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
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>-X - perldoc.perl.org</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<meta http-equiv="Content-Language" content="en-gb">
<link href="../static/css-20090810.css" rel="stylesheet" rev="stylesheet" type="text/css" media="screen">
</head>
<body onLoad="perldoc.startup();" onPageShow="if (event.persisted) perldoc.startup();">
<div id="page">
<div id="header">
<div id="homepage_link">
<a href="../index.html"></a>
</div>
<div id="search_form">
<form action="../search.html" method="GET" id="search">
<input type="text" name="q" id="search_box" alt="Search">
</form>
</div>
</div>
<div id="body">
<div id="left_column">
<div class="side_group">
<div class="side_panel doc_panel">
<p>Manual</p>
<ul>
<li><a href="../index-overview.html">Overview</a>
<li><a href="../index-tutorials.html">Tutorials</a>
<li><a href="../index-faq.html">FAQs</a>
<li><a href="../index-history.html">History / Changes</a>
<li><a href="../index-licence.html">License</a>
</ul>
</div>
<div class="side_panel doc_panel">
<p>Reference</p>
<ul>
<li><a href="../index-language.html">Language</a>
<li><a href="../index-functions.html">Functions</a>
<li><a href="../perlop.html">Operators</a>
<li><a href="../perlvar.html">Special Variables</a>
<li><a href="../index-pragmas.html">Pragmas</a>
<li><a href="../index-utilities.html">Utilities</a>
<li><a href="../index-internals.html">Internals</a></li>
<li><a href="../index-platforms.html">Platform Specific</a>
</ul>
</div>
<div class="side_panel doc_panel">
<p>Modules</p>
<ul>
<li>
<a href="../index-modules-A.html">A</a>
•
<a href="../index-modules-B.html">B</a>
•
<a href="../index-modules-C.html">C</a>
•
<a href="../index-modules-D.html">D</a>
•
<a href="../index-modules-E.html">E</a>
<li>
<a href="../index-modules-F.html">F</a>
•
<a href="../index-modules-G.html">G</a>
•
<a href="../index-modules-H.html">H</a>
•
<a href="../index-modules-I.html">I</a>
•
<a href="../index-modules-L.html">L</a>
<li>
<a href="../index-modules-M.html">M</a>
•
<a href="../index-modules-N.html">N</a>
•
<a href="../index-modules-O.html">O</a>
•
<a href="../index-modules-P.html">P</a>
•
<a href="../index-modules-S.html">S</a>
<li>
<a href="../index-modules-T.html">T</a>
•
<a href="../index-modules-U.html">U</a>
•
<a href="../index-modules-X.html">X</a>
</ul>
</div>
</div>
<div class="side_group">
<div class="side_panel links_panel">
<p>News / Blogs</p>
<ul>
<li><a href="http://perlbuzz.com">Perl Buzz</a></li>
<li><a href="http://ironman.enlightenedperl.org">Perl Iron Man</a></li>
<li><a href="http://perlsphere.net">Perlsphere</a></li>
<li><a href="http://planet.perl.org">Planet Perl</a></li>
<li><a href="http://news.perlfoundation.org/">TPF news</a></li>
<li><a href="http://use.perl.org">Use Perl</a></li>
</ul>
</div>
<div class="side_panel links_panel">
<p>See also</p>
<ul>
<li><a href="http://search.cpan.org">CPAN</a></li>
<li><a href="http://www.perl.org">Perl.org</a></li>
<li><a href="http://www.perl.com">Perl.com</a></li>
<li><a href="http://www.perlfoundation.org/perl5/index.cgi">Perl 5 Wiki</a></li>
<li><a href="http://jobs.perl.org">Perl Jobs</a></li>
<li><a href="http://www.pm.org">Perl Mongers</a></li>
<li><a href="http://www.perlmonks.org">Perl Monks</a></li>
</ul>
</div>
<div class="side_panel links_panel">
<p>Contact</p>
<ul>
<li><a href="http://perl.jonallen.info">Site designed and maintained by Jon Allen (JJ)</a>
<li><a href="http://perl.jonallen.info">http://perl.jonallen.info</a>
</ul>
<ul>
<li><a href="http://perl.jonallen.info/projects/perldoc">View the project page and FAQs</a>
</ul>
</div>
</div>
</div>
<div id="centre_column">
<div id="content_header">
<div id="title_bar">
<div id="page_name">
<h1>-X</h1>
</div>
<div id="perl_version">
Perl 5 version 10.1 documentation
</div>
<div id="page_links">
<a href="#" onClick="toolbar.goToTop();return false;">Go to top</a>
</div>
</div>
<div id="breadcrumbs">
<a href="../index.html">Home</a> >
<a href="../index-language.html">Language reference</a> >
<a href="../index-functions.html">Functions</a> >
-X
</div>
</div>
<div id="content_body">
<!--[if lt IE 7]>
<div class="noscript">
<p>
<strong>It looks like you're using Internet Explorer 6. This is a very old
browser which does not offer full support for modern websites.</strong>
</p>
<p>
Unfortunately this means that this website will not work on
your computer.
