Fixed the phrasing of the manual page, tanks to Reuben Thomas, and
included 積丹尼 Dan Jacobson's nice example into crontab.5
Index: cron/crontab.5
===================================================================
--- cron.orig/crontab.5
+++ cron/crontab.5
@@ -16,8 +16,8 @@
 .\" */
 .\"
 .\" $Id: crontab.5,v 2.4 1994/01/15 20:43:43 vixie Exp $
-.\"
-.TH CRONTAB 5 "19 April 2010"
+.\" 
+.TH CRONTAB 5 "24 January 1994"
 .UC 4
 .SH NAME
 crontab \- tables for driving cron
@@ -34,19 +34,15 @@ their own crontabs, eliminating the need
 as part of a cron command.
 .PP
 Blank lines and leading spaces and tabs are ignored.  Lines whose first
-non-space character is a hash-sign (#) are comments, and are ignored.
+non-space character is a pound-sign (#) are comments, and are ignored.
 Note that comments are not allowed on the same line as cron commands, since
 they will be taken to be part of the command.  Similarly, comments are not
 allowed on the same line as environment variable settings.
 .PP
 An active line in a crontab will be either an environment setting or a cron
-command.  The crontab file is parsed from top to bottom, so any environment
-settings will affect only the cron commands below them in the file.
-An environment setting is of the form,
-.PP
-.in +4n
-name = value
-.in
+command.  An environment setting is of the form,
+.PP
+    name = value
 .PP
 where the spaces around the equal-sign (=) are optional, and any subsequent
 non-leading spaces in
@@ -56,99 +52,33 @@ will be part of the value assigned to
 The
 .I value
 string may be placed in quotes (single or double, but matching) to preserve
-leading or trailing blanks.  To define an empty variable, quotes
-.B must
-be used.
-.PP
-The
-.I value
-string is
-.B not
-parsed for environmental substitutions or replacement of variables or
-tilde(~) expansion, thus lines like
+leading or trailing blanks.
 .PP
-.in +4n
-.nf
-PATH = $HOME/bin:$PATH
-PATH = ~/bin:/usr/bin:/bin
-.fi
-.in
-.PP
-will not work as you might expect. And neither will this work
-.PP
-.in +4n
-.nf
-A=1
-B=2
-C=$A $B
-.fi
-.in
-.PP
-There will not be any substitution for the defined variables in the
-last value.
-.PP
-Several environment variables are set up automatically by the
+Several environment variables are set up
+automatically by the
 .IR cron (8)
 daemon.
-SHELL is set to /bin/sh, and LOGNAME and HOME are set from the /etc/passwd
-line of the crontab's owner.  PATH is set to "/usr/bin:/bin".
-HOME, SHELL, and PATH may be overridden by settings in the crontab;
-LOGNAME is the user that the job is running from, and may not be changed.
+SHELL is set to /bin/sh, and LOGNAME and HOME are set from the /etc/passwd 
+line of the crontab's owner.
+HOME and SHELL may be overridden by settings in the crontab; LOGNAME may not.
 .PP
 (Another note: the LOGNAME variable is sometimes called USER on BSD systems...
 on these systems, USER will be set also.)
 .PP
 In addition to LOGNAME, HOME, and SHELL,
 .IR cron (8)
-will look at MAILTO and MAILFROM if it has any reason to send mail as a result
-of running commands in ``this'' crontab.
-.PP
-If MAILTO is defined (and non-empty), mail is sent to the user so named.
-MAILTO may also be used to direct mail to multiple recipients by separating
-recipient users with a comma.  If MAILTO is defined but empty (MAILTO=""),
-no mail will be sent.  Otherwise mail is sent to the owner of the crontab.
-.PP
-If MAILFROM is defined, the sender email address is set to MAILFROM. Otherwise
-mail is sent as "root (Cron Daemon)".
-.PP
-On the Debian GNU/Linux system, cron supports the
-.B pam_env
-module, and loads the environment specified by
-.I /etc/environment
-and
-.IR /etc/security/pam_env.conf .
-It also reads locale information from
-.IR /etc/default/locale .
-However, the PAM settings do
-.B NOT
-override the settings described above nor any settings in the
-.I crontab
-file itself.  Note in particular that if you want a PATH other than
-"/usr/bin:/bin", you will need to set it in the crontab file.
