :]
stands for the list of all characters belonging to that class.
Supported character classes:
.Bl -column "xdigit" "xdigit" "xdigit" -offset indent
.It Li "alnum" Ta "cntrl" Ta "lower" Ta "space"
.It Li "alpha" Ta "digit" Ta "print" Ta "upper"
.It Li "blank" Ta "graph" Ta "punct" Ta "xdigit"
.El
.Pp
These match characters using the macros specified in
.Xr ctype 3 .
A character class may not be used as an endpoint of a range.
.Pp
The character
.Ql ~
at the beginning of a filename refers to home
directories.
Standing alone, i.e.,
.Ql ~ ,
it expands to the invoker's home directory as reflected
in the value of the variable
.Ar home .
When followed by a name consisting of letters, digits, and
.Ql \-
characters,
the shell searches for a user with that name and substitutes their
home directory; thus
.Dq ~ken
might expand to
.Dq /usr/ken
and
.Dq ~ken/chmach
to
.Dq /usr/ken/chmach .
If the character
.Ql ~
is followed by a character other than a letter or
.Ql / ,
or does not appear at the beginning of a word,
it is left undisturbed.
.Pp
The metanotation
.Dq a{b,c,d}e
is a shorthand for
.Dq abe ace ade .
Left to right order is preserved, with results of matches being sorted
separately at a low level to preserve this order.
This construct may be nested.
Thus,
.Dq ~source/s1/{oldls,ls}.c
expands to
.Dq /usr/source/s1/oldls.c /usr/source/s1/ls.c
without chance of error
if the home directory for
.Dq source
is
.Dq /usr/source .
Similarly
.Dq ../{memo,*box}
might expand to
.Dq ../memo ../box ../mbox .
(Note that
.Dq memo
was not sorted with the results of the match to
.Dq *box . )
As a special case
.Ql { ,
.Ql } ,
and
.Ql {}
are passed undisturbed.
.Ss Input/output
The standard input and the standard output of a command may be redirected
with the following syntax:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It < name
Open file
.Ar name
(which is first variable, command, and filename expanded) as the standard
input.
.It << word
Read the shell input up to a line that is identical to
.Ar word .
.Ar word
is not subjected to variable, command, or filename substitution,
and each input line is compared to
.Ar word
before any substitutions are done on the input line.
Unless a quoting
.Ql \e ,
.Ql \&" ,
.Ql '
or
.Ql `
appears in
.Ar word ,
variable and command substitution is performed on the intervening lines,
allowing
.Ql \e
to quote
.Ql $ ,
.Ql \e
and
.Ql ` .
Commands that are substituted have all blanks, tabs, and newlines
preserved, except for the final newline which is dropped.
The resultant text is placed in an anonymous temporary file that
is given to the command as its standard input.
.It > name
.It >! name
.It >& name
.It >&! name
The file
.Ar name
is used as the standard output.
If the file does not exist then it is created;
if the file exists, it is truncated; its previous contents are lost.
.Pp
If the variable
.Va noclobber
is set, then the file must not exist or be a character special file (e.g., a
terminal or
.Pa /dev/null )
or an error results.
This helps prevent accidental destruction of files.
Here, the
.Ql \&!
forms can be used to suppress this check.
.Pp
The forms involving
.Ql &
route the standard error output into the specified
file as well as the standard output.
.Ar name
is expanded in the same way as
.Ql <
input filenames are.
.It >> name
.It >>& name
.It >>! name
.It >>&! name
Uses file
.Ar name
as the standard output;
like
.Ql >
but places output at the end of the file.
If the variable
.Va noclobber
is set, then it is an error for the file not to exist unless
one of the
.Ql \&!
forms is given.
Otherwise similar to
.Ql > .
.El
.Pp
A command receives the environment in which the shell was
invoked as modified by the input-output parameters and
the presence of the command in a pipeline.
Thus, unlike some previous shells, commands run from a file of shell commands
have no access to the text of the commands by default;
instead they receive the original standard input of the shell.
The
.Ql <<
mechanism should be used to present inline data.
This permits shell command scripts to function as components of pipelines
and allows the shell to block read its input.
Note that the default standard input for a command run detached is
.Ar not
modified to be the empty file
.Pa /dev/null ;
instead the standard input
remains as the original standard input of the shell.
If this is a terminal
and if the process attempts to read from the terminal, then the process
will block and the user will be notified (see
.Sx Jobs
above).
.Pp
The standard error output may be directed through
a pipe with the standard output.
Simply use the form
.Ql |&
instead of just
.Ql | .
.Ss Expressions
Several of the built-in commands (to be described later)
take expressions, in which the operators are similar to those of C, with
the same precedence, but with the
.Em opposite grouping :
right to left.
These expressions appear in the
.Ic @ ,
.Ic exit ,
.Ic if ,
and
.Ic while
commands.
