.\" Copyright (c) 1980, 1990 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" %sccs.include.redist.man%
.\"
.\"     @(#)at.1	6.3 (Berkeley) 06/11/90
.\"
.Dd 
.Dt AT 1
.Dd 
.Os BSD 4
.Sh NAME
.Nm at
.Sd run command(s) at a specific time
.Sh SYNOPSIS
.Nm at
.Op Fl c
.Op Fl s
.Op Fl m
.Ar time
.Op Ar day
.Op Ar command_file
.Sh DESCRIPTION
.Nm At
allows commands to be run at a user specified time.
The commands can be given to
.Nm
via the
.Ar command_file
or accepted from the standard input.
.Nm At
will pass these commands to the appropriate
shell at the requested time.
.Tp Fl c
.Ar Command_file
contains
.Xr csh 1
commands.
.Tp Fl s
.Ar Command_file
contains
.Xr sh 1
commands.
.Tp Fl m
Mail will be sent to the user after the job
has been run. If errors occur during execution of the job, then
a copy of the error diagnostics will be sent to the user. If
no errors occur, then a short message is sent informing the
user that no errors occurred.
.Tp
.Pp
If no file name is specified,
.Nm at
prompts for commands from standard input until a
.Li \&^D is typed.
.Pp
The format of the spool file is as follows:
A four line header that includes the owner of the job, the name of the job,
the shell used to run the job, and whether mail will be
set after the job is executed. The header is followed by a
.Ic cd
command to the current directory and a
.Ic umask
command to set the modes on any files created by the job.
Then
.Nm at
copies all relevant environment variables to the spool file.
When the script is run, it uses the user and group ID
of the creator of the spool file.
.Pp
The
.Ar time
is either a 24 hour military time
.Em hhmm,
where
.Em hh
is hour and
.Em mm
is minutes, or the traditional 12 hour time
with qualifying options:
.Df I
.Dp Li am
am
.Dp Li a
am
.Dp Li pm
pm
.Dp Li p
pm
.Dp Li n
noon
.Dp Li m
midnight
.Dp
.De
The time can be abbreviated as shown below in the EXAMPLES.
.Pp
A
.Ar day
of the week may be specified by the first two
letters of its name. A week (7 days) may be specified by 
the argument
.Em week .
If a month name is given, the following argument is expected to
be the day.
.Sh ENVIRONMENT
If no shell is specified,
the current environment variable
.Ev SHELL
is used.
Examples
.Pp
.Dp Li at 10p
Execute at 10pm today, or tomorrow
if 10pm has past. Use the shell
found in the environment variable
.Ev SHELL.
.Dp Li at -c -m 1705 mo
Execute at 5:05pm on Monday using
.Xr csh 1
and send mail upon completion or
termination of the job.
.Dp Li at -s -m 1200n week
Use
.Xr sh 1 ,
send mail upon completetion, start at noon o'clock,
one week from today.
.Dp Li at -s 8a apr 1
Try it for fun.
.Dp
.Pp
.Sh ERRORS
Errors must be collected via the
.Fl m
option or by redirecting the standard output
from inside the
.Ar command_file.
.Sh FILES
.Dw /var/spool/at/yy.ddd.hhhh.*
.Ds L
.Dp Pa /var/spool/at
spooling area
.Dp Pa /var/spool/at/yy.ddd.hhhh.*
job file
.Dp Pa /var/spool/at/past
directory where jobs are executed from
.Dp Pa /var/spool/at/lasttimedone
last time atrun was run
.Dp Pa /var/libexec/atrun
executor (run by
.Xr cron 8 )
.Dp
.Sh SEE ALSO
.Xr atq 1 ,
.Xr atrm 1 ,
.Xr calendar 1 ,
.Xr cron 8
.Xr sleep 1 ,
.Sh DIAGNOSTICS
Complains about various syntax errors and times out of range.
.Sh HISTORY
.Nm
appeared in Version 7 AT&T UNIX.
.Sh BUGS
The queueing mechanism
.Pa /usr/libexec/atrun ,
is scheduled by
.Xr cron 8 .
Frequency with which
.Xr cron 8
runs
.Pa /usr/libexec/atrun
is site dependent.
If it is run infrequently, a job may
fall thru the cracks.
.Pp
There are known problems attempting to specify
a time of 2400 hours to
.Nm at .
.Pp
If the system crashes, mail is not sent to the user informing them that
the job was not completed.
.Pp
Sometimes old spool files are not removed from the directory
/var/spool/at/past. This is usually due to a system crash,
and requires that they be removed by hand.