-.PP
-By default, cron will send mail using the mail "Content-Type:" header of
-"text/plain" with the "charset=" parameter set to the charmap / codeset of the
-locale in which
-.IR crond (8)
-is started up \(en i.e.\& either the default system locale,
-if no LC_* environment variables are set, or the locale specified by
-the LC_* environment variables
-( see
-.IR locale (7) ).
-You can use different character encodings for mailed cron job output by
-setting the CONTENT_TYPE and CONTENT_TRANSFER_ENCODING variables in crontabs,
-to the correct values of the mail headers of those names.
+will look at MAILTO if it has any reason to send mail as a result of running
+commands in ``this'' crontab.  If MAILTO is defined (and non-empty), mail is
+sent to the user so named.  If MAILTO is defined but empty (MAILTO=""), no
+mail will be sent.  Otherwise mail is sent to the owner of the crontab.  This
+option is useful if you decide on /bin/mail instead of /usr/lib/sendmail as
+your mailer when you install cron -- /bin/mail doesn't do aliasing, and UUCP
+usually doesn't read its mail.
 .PP
 The format of a cron command is very much the V7 standard, with a number of
 upward-compatible extensions.  Each line has five time and date fields,
-followed by a command, followed by a newline character ('\en').
-The system crontab (/etc/crontab) uses the same format, except that
-the username for the command is specified after the time and
-date fields and before the command.  The fields may be separated
-by spaces or tabs.  The maximum permitted length for the command field is
-998 characters.
-.PP
-Commands are executed by
+followed by a user name if this is the system crontab file,
+followed by a command.  Commands are executed by
 .IR cron (8)
 when the minute, hour, and month of year fields match the current time,
 .I and
@@ -163,30 +93,30 @@ field	allowed values
 .br
 -----	--------------
 .br
-minute	0\(en59
+minute	0-59
 .br
-hour	0\(en23
+hour	0-23
 .br
-day of month	1\(en31
+day of month	0-31
 .br
-month	1\(en12 (or names, see below)
+month	0-12 (or names, see below)
 .br
-day of week	0\(en7 (0 or 7 is Sun, or use names)
+day of week	0-7 (0 or 7 is Sun, or use names)
 .br
 .PP
 A field may be an asterisk (*), which always stands for ``first\-last''.
 .PP
 Ranges of numbers are allowed.  Ranges are two numbers separated
 with a hyphen.  The specified range is inclusive.  For example,
-8\-11 for an ``hours'' entry specifies execution at hours 8, 9, 10
+8-11 for an ``hours'' entry specifies execution at hours 8, 9, 10
 and 11.
 .PP
 Lists are allowed.  A list is a set of numbers (or ranges)
-separated by commas.  Examples: ``1,2,5,9'', ``0\-4,8\-12''.
+separated by commas.  Examples: ``1,2,5,9'', ``0-4,8-12''.
 .PP
 Step values can be used in conjunction with ranges.  Following
 a range with ``/<number>'' specifies skips of the number's value
-through the range.  For example, ``0\-23/2'' can be used in the hours
+through the range.  For example, ``0-23/2'' can be used in the hours
 field to specify command execution every other hour (the alternative
 in the V7 standard is ``0,2,4,6,8,10,12,14,16,18,20,22'').  Steps are
 also permitted after an asterisk, so if you want to say ``every two
@@ -201,220 +131,60 @@ The ``sixth'' field (the rest of the lin
 run.
 The entire command portion of the line, up to a newline or %
 character, will be executed by /bin/sh or by the shell
-specified in the SHELL variable of the crontab file.
+specified in the SHELL variable of the cronfile.
 Percent-signs (%) in the command, unless escaped with backslash
-(\e), will be changed into newline characters, and all data
+(\\), will be changed into newline characters, and all data
 after the first % will be sent to the command as standard
-input.  There is no way to split a single command line onto multiple
-lines, like the shell's trailing "\e".
+input.
 .PP
 Note: The day of a command's execution can be specified by two
 fields \(em day of month, and day of week.  If both fields are
-restricted (i.e., don't start with *), the command will be run when
+restricted (ie, aren't *), the command will be run when
 .I either
 field matches the current time.  For example,
 .br
 ``30 4 1,15 * 5''
 would cause a command to be run at 4:30 am on the 1st and 15th of each
-month, plus every Friday.  One can, however, achieve the desired result
-by adding a test to the command (see the last example in EXAMPLE CRON FILE
-below).