The following operators are available:
.Bd -ragged -offset indent
||  &&  | \*(ua  &  ==  !=  =~  !~  <=  >=
<  > <<  >>  +  \-  *  /  %  !  ~  (  )
.Ed
.Pp
Here the precedence increases to the right,
.Ql ==
.Ql !=
.Ql =~
and
.Ql !~ ,
.Ql <=
.Ql >=
.Ql <
and
.Ql > ,
.Ql <<
and
.Ql >> ,
.Ql +
and
.Ql \- ,
.Ql *
.Ql /
and
.Ql %
being, in groups, at the same level.
The
.Ql ==
.Ql !=
.Ql =~
and
.Ql !~
operators compare their arguments as strings;
all others operate on numbers.
The operators
.Ql =~
and
.Ql !~
are like
.Ql !=
and
.Ql ==
except that the right
hand side is a
.Ar pattern
(containing, e.g., *'s, ?'s, and instances of
.Dq [...] )
against which the left-hand operand is matched.
This reduces the need for use of the
.Ar switch
statement in shell scripts when all that is really needed is pattern matching.
.Pp
Strings that begin with
.Ql 0
are considered octal numbers.
Null or missing arguments are considered
.Ql 0 .
The results of all expressions are strings,
which represent decimal numbers.
It is important to note that no two components of an expression can appear
in the same word; except when adjacent to components of expressions that
are syntactically significant to the parser
.Po
.Ql & ,
.Ql | ,
.Ql < ,
.Ql > ,
.Ql \&( ,
and
.Ql \&)
.Pc ,
they should be surrounded by spaces.
.Pp
Also available in expressions as primitive operands are command executions
enclosed in
.Ql {
and
.Ql }
and file enquiries of the form
.Fl l
.Ar name
where
.Ic l
is one of:
.Bd -literal -offset indent
r	read access
w	write access
x	execute access
e	existence
o	ownership
z	zero size
f	plain file
d	directory
.Ed
.Pp
The specified name is command and filename expanded and then tested
to see if it has the specified relationship to the real user.
If the file does not exist or is inaccessible then all enquiries return
false, i.e.,
.Ql 0 .
Command executions succeed, returning true, i.e.,
.Ql 1 ,
if the command exits with status 0, otherwise they fail, returning
false, i.e.,
.Ql 0 .
If more detailed status information is required then the command
should be executed outside an expression and the variable
.Ar status
examined.
.Ss Control flow
The shell contains several commands that can be used to regulate the
flow of control in command files (shell scripts) and
(in limited but useful ways) from terminal input.
These commands all operate by forcing the shell to reread or skip in its
input and, because of the implementation, restrict the placement of some
of the commands.
.Pp
The
.Ic foreach ,
.Ic switch ,
and
.Ic while
statements, as well as the
.Ic if\-then\-else
form of the
.Ic if
statement require that the major keywords appear in a single simple command
on an input line as shown below.
.Pp
If the shell's input is not seekable,
the shell buffers up input whenever a loop is being read
and performs seeks in this internal buffer to accomplish the rereading
implied by the loop.
(To the extent that this allows, backward goto's will succeed on
non-seekable inputs.)
.Ss Built-in commands
Built-in commands are executed within the shell.
If a built-in command occurs as any component of a pipeline
except the last then it is executed in a sub-shell.
.Pp
.Bl -tag -width Ds -compact -offset indent
.It Ic alias
.It Ic alias Ar name
.It Ic alias Ar name wordlist
The first form prints all aliases.
The second form prints the alias for name.
The final form assigns the specified
.Ar wordlist
as the alias of
.Ar name ;
.Ar wordlist
is command and filename substituted.
.Ar name
is not allowed to be
.Dq alias
or
.Dq unalias .
.Pp
.It Ic alloc
Shows the amount of dynamic memory acquired, broken down into used and
free memory.
With an argument shows the number of free and used blocks in each size
category.
The categories start at size 8 and double at each step.
This command's output may vary across system types, since
systems other than the
.Tn VAX
may use a different memory allocator.
.Pp
.It Ic bg
.It Ic bg \&% Ns Ar job ...
Puts the current or specified jobs into the background, continuing them
if they were stopped.
.Pp
.It Ic break
Causes execution to resume after the
.Ic end
of the nearest enclosing
.Ic foreach
or
.Ic while .
The remaining commands on the current line are executed.
Multi-level breaks are thus possible by writing them all on one line.
.Pp
.It Ic breaksw
Causes a break from a
.Ic switch ,
resuming after the
.Ic endsw .
.Pp
.It Ic case Ar label :
A label in a
.Ic switch
statement as discussed below.
.Pp
.It Ic cd
.It Ic cd Ar name
.It Ic chdir
.It Ic chdir Ar name
Change the shell's working directory to directory
.Ar name .
If no argument is given then change to the home directory of the user.
If
.Ar name
is not found as a subdirectory of the current directory (and does not begin
with
.Ql / ,
.Ql ./
or
.Ql ../ ) ,
then each
component of the variable
.Va cdpath
is checked to see if it has a subdirectory
.Ar name .
Finally, if all else fails but
.Ar name
is a shell variable whose value begins with
.Ql / ,
then this
is tried to see if it is a directory.
