at (Unix)

In Unix-like computer operating systems, the at command is used to schedule commands to be executed once, at a particular time in the future.

Design

at reads a series of commands from standard input and collects them into one "at-job" which is carried out at a later date. The job inherits the current environment, so that it is executed in the same working directory and with the same environment variables set as when it was scheduled.

It differs from cron, which is used for recurring executions (e.g. once an hour, every Tuesday, January 1 every year). As with cron, many Unix systems allow the administrator to restrict access to the at command.

at can be made to mail a user when done carrying out a scheduled job of theirs, can use more than one job queue, and can read a list of jobs to carry out from a file instead of standard input.

Usage

A sample command to compile a C program at 11:45 a. m. on January 31st would be:

 $ echo "cc -o foo foo.c" | at 1145 jan 31

 $ at 1145 jan 31
 at> cc -o foo foo.c
 at> ^D #(press Control-D while at the beginning of a line)

The atq program lists the currently queued jobs, while atrm removes jobs from the queue:

$ atq
1234 2011-08-12 11:45 cc -o foo foo.c user
$ atrm 1234 
$ atq
$

In some Unix-like computer operating systems it uses a daemon, atd, which waits in the background periodically checking the list of jobs to do and executing those at their scheduled time on behalf of at.

Variants

The batch command can be used instead of at to only run scheduled jobs if the system's load average is below a certain value.

Windows NT/2000/XP/7 also has an at command (similar to cron), but it is deprecated in favor of Task Scheduler.

External links

at: execute commands at a later time – Commands & Utilities Reference, The Single UNIX® Specification, Issue 7 from The Open Group
batch: schedule commands to be executed in a batch queue – Commands & Utilities Reference, The Single UNIX® Specification, Issue 7 from The Open Group

Unix command-line interface programs and shell builtins

File system	cat chmod chown chgrp cksum cmp cp dd du df file fsck fuser ln ls mkdir mount mv pax pwd rm rmdir split tee touch type umask

Processes	at bg chroot cron fg kill killall nice pgrep pkill ps pstree time top

User environment	clear env exit finger history logname mesg passwd su sudo uptime talk tput uname w wall who whoami write

Text processing	awk banner basename comm csplit cut diff dirname ed ex fmt fold head iconv join less more nl paste printf sed sort spell strings tail tr uniq vi wc xargs yes

Shell builtins	alias cd echo test unset wait

Networking	dig host ifconfig inetd netcat netstat nslookup ping rdate rlogin route ssh traceroute

Searching	find grep locate whatis whereis

Documentation	apropos help man

Miscellaneous	bc dc cal expr lp od sleep true and false

List of Unix commands

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at (Unix)

Design

Usage

Variants

See also

External links