-.PP
-Instead of the first five fields, one of eight special strings may appear:
-.IP
-.ta 1.5i
-string	meaning
-.br
-------	-------
-.br
-@reboot	Run once, at startup.
-.br
-@yearly	Run once a year, "0 0 1 1 *".
-.br
-@annually	(same as @yearly)
-.br
-@monthly	Run once a month, "0 0 1 * *".
-.br
-@weekly	Run once a week, "0 0 * * 0".
-.br
-@daily	Run once a day, "0 0 * * *".
-.br
-@midnight	(same as @daily)
-.br
-@hourly	Run once an hour, "0 * * * *".
-.br
-.PP
-Please note that startup, as far as @reboot is concerned, is the time when
-the
-.IR cron (8)
-daemon startup.  In particular, it may be before some system daemons,
-or other facilities, were startup.  This is due to the boot order
-sequence of the machine.
-
+month, plus every Friday.
 .SH EXAMPLE CRON FILE
-
-The following lists an example of a user crontab file.
-
 .nf
 
-# use /bin/bash to run commands, instead of the default /bin/sh
-SHELL=/bin/bash
+# use /bin/sh to run commands, no matter what /etc/passwd says
+SHELL=/bin/sh
 # mail any output to `paul', no matter whose crontab this is
 MAILTO=paul
 #
 # run five minutes after midnight, every day
 5 0 * * *       $HOME/bin/daily.job >> $HOME/tmp/out 2>&1
-# run at 2:15pm on the first of every month \(em output mailed to paul
+# run at 2:15pm on the first of every month -- output mailed to paul
 15 14 1 * *     $HOME/bin/monthly
 # run at 10 pm on weekdays, annoy Joe
-0 22 * * 1\-5    mail \-s "It's 10pm" joe%Joe,%%Where are your kids?%
-23 0\-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"
-5 4 * * sun     echo "run at 5 after 4 every Sunday"
-0 */4 1 * mon   echo "run every 4th hour on the 1st and on every Monday"
-0 0 */2 * sun   echo "run at midn on every Sunday that's an uneven date"
-# Run on every second Saturday of the month
-0 4 8\-14 * *    test $(date +\e%u) \-eq 6 && echo "2nd Saturday"
+0 22 * * 1-5	mail -s "It's 10pm" joe%Joe,%%Where are your kids?%
+23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"
+5 4 * * sun     echo "run at 5 after 4 every sunday"
+# Run once every 9th day, even across week, month, and year boundaries:
+33 22 * * *     expr $(date +\%s) / 60 / 60 / 24 \% 9 > /dev/null || echo Wax the floor.
 .fi
-
-.PP
-All the above examples run non-interactive programs.  If you wish to run a
-program that interacts with the user's desktop you have to make sure the proper
-environment variable
-.I DISPLAY
-is set.
-
-.\" Note: Based on some web searches, below example might not fully
-.\" work in all systems, as notify-send might require also
-.\" to have knowledge of the dbus session in use (through the environment)
-.\" However, adding that code here is an overkill
-.nf
-# Execute a program and run a notification every day at 10:00 am
-0 10 * * *  $HOME/bin/program | DISPLAY=:0 notify-send "Program run" "$(cat)"
-.fi
-
-.SH EXAMPLE SYSTEM CRON FILE
-
-The following lists the content of a regular system-wide crontab file.  Unlike a
-user's crontab, this file has the username field, as used by /etc/crontab.
-
-.nf
-# /etc/crontab: system-wide crontab
-# Unlike any other crontab you don't have to run the `crontab'
-# command to install the new version when you edit this file
-# and files in /etc/cron.d.  These files also have username fields,
-# that none of the other crontabs do.
-
-SHELL=/bin/sh
-PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
-
-# Example of job definition:
-# .---------------- minute (0 - 59)
-# |  .------------- hour (0 - 23)
-# |  |  .---------- day of month (1 - 31)
-# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
-# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
-# |  |  |  |  |
-# m h dom mon dow user	command
-17 * * * *  root  cd / && run-parts \-\-report /etc/cron.hourly
-25 6 * * *  root  test \-x /usr/sbin/anacron || ( cd / && run-parts \-\-report /etc/cron.daily )
-47 6 * * 7  root  test \-x /usr/sbin/anacron || ( cd / && run-parts \-\-report /etc/cron.weekly )
-52 6 1 * *  root  test \-x /usr/sbin/anacron || ( cd / && run-parts \-\-report /etc/cron.monthly )
-#
-.fi
-
-Note that all the system-wide tasks will run, by default, from 6 am to 7 am.  In
-the case of systems that are not powered on during that period of time, only
-the hourly tasks will be executed unless the defaults above are changed.