.Pp
.It Ic continue
Continue execution of the nearest enclosing
.Ic while
or
.Ic foreach .
The rest of the commands on the current line are executed.
.Pp
.It Ic default :
Labels the default case in a
.Ic switch
statement.
The default should come after all
.Ic case
labels.
.Pp
.It Ic dirs
Prints the directory stack; the top of the stack is at the left,
the first directory in the stack being the current directory.
.Pp
.It Ic echo Ar wordlist
.It Ic echo Fl n Ar wordlist
The specified words are written to the shell's standard output, separated
by spaces, and terminated with a newline unless the
.Fl n
option is specified.
.Pp
.It Ic else
.It Ic end
.It Ic endif
.It Ic endsw
See the description of the
.Ic foreach ,
.Ic if ,
.Ic switch ,
and
.Ic while
statements below.
.Pp
.It Ic eval Ar arg ...
(As in
.Xr sh 1 . )
The arguments are read as input to the shell and the resulting
command(s) executed in the context of the current shell.
This is usually used to execute commands
generated as the result of command or variable substitution, since
parsing occurs before these substitutions.
See
.Xr tset 1
for an example of using
.Ic eval .
.Pp
.It Ic exec Ar command
The specified command is executed in place of the current shell.
.Pp
.It Ic exit
.It Ic exit ( Ar expr )
The shell exits either with the value of the
.Ic status
variable (first form) or with the value of the specified
.Ic expr
(second form).
.Pp
.It Ic fg
.It Ic fg % Ns Ar job ...
Brings the current or specified jobs into the foreground, continuing them if
they were stopped.
.Pp
.It Ic foreach Ar name ( Ar wordlist )
.It ...
.It Ic end
The variable
.Ar name
is successively set to each member of
.Ar wordlist
and the sequence of commands between this command and the matching
.Ic end
are executed.
(Both
.Ic foreach
and
.Ic end
must appear alone on separate lines.)
The built-in command
.Ic continue
may be used to continue the loop prematurely and the built-in
command
.Ic break
to terminate it prematurely.
When this command is read from the terminal, the loop is read once
prompting with
.Ql \&?
before any statements in the loop are executed.
If you make a mistake typing in a loop at the terminal you can rub it out.
.Pp
.It Ic glob Ar wordlist
Like
.Ic echo
but no
.Ql \e
escapes are recognized and words are delimited
by
.Tn NUL
characters in the output.
Useful for programs that wish to use the shell to filename expand a list
of words.
.Pp
.It Ic goto Ar word
The specified
.Ar word
is filename and command expanded to yield a string of the form
.Ql label .
The shell rewinds its input as much as possible
and searches for a line of the form
.Dq label: ,
possibly preceded by blanks or tabs.
Execution continues after the specified line.
.Pp
.It Ic hashstat
Print a statistics line showing how effective the internal hash
table has been at locating commands (and avoiding
.Ic exec Ns \'s ) .
An
.Ic exec
is attempted for each component of the
.Em path
where the hash function indicates a possible hit, and in each component
that does not begin with a
.Ql / .
.Pp
.It Ic history
.It Ic history Ar n
.It Ic history Fl h Ar n
.It Ic history Fl r Ar n
Displays the history event list; if
.Ar n
is given, only the
.Ar n
most recent events are printed.
The
.Fl h
option causes the history list to be printed without leading numbers.
This format produces files suitable for sourcing using the
.Fl h
option to
.Ic source .
The
.Fl r
option reverses the order of printout to be most recent first
instead of oldest first.
.Pp
.It Ic if ( Ar expr ) No command
If the specified expression evaluates to true, then the single
.Ar command
with arguments is executed.
Variable substitution on
.Ar command
happens early, at the same
time it does for the rest of the
.Ic if
command.
.Ar command
must be a simple command, not
a pipeline, a command list, or a parenthesized command list.
Input/output redirection occurs even if
.Ar expr
is false, i.e., when command is
.Em not
executed (this is a bug).
.Pp
.It Ic if ( Ar expr ) Ic then
.It ...
.It Ic else if ( Ar expr2 ) Ic then
.It ...
.It Ic else
.It ...
.It Ic endif
If the specified
.Ar expr
is true then the commands up to the first
.Ic else
are executed; otherwise if
.Ar expr2
is true then the commands up to the
second
.Ic else
are executed, etc.
Any number of
.Ic else-if
pairs are possible; only one
.Ic endif
is needed.
The
.Ic else
part is likewise optional.
(The words
.Ic else
and
.Ic endif
must appear at the beginning of input lines;
the
.Ic if
must appear alone on its input line or after an
.Ic else . )
.Pp
.It Ic jobs
.It Ic jobs Fl l
Lists the active jobs; the
.Fl l
option lists process IDs in addition to the normal information.
.Pp
.It Ic kill % Ns Ar job
.It Ic kill
.Op Fl s Ar signal_name
.Ar pid
.It Ic kill Fl sig Ar pid ...