</p>
<p>
Don't miss out though! To view the site (and get a better experience from
many other websites), simply upgrade to
<a href="http://www.microsoft.com/windows/Internet-explorer/default.aspx">Internet
Explorer 8</a>
or download an alternative browser such as
<a href="http://www.mozilla.com/en-US/firefox/firefox.html">Firefox</a>,
<a href="http://www.apple.com/safari/download/">Safari</a>, or
<a href="http://www.google.co.uk/chrome">Google Chrome</a>.
</p>
<p>
All of these browsers are free. If you're using a PC at work, you may
need to contact your IT administrator.
</p>
</div>
<![endif]-->
<noscript>
<div class="noscript">
<p>
<strong>Please note: Many features of this site require JavaScript. You appear to have JavaScript disabled,
or are running a non-JavaScript capable web browser.</strong>
</p>
<p>
To get the best experience, please enable JavaScript or download a modern web browser such as <a href="http://www.microsoft.com/windows/Internet-explorer/default.aspx">Internet Explorer 8</a>, <a href="http://www.mozilla.com/en-US/firefox/firefox.html">Firefox</a>, <a href="http://www.apple.com/safari/download/">Safari</a>, or <a href="http://www.google.co.uk/chrome">Google Chrome</a>.
</p>
</div>
</noscript>
<div id="from_search"></div>
<h1>-X</h1>
<div class="mod_az_list">
<a href="../index-functions.html">Perl functions A-Z</a> |
<a href="../index-functions-by-cat.html">Perl functions by category</a> |
<a href="../perlfunc.html">The 'perlfunc' manpage</a>
</div>
<!-- -->
<ul>
<li><a name="-X-FILEHANDLE"></a><b>-X FILEHANDLE</b>
<p>
</p>
</li>
</ul>
<ul>
<li><a name="-X-EXPR"></a><b>-X EXPR</b>
</li>
<li><a name="-X-DIRHANDLE"></a><b>-X DIRHANDLE</b>
</li>
<li><a name="-X"></a><b>-X</b>
<p>A file test, where X is one of the letters listed below. This unary
operator takes one argument, either a filename, a filehandle, or a dirhandle,
and tests the associated file to see if something is true about it. If the
argument is omitted, tests <code class="inline"><span class="i">$_</span></code>
, except for <code class="inline">-t</code>
, which tests STDIN.