-
-
 .SH SEE ALSO
 cron(8), crontab(1)
 .SH EXTENSIONS
 When specifying day of week, both day 0 and day 7 will be considered Sunday.
-BSD and AT&T seem to disagree about this.
+BSD and ATT seem to disagree about this.
 .PP
-Lists and ranges are allowed to co-exist in the same field.
-"1\-3,7\-9" would be rejected by AT&T or BSD cron \(em they want
-to see "1\-3" or "7,8,9" ONLY.
+Lists and ranges are allowed to co-exist in the same field.  "1-3,7-9" would
+be rejected by ATT or BSD cron -- they want to see "1-3" or "7,8,9" ONLY.
 .PP
-Ranges can include "steps", so "1\-9/2" is the same as "1,3,5,7,9".
+Ranges can include "steps", so "1-9/2" is the same as "1,3,5,7,9".
 .PP
-Months or days of the week can be specified by name.
+Names of months or days of the week can be specified by name.
 .PP
-Environment variables can be set in the crontab.  In BSD or AT&T, the
+Environment variables can be set in the crontab.  In BSD or ATT, the
 environment handed to child processes is basically the one from /etc/rc.
 .PP
 Command output is mailed to the crontab owner (BSD can't do this), can be
 mailed to a person other than the crontab owner (SysV can't do this), or the
 feature can be turned off and no mail will be sent at all (SysV can't do this
 either).
-.PP
-All of the `@' commands that can appear in place of the first five fields
-are extensions.
-.SH LIMITATIONS
-The
-.I cron
-daemon runs with a defined timezone.  It currently does not support
-per-user timezones.  All the tasks: system's and user's will be run based on the
-configured timezone.  Even if a user specifies the
-.I TZ
-environment variable in his
-.I crontab
-this will affect only the commands executed in the crontab, not the execution
-of the crontab tasks themselves. If one wants to specify a particular
-timezone for crontab tasks, one may check the date in the child script,
-for example:
-
-.nf
-    # m h  dom mon dow   command
-
-    SHELL=/bin/bash
-    TZ=Australia/Sydney
-    0 * * * * [ "$(date +\\%H\\%M)" == "0000" ] && run_some_script
-.fi
-
-POSIX specifies that the day of month and the day of week fields both need to
-match the current time if either of them
-.I is
-a *.  However, this implementation only checks if the
-.I first character
-is a *.  This is why "0 0 */2 * sun" runs every Sunday that's an
-uneven date while the POSIX standard would have it run every Sunday and on
-every uneven date.
-
-The
-.I crontab
-syntax does not make it possible to define all possible periods one can
-imagine.  For example, it is not straightforward to define the last
-weekday of a month.
-To have a task run in a time period that cannot be defined using
-.I crontab
-syntax, the best approach would be to have the program itself check the
-date and time information and continue execution only if the period
-matches the desired one.
-
-If the program itself cannot do the checks then a wrapper script would be
-required.  Useful tools that could be used for date analysis are
-.I ncal
-or
-.I calendar
-For example, to run a program the last Saturday of every month you could use
-the following wrapper code:
-
-.nf
-0 4 * * Sat   [ "$(date +\e%e)" = "$(LANG=C ncal | sed \-n 's/^Sa .* \e([0\-9]\e+\e) *$/\e1/p')" ] && echo "Last Saturday" && program_to_run
-.fi
-
-
-.SH DIAGNOSTICS
-cron requires that each entry in a crontab end in a newline character.  If the
-last entry in a crontab is missing a newline (i.e.\& terminated by EOF),
-cron will consider the crontab (at least partially) broken.
-A warning will be written to syslog.
-
 .SH AUTHOR
-Paul Vixie <paul@vix.com> is the author of
-.I cron
-and original creator of this manual page.  This page has also been modified for
-Debian by Steve Greenland, Javier Fernandez-Sanguino, Christian Kastner and
-Christian Pekeler.
+.nf
+Paul Vixie <paul@vix.com>