.It Ic kill Fl l Op exit_status
Sends either the
.Dv SIGTERM
(terminate) signal or the
specified signal to the specified jobs or processes.
Signals are either given by number or by names (as given in
.Aq Pa signal.h ,
stripped of the prefix
.Dq SIG ) .
The signal names are listed by
.Dq kill \-l ;
if an
.Ar exit_status
is specified, only the corresponding signal name will be written.
There is no default; just saying
.Dq kill
does not
send a signal to the current job.
If the signal being sent is
.Dv SIGTERM
(terminate) or
.Dv SIGHUP
(hangup),
then the job or process will be sent a
.Dv SIGCONT
(continue) signal as well.
.Pp
.It Ic limit
.It Ic limit Ar resource
.It Ic limit Ar resource maximum-use
.It Ic limit Fl h
.It Ic limit Fl h Ar resource
.It Ic limit Fl h Ar resource maximum-use
Limits the consumption by the current process and each process
it creates to not individually exceed
.Ar maximum-use
on the
specified
.Ar resource .
If no
.Ar maximum-use
is given, then
the current limit is printed; if no
.Ar resource
is given, then
all limitations are given.
If the
.Fl h
flag is given, the hard limits are used instead of the current limits.
The hard limits impose a ceiling on the values of the current limits.
Only the superuser may raise the hard limits,
but a user may lower or raise the current limits within the legal range.
.Pp
Resources controllable currently include:
.Bl -tag -width coredumpsize
.It Ar cputime
the maximum number of CPU-seconds to be used by each process.
.It Ar filesize
the largest single file (in bytes) that can be created.
.It Ar datasize
the maximum growth of the data+stack region via
.Xr sbrk  2
beyond the end of the program text.
.It Ar stacksize
the maximum
size of the automatically-extended stack region.
.It Ar coredumpsize
the size of the largest core dump (in bytes) that will be created.
.It Ar memoryuse
the maximum size (in bytes) to which a process's resident set
size (RSS) may grow.
.It Ar memorylocked
The maximum size (in bytes) which a process may lock into memory using the
.Xr mlock 2
function.
.It Ar maxproc
The maximum number of simultaneous processes for this user ID.
.It Ar openfiles
The maximum number of simultaneous open files for this user ID.
.It Ar vmemoryuse
the maximum size (in bytes) to which a process's total size may grow.
.El
.Pp
The
.Ar maximum-use
may be given as a (floating point or integer)
number followed by a scale factor.
For all limits other than
.Ar cputime
the default scale is
.Ql k
or
.Dq kilobytes
(1024 bytes);
a scale factor of
.Ql m
or
.Dq megabytes
may also be used.
For
.Ar cputime
the default scale is
.Dq seconds ;
a scale factor of
.Ql m
for minutes
or
.Ql h
for hours, or a time of the form
.Dq mm:ss
giving minutes
and seconds also may be used.
.Pp
For both
.Ar resource
names and scale factors, unambiguous prefixes
of the names suffice.
.Pp
.It Ic login
Terminate a login shell, replacing it with an instance of
.Pa /usr/bin/login .
This is one way to log off, included for compatibility with
.Xr sh 1 .
.Pp
.It Ic logout
Terminate a login shell.
Especially useful if
.Va ignoreeof
is set.
.Pp
.It Ic nice
.It Ic nice Ar +number
.It Ic nice Ar command
.It Ic nice Ar +number command
The first form sets the
scheduling priority
for this shell to 4.
The second form sets the
priority
to the given
.Ar number .
The final two forms run command at priority 4 and
.Ar number
respectively.
The greater the number, the less
.Tn CPU
the process will get.
The superuser may specify negative priority by using
.Dq nice \-number ... .
.Ar command
is always executed in a sub-shell, and the restrictions
placed on commands in simple
.Ic if
statements apply.
.Pp
.It Ic nohup
.It Ic nohup Ar command
The first form can be used in shell scripts to cause hangups to be
ignored for the remainder of the script.
The second form causes the specified command to be run with hangups
ignored.
All processes detached with
.Ql &
are effectively
.Ic nohup Ns \'ed .
.Pp
.It Ic notify
.It Ic notify % Ns Ar job ...
Causes the shell to notify the user asynchronously when the status of the
current or specified jobs change; normally notification is presented
before a prompt.
This is automatic if the shell variable
.Va notify
is set.
.Pp
.It Ic onintr
.It Ic onintr Fl
.It Ic onintr Ar label
Control the action of the shell on interrupts.
The first form restores the default action of the shell on interrupts,
which is to terminate shell scripts or to return to the terminal command
input level.
The second form
.Ic onintr \-
causes all interrupts to be ignored.
The final form causes the shell to execute a
.Ic goto label
when
an interrupt is received or a child process terminates because
it was interrupted.
.Pp
In any case, if the shell is running detached and interrupts are
being ignored, all forms of
.Ic onintr
have no meaning and interrupts
continue to be ignored by the shell and all invoked commands.
Finally,
.Ic onintr
statements are ignored in the system startup files where interrupts
are disabled
.Pq Pa /etc/csh.cshrc , /etc/csh.login .