Unless otherwise documented, it returns <code class="inline"><span class="n">1</span></code>
for true and <code class="inline"><span class="q">''</span></code>
for false, or
the undefined value if the file doesn't exist. Despite the funny
names, precedence is the same as any other named unary operator. The
operator may be any of:</p>
<pre class="verbatim"><ol><li> -r File is readable by effective uid/gid.</li><li> -w File is writable by effective uid/gid.</li><li> -x File is executable by effective uid/gid.</li><li> -o File is owned by effective uid.</li><li></li><li> -R File is readable by real uid/gid.</li><li> -W File is writable by real uid/gid.</li><li> -X File is executable by real uid/gid.</li><li> -O File is owned by real uid.</li><li></li><li> -e File exists.</li><li> -z File has zero size (is empty).</li><li> -s File has nonzero size (returns size in bytes).</li><li></li><li> -f File is a plain file.</li><li> -d File is a directory.</li><li> -l File is a symbolic link.</li><li> -p File is a named pipe (FIFO), or Filehandle is a pipe.</li><li> -S File is a socket.</li><li> -b File is a block special file.</li><li> -c File is a character special file.</li><li> -t Filehandle is opened to a tty.</li><li></li><li> -u File has setuid bit set.</li><li> -g File has setgid bit set.</li><li> -k File has sticky bit set.</li><li></li><li> -T File is an ASCII text file (heuristic guess).</li><li> -B File is a "binary" file (opposite of -T).</li><li></li><li> -M Script start time minus file modification time, in days.</li><li> -A Same for access time.</li><li> -C Same for inode change time (Unix, may differ for other platforms)</li></ol></pre><p>Example:</p>
<pre class="verbatim"><ol><li> while <span class="s">(</span><><span class="s">)</span> <span class="s">{</span></li><li> <a class="l_k" href="../functions/chomp.html">chomp</a><span class="sc">;</span></li><li> <a class="l_k" href="../functions/next.html">next</a> unless -f <span class="i">$_</span><span class="sc">;</span> <span class="c"># ignore specials</span></li><li> <span class="c">#...</span></li><li> <span class="s">}</span></li></ol></pre><p>The interpretation of the file permission operators <code class="inline">-r</code>
, <code class="inline">-R</code>
,
<code class="inline">-w</code>
, <code class="inline">-W</code>
, <code class="inline">-x</code>
, and <code class="inline"><a class="l_k" href="../functions/-X.html">-X</a></code> is by default based solely on the mode
of the file and the uids and gids of the user. There may be other
reasons you can't actually read, write, or execute the file: for
example network filesystem access controls, ACLs (access control lists),
read-only filesystems, and unrecognized executable formats. Note
that the use of these six specific operators to verify if some operation
is possible is usually a mistake, because it may be open to race
conditions.</p>
<p>Also note that, for the superuser on the local filesystems, the <code class="inline">-r</code>
,
<code class="inline">-R</code>
, <code class="inline">-w</code>
, and <code class="inline">-W</code>
tests always return 1, and <code class="inline">-x</code>
and <code class="inline"><a class="l_k" href="../functions/-X.html">-X</a></code> return 1
if any execute bit is set in the mode. Scripts run by the superuser
may thus need to do a stat() to determine the actual mode of the file,
or temporarily set their effective uid to something else.</p>
<p>If you are using ACLs, there is a pragma called <code class="inline"><span class="w">filetest</span></code>
that may
produce more accurate results than the bare stat() mode bits.
When under the <code class="inline"><a class="l_k" href="../functions/use.html">use</a> <span class="w">filetest</span> <span class="q">'access'</span></code>
the above-mentioned filetests
will test whether the permission can (not) be granted using the
access() family of system calls. Also note that the <code class="inline">-x</code>
and <code class="inline"><a class="l_k" href="../functions/-X.html">-X</a></code> may
under this pragma return true even if there are no execute permission
bits set (nor any extra execute permission ACLs). This strangeness is
due to the underlying system calls' definitions. Note also that, due to
the implementation of <code class="inline"><a class="l_k" href="../functions/use.html">use</a> <span class="w">filetest</span> <span class="q">'access'</span></code>
, the <code class="inline"><span class="w">_</span></code>
special
filehandle won't cache the results of the file tests when this pragma is
in effect. Read the documentation for the <code class="inline"><span class="w">filetest</span></code>
pragma for more
information.</p>
<p>Note that <code class="inline">-s/a/b/</code> does not do a negated substitution. Saying
<code class="inline">-<a class="l_k" href="../functions/exp.html">exp</a><span class="s">(</span><span class="i">$foo</span><span class="s">)</span></code>