.Pp
.It Ic popd
.It Ic popd Ar +n
Pops the directory stack, returning to the new top directory.
With an argument
.Dq + Ns Ar n
discards the
.Ar n Ns \'th
entry in the stack.
The members of the directory stack are numbered from the top starting at 0.
.Pp
.It Ic pushd
.It Ic pushd Ar name
.It Ic pushd Ar +n
With no arguments,
.Ic pushd
exchanges the top two elements of the directory stack.
Given a
.Ar name
argument,
.Ic pushd
changes to the new directory (ala
.Ic cd )
and pushes the old current working directory
(as in
.Ic cwd )
onto the directory stack.
With a numeric argument,
.Ic pushd
rotates the
.Ar n Ns \'th
argument of the directory
stack around to be the top element and changes to it.
The members
of the directory stack are numbered from the top starting at 0.
.Pp
.It Ic rehash
Causes the internal hash table of the contents of the directories in
the
.Va path
variable to be recomputed.
This is needed if new commands are added to directories in the
.Ic path
while you are logged in.
This should only be necessary if you add
commands to one of your own directories, or if a systems programmer
changes the contents of a system directory.
.Pp
.It Ic repeat Ar count command
The specified
.Ar command ,
which is subject to the same restrictions
as the
.Ar command
in the one line
.Ic if
statement above,
is executed
.Ar count
times.
I/O redirections occur exactly once, even if
.Ar count
is 0.
.Pp
.It Ic set
.It Ic set Ar name
.It Ic set Ar name Ns =word
.It Ic set Ar name[index] Ns =word
.It Ic set Ar name Ns =(wordlist)
The first form of the command shows the value of all shell variables.
Variables that have other than a single word as their
value print as a parenthesized word list.
The second form sets
.Ar name
to the null string.
The third form sets
.Ar name
to the single
.Ar word .
The fourth form sets
the
.Ar index Ns 'th
component of
.Ar name
to
.Ar word ;
this component must already exist.
The final form sets
.Ar name
to the list of words in
.Ar wordlist .
The value is always command and filename expanded.
.Pp
These arguments may be repeated to set multiple values in a single set command.
Note however, that variable expansion happens for all arguments before any
setting occurs.
.Pp
.It Ic setenv
.It Ic setenv Ar name
.It Ic setenv Ar name value
The first form lists all current environment variables.
It is equivalent to
.Xr printenv 1 .
The last form sets the value of environment variable
.Ar name
to be
.Ar value ,
a single string.
The second form sets
.Ar name
to an empty string.
The most commonly used environment variables
.Ev USER ,
.Ev TERM ,
and
.Ev PATH
are automatically imported to and exported from the
.Nm
variables
.Ar user ,
.Ar term ,
and
.Ar path ;
there is no need to use
.Ic setenv
for these.
.Pp
.It Ic shift
.It Ic shift Ar variable
The members of
.Ic argv
are shifted to the left, discarding
.Ic argv Ns Bq 1 .
It is an error for
.Ic argv
not to be set or to have less than one word as value.
The second form performs the same function on the specified variable.
.Pp
.It Ic source Ar name
.It Ic source Fl h Ar name
The shell reads commands from
.Ar name .
.Ic source
commands may be nested; if they are nested too deeply the shell may
run out of file descriptors.
An error in a
.Ic source
at any level terminates all nested
.Ic source
commands.
Normally input during
.Ic source
commands is not placed on the history list;
the
.Fl h
option causes the commands to be placed on the
history list without being executed.
.Pp
.It Ic stop
.It Ic stop % Ns Ar job ...
Stops the current or specified jobs that are executing in the background.
.Pp
.It Ic suspend
Causes the shell to stop in its tracks, much as if it had been sent a stop
signal with
.Ic ^Z .
This is most often used to stop shells started by
.Xr su 1 .
.Pp
.It Ic switch ( Ar string )
.It Ic case Ar str1 :
.It \ \ \ \ \&...
.It Ic \ \ \ \ breaksw
.It \ \ \ \ \&...
.It Ic default :
.It \ \ \ \ \&...
.It Ic \ \ \ \ breaksw
.It Ic endsw
Each case label is successively matched against the specified
.Ar string ,
which is first command and filename expanded.
The file metacharacters
.Ql * ,
.Ql \&?
and
.Dq [...]
may be used in the case labels,
which are variable expanded.
If none of the labels match before the
.Dq default
label is found, then
the execution begins after the default label.
Each case label and the default label must appear at the beginning of a line.
The command
.Ic breaksw
causes execution to continue after the
.Ic endsw .
Otherwise control may fall through case labels and the default label as in C.
If no label matches and there is no default, execution continues after
the
.Ic endsw .
.Pp
.It Ic time
.It Ic time Ar command
With no argument, a summary of time used by this shell and its children
is printed.
If arguments are given
the specified simple command is timed and a time summary
as described under the
.Ic time
variable is printed.
If necessary, an extra shell is created to print the time
statistic when the command completes.
.Pp
.It Ic umask
.It Ic umask Ar value
The file creation mask is displayed (first form) or set to the specified
value (second form).
The mask is given in octal.
Common values for
the mask are 002 giving all access to the group and read and execute
access to others or 022 giving all access except write access for
users in the group or others.
.Pp
.It Ic unalias Ar pattern
All aliases whose names match the specified pattern are discarded.
Thus all aliases are removed by
.Ic unalias * .
It is not an error for nothing to be
.Ic unalias Ns ed.
.Pp
.It Ic unhash
Use of the internal hash table to speed location of executed programs
is disabled.
.Pp
.It Ic unlimit
.It Ic unlimit Ar resource
.It Ic unlimit Fl h
.It Ic unlimit Fl h Ar resource
Removes the limitation on
.Ar resource .
If no
.Ar resource
is specified, then all
.Ar resource
limitations are removed.
If
.Fl h
is given, the corresponding hard limits are removed.
Only the superuser may do this.
.Pp
.It Ic unset Ar pattern
All variables whose names match the specified pattern are removed.
Thus all variables are removed by
.Ic unset * ;
this has noticeably
distasteful side-effects.
It is not an error for nothing to be
.Ic unset .
.Pp
.It Ic unsetenv Ar pattern
Removes all variables whose names match the specified pattern from the
environment.
See also the
.Ic setenv
command above and
.Xr printenv 1 .
.Pp
.It Ic wait
Wait for all background jobs.
If the shell is interactive, then an interrupt can disrupt the wait.
After the interrupt, the shell prints names and job numbers of all jobs
known to be outstanding.
.Pp
.It Ic which Ar command
Displays the resolved command that will be executed by the shell.
.Pp
.It Ic while ( Ar expr )
.It \&...
.It Ic end
While the specified expression evaluates to non-zero, the commands between
the
.Ic while
and the matching
.Ic end
are evaluated.
.Ic break
and
.Ic continue
may be used to terminate or continue the loop prematurely.
(The
.Ic while
and
.Ic end
must appear alone on their input lines.)
Prompting occurs here the first time through the loop as for the
.Ic foreach
statement if the input is a terminal.
.Pp
.It Ic % Ns Ar job
Brings the specified job into the foreground.
.Pp
.It Ic % Ns Ar job Ic &
Continues the specified job in the background.
.Pp
.It Ic @
.It Ic @ Ar name Ns = expr
.It Ic @ Ar name[index] Ns = expr
The first form prints the values of all the shell variables.
The second form sets the specified
.Ar name
to the value of
.Ar expr .
If the expression contains
.Ql < ,
.Ql > ,
.Ql &
or
.Ql |
then at least
this part of the expression must be placed within
.Ql \&(
.Ql \&) .
The third form assigns the value of
.Ar expr
to the
.Ar index Ns 'th
argument of
.Ar name .
Both
.Ar name
and its
.Ar index Ns 'th
component must already exist.
.Pp
The operators
.Ql *= ,
.Ql += ,
etc. are available as in C.
The space separating the name from the assignment operator is optional.
Spaces are, however, mandatory in separating components of
.Ar expr ,
which would otherwise be single words.
.Pp
Special postfix
.Ql +\|+
and
.Ql \-\|\-
operators increment and decrement
.Ar name
respectively; i.e.,
.Dq @  i++ .
.El
.Ss Pre-defined and environment variables
The following variables have special meaning to the shell.
Of these,
.Va argv ,
.Va cwd ,
.Va home ,
.Va path ,
.Va prompt ,
.Va shell
and
.Va status
are always set by the shell.
Except for
.Ar cwd
and
.Ar status ,
this setting occurs only at initialization;
these variables will not then be modified unless done
explicitly by the user.
.Pp
The shell copies the environment variable
.Ev USER
into the variable
.Ar user ,
.Ev TERM
into
.Ar term ,
and
.Ev HOME
into
.Ar home ,
and copies these back into the environment whenever the normal
shell variables are reset.
The environment variable
.Ev PATH
is likewise handled; it is not
necessary to worry about its setting other than in the file
.Pa \&.cshrc
as inferior
.Nm
processes will import the definition of
.Ar path
from the environment, and re-export it if you then change it.
.Bl -tag -width histchars
.It Ic argv
Set to the arguments to the shell, it is from this variable that
positional parameters are substituted; i.e.,
.Dq $1
is replaced by
.Dq $argv[1] ,
etc.
.It Ic cdpath
Gives a list of alternate directories searched to find subdirectories
in
.Ic chdir
commands.
.It Ic cwd
The full pathname of the current directory.
.It Ic echo
Set when the
.Fl x
command-line option is given.
Causes each command and its arguments
to be echoed just before it is executed.
For non-built-in commands all expansions occur before echoing.
Built-in commands are echoed before command and filename substitution,
since these substitutions are then done selectively.
.It Ic filec
Enable file name completion.
.It Ic histchars
Can be given a string value to change the characters used in history
substitution.