still works as expected, however--only single letters
following a minus are interpreted as file tests.</p>
<p>The <code class="inline">-T</code>
and <code class="inline">-B</code>
switches work as follows. The first block or so of the
file is examined for odd characters such as strange control codes or
characters with the high bit set. If too many strange characters (>30%)
are found, it's a <code class="inline">-B</code>
file; otherwise it's a <code class="inline">-T</code>
file. Also, any file
containing null in the first block is considered a binary file. If <code class="inline">-T</code>
or <code class="inline">-B</code>
is used on a filehandle, the current IO buffer is examined
rather than the first block. Both <code class="inline">-T</code>
and <code class="inline">-B</code>
return true on a null
file, or a file at EOF when testing a filehandle. Because you have to
read a file to do the <code class="inline">-T</code>
test, on most occasions you want to use a <code class="inline">-f</code>
against the file first, as in <code class="inline"><a class="l_k" href="../functions/next.html">next</a> unless -f <span class="i">$file</span> && -T <span class="i">$file</span></code>
.</p>
<p>If any of the file tests (or either the <code class="inline"><a class="l_k" href="../functions/stat.html">stat</a></code> or <code class="inline"><a class="l_k" href="../functions/lstat.html">lstat</a></code> operators) are given
the special filehandle consisting of a solitary underline, then the stat
structure of the previous file test (or stat operator) is used, saving
a system call. (This doesn't work with <code class="inline">-t</code>
, and you need to remember
that lstat() and <code class="inline">-l</code>
will leave values in the stat structure for the
symbolic link, not the real file.) (Also, if the stat buffer was filled by
an <code class="inline"><a class="l_k" href="../functions/lstat.html">lstat</a></code> call, <code class="inline">-T</code>
and <code class="inline">-B</code>
will reset it with the results of <code class="inline"><a class="l_k" href="../functions/stat.html">stat</a> <span class="w">_</span></code>
).
Example:</p>
<pre class="verbatim"><ol><li> <a class="l_k" href="../functions/print.html">print</a> <span class="q">"Can do.\n"</span> if -r <span class="i">$a</span> || -w <span class="i">_</span> || -x <span class="i">_</span><span class="sc">;</span></li><li></li><li> <a class="l_k" href="../functions/stat.html">stat</a><span class="s">(</span><span class="i">$filename</span><span class="s">)</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/print.html">print</a> <span class="q">"Readable\n"</span> if -r <span class="i">_</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/print.html">print</a> <span class="q">"Writable\n"</span> if -w <span class="i">_</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/print.html">print</a> <span class="q">"Executable\n"</span> if -x <span class="i">_</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/print.html">print</a> <span class="q">"Setuid\n"</span> if -u <span class="i">_</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/print.html">print</a> <span class="q">"Setgid\n"</span> if -g <span class="i">_</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/print.html">print</a> <span class="q">"Sticky\n"</span> if -k <span class="i">_</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/print.html">print</a> <span class="q">"Text\n"</span> if -T <span class="i">_</span><span class="sc">;</span></li><li> <a class="l_k" href="../functions/print.html">print</a> <span class="q">"Binary\n"</span> if -B <span class="i">_</span><span class="sc">;</span></li></ol></pre><p>As of Perl 5.9.1, as a form of purely syntactic sugar, you can stack file
test operators, in a way that <code class="inline">-f -w -x <span class="i">$file</span></code>
is equivalent to
<code class="inline">-x <span class="i">$file</span> && -w <span class="i">_</span> && -f <span class="i">_</span></code>
. (This is only syntax fancy: if you use
the return value of <code class="inline">-f <span class="i">$file</span></code>
as an argument to another filetest
operator, no special magic will happen.)</p>
</li>
</ul>
</div>
<div id="content_footer">
</div>
</div>
<div id="right_column">
<div class="side_group">
<div class="side_panel tools_panel">
<p>Recently read</p>
<div id="recent_pages"></div>
</div>
<div class="side_panel tools_panel">
<p>Tools</p>
<ul>
<li><a href="../preferences.html">Preferences</a>
</ul>
</div>
</div>
</div>
<div class="clear"></div>
</div>
<div id="footer">
<div id="footer_content">
</div>
</div>
</div>
<script language="JavaScript" src="../static/combined-20090809.js" type="text/javascript"></script>
<script language="JavaScript" type="text/javascript">
perldoc.setPath(1);
perldoc.pageName = '-X';
perldoc.pageAddress = 'functions/-X.html';
perldoc.contentPage = 1;
</script>
</body>
</html>
|