The first character of its value is used as the
history substitution character, replacing the default character
.Ql \&! .
The second character of its value replaces the character
.Ql ^
in quick substitutions.
.It Ic histfile
Can be set to the pathname where history is going to be saved/restored.
.It Ic history
Can be given a numeric value to control the size of the history list.
Any command that has been referenced in this many events will not be
discarded.
Too large values of
.Va history
may run the shell out of memory.
The last executed command is always saved on the history list.
.It Ic home
The home directory of the invoker, initialized from the environment.
The filename expansion of
.Dq Pa ~
refers to this variable.
.It Ic ignoreeof
If set the shell ignores
end-of-file from input devices which are terminals.
This prevents shells from accidentally being killed by control-Ds.
.It Ic mail
The files where the shell checks for mail.
This checking is done after each command completion that will
result in a prompt,
if a specified interval has elapsed.
The shell says
.Dq You have new mail.
if the file exists with an access time not greater than its modify time.
.Pp
If the first word of the value of
.Ar mail
is numeric it specifies a different mail checking interval, in seconds,
than the default, which is 10 minutes.
.Pp
If multiple mail files are specified, then the shell says
.Dq New mail in Ar name
when there is mail in the file
.Ar name .
.It Ic noclobber
As described in the section on
.Sx Input/output ,
restrictions are placed on output redirection to ensure that
files are not accidentally destroyed, and that
.Ql >>
redirections
refer to existing files.
.It Ic noglob
If set, filename expansion is inhibited.
This inhibition is most useful in shell scripts that
are not dealing with filenames,
or after a list of filenames has been obtained and further expansions
are not desirable.
.It Ic nonomatch
If set, it is not an error for a filename expansion to not match any
existing files; instead the primitive pattern is returned.
It is still an error for the primitive pattern to be malformed; i.e.,
.Dq echo [
still gives an error.
.It Ic notify
If set, the shell notifies asynchronously of job completions;
the default is to present job completions just before printing
a prompt.
.It Ic path
Each word of the
.Va path
variable specifies a directory in which
commands are to be sought for execution.
A null word specifies the current directory.
If there is no
.Ar path
variable then only full path names will execute.
The usual search path is
.Dq \&. ,
.Dq /bin ,
.Dq /usr/bin ,
.Dq /sbin
and
.Dq /usr/sbin ,
but this
may vary from system to system.
For the superuser the default search path is
.Dq /bin ,
.Dq /usr/bin ,
.Dq /sbin ,
and
.Dq /usr/sbin .
A shell that is given neither the
.Fl c
nor the
.Fl t
option will normally hash the contents of the directories in the
.Ar path
variable after reading
.Ar \&.cshrc ,
and each time the
.Ar path
variable is reset.
If new commands are added to these directories
while the shell is active, it may be necessary to do a
.Ic rehash
or the commands may not be found.
.It Ic prompt
The string that is printed before each command is read from
an interactive terminal input.
If a
.Ql \&!
appears in the string it will be replaced by the current event number
unless a preceding
.Ql \e
is given.
Default is
.Dq % ,
or
.Dq #
for the superuser.
.It Ic savehist
Is given a numeric value to control the number of entries of the
history list that are saved in
.Pa ~/.history
when the user logs out.
Any command that has been referenced in this many events will be saved.
During start up the shell sources
.Pa ~/.history
into the history list
enabling history to be saved across logins.
Too large values of
.Va savehist
will slow down the shell during start up.
If
.Va savehist
is just set, the shell will use the value of
.Va history .
.It Ic shell
The file in which the shell resides.
This variable is used in forking shells to interpret files that have execute
bits set, but which are not executable by the system.
(See the description of
.Sx Non-built-in command execution
below.)
Initialized to the (system-dependent) home of the shell.
.It Ic status
The status returned by the last command.
If it terminated abnormally, then 0200 is added to the status.
Built-in commands that fail return exit status 1,
all other built-in commands set status to 0.
.It Ic time
Controls automatic timing of commands.
If set, then any command that takes more than this many
.Tn CPU
seconds
will cause a line giving user, system, and real times, and a utilization
percentage which is the ratio of user plus system times to real time
to be printed when it terminates.
.It Ic verbose
Set by the
.Fl v
command-line option, causes the words of each command to be printed
after history substitution.
.El
.Ss Non-built-in command execution
When a command to be executed is found to not be a built-in command
the shell attempts to execute the command via
.Xr execve 2 .
Each word in the variable
.Ar path
names a directory from which the shell will attempt to execute the command.
If it is given neither a
.Fl c
nor a
.Fl t
option, the shell will hash the names in these directories into an internal
table so that it will only try an
.Ic exec
in a directory if there is a possibility that the command resides there.
This shortcut greatly speeds command location when many directories
are present in the search path.
If this mechanism has been turned off (via
.Ic unhash ) ,
or if the shell was given a
.Fl c
or
.Fl t
argument, and in any case for each directory component of
.Ar path
that does not begin with a
.Ql / ,
the shell concatenates with the given command name to form a path name
of a file which it then attempts to execute.
.Pp
Parenthesized commands are always executed in a sub-shell.
Thus
.Pp
.Dl (cd ; pwd) ; pwd
.Pp
prints the
.Ar home
directory; leaving you where you were (printing this after the home directory),
while
.Pp
.Dl cd ; pwd
.Pp
leaves you in the
.Ar home
directory.
Parenthesized commands are most often used to prevent
.Ic chdir
from affecting the current shell.
.Pp
If the file has execute permissions but is not an
executable binary to the system, then it is assumed to be a
file containing shell commands and a new shell is spawned to read it.
.Pp
If there is an alias for
.Ic shell
then the words of the alias will be prepended to the argument list to form
the shell command.
The first word of the alias
should be the full path name of the shell
(e.g.,
.Dq $shell ) .
Note that this is a special, late occurring, case of
.Ic alias
substitution,
and only allows words to be prepended to the argument list without change.
.Ss Signal handling
The shell normally ignores
.Dv SIGQUIT
signals.
Jobs running detached (either by
.Ic \&&
or the
.Ic bg
or
.Ic %... &
commands) are immune to signals generated from the keyboard, including
hangups.
Other signals have the values which the shell inherited from its parent.
The shell's handling of interrupts and terminate signals
in shell scripts can be controlled by
.Ic onintr .
Login shells catch the
.Dv SIGTERM
(terminate) signal;
otherwise this signal is passed on to children from the state in the
shell's parent.
Interrupts are not allowed when a login shell is reading the file
.Pa \&.logout .
.Sh LIMITATIONS
Word lengths \-
Words can be no longer than 1024 characters.
The number of arguments to a command that involves filename expansion
is limited to 1/6th the number of characters allowed in an argument list.
Command substitutions may substitute no more characters than are
allowed in an argument list.
To detect looping, the shell restricts the number of
.Ic alias
substitutions on a single line to 20.
.Sh FILES
.Bl -tag -width /etc/passwd -compact
.It Pa ~/.cshrc
read at beginning of execution by each shell
.It Pa ~/.login
read by login shell, after
.Pa .cshrc
at login
.It Pa ~/.logout
read by login shell, at logout
.It Pa /bin/sh
standard shell, for shell scripts not starting with a
.Ql #
.It Pa /tmp/sh.*
temporary file for
.Ql <<
.It Pa /etc/passwd
source of home directories for
.Dq ~name
.El
.Sh SEE ALSO
.Xr sh 1 ,
.Xr access 2 ,
.Xr execve 2 ,
.Xr fork 2 ,
.Xr pipe 2 ,
.Xr setrlimit 2 ,
.Xr umask 2 ,
.Xr wait 2 ,
.Xr killpg 3 ,
.Xr sigvec 3 ,
.Xr tty 4 ,
.Xr a.out 5 ,
.Xr environ 7 ,
.Xr script 7
.Sh HISTORY
.Nm
appeared in
.Bx 3 .
It
was a first implementation of a command language interpreter
incorporating a history mechanism (see
.Sx History substitutions ) ,
job control facilities (see
.Sx Jobs ) ,
interactive file name
and user name completion (see
.Sx File name completion ) ,
and a C-like syntax.
There are now many shells that also have these mechanisms, plus
a few more (and maybe some bugs too), which are available through the
usenet.
.Sh AUTHORS
William Joy.
Job control and directory stack features first implemented by J.E. Kulp of
IIASA, Laxenburg, Austria,
with different syntax than that used now.
File name completion code written by Ken Greer, HP Labs.
Eight-bit implementation Christos S. Zoulas, Cornell University.
.Sh BUGS
When a command is restarted from a stop,
the shell prints the directory it started in if this is different
from the current directory; this can be misleading (i.e., wrong)
as the job may have changed directories internally.
.Pp
Shell built-in functions are not stoppable/restartable.
Command sequences of the form
.Dq a \&; b \&; c
are also not handled gracefully
when stopping is attempted.
If you suspend
.Ql b ,
the shell will immediately execute
.Ql c .
This is especially noticeable if this
expansion results from an alias.
It suffices to place the sequence of commands in ()'s to force it to
a sub-shell; i.e.,
.Dq Po a \&; b \&; c Pc .
.Pp
Control over tty output after processes are started is primitive;
perhaps this will inspire someone to work on a good virtual
terminal interface.
In a virtual terminal interface much more
interesting things could be done with output control.
.Pp
Alias substitution is most often used to clumsily simulate shell procedures;
shell procedures should be provided instead of aliases.
.Pp
Commands within loops, prompted for by
.Ql \&? ,
are not placed on the
.Ic history
list.
Control structure should be parsed instead of being recognized as built-in
commands.
This would allow control commands to be placed anywhere,
to be combined with
.Ql | ,
and to be used with
.Ql &
and
.Ql \&;
metasyntax.
.Pp
It should be possible to use the
.Ql \&:
modifiers on the output of command
substitutions.
.Pp
The way the
.Va filec
facility is implemented is ugly and expensive.