at - How to use at command in Linux

# at -h
Usage: at [-V] [-q x] [-f file] [-mMlbv] timespec ...
       at [-V] [-q x] [-f file] [-mMlbv] -t time
       at -c job ...
       atq [-V] [-q x]
       at [ -rd ] job ...
       atrm [-V] job ...
       batch

# man at

SYNOPSIS
       at -c job [job...]

DESCRIPTION
       at  and  batch  read  commands from standard input or a specified file which are to be executed at a later time,
       using /bin/sh.

       at      executes commands at a specified time.

       atq     lists the user's pending jobs, unless the user is the superuser; in  that  case,  everybody's  jobs  are
               listed.   The format of the output lines (one for each job) is: Job number, date, hour, queue, and user-
               name.

       atrm    deletes jobs, identified by their job number.

       batch   executes commands when system load levels permit; in other words, when the load average drops below 0.8,
               or the value specified in the invocation of atd.

OPTIONS
       -t time run the job at time, given in the format [[CC]YY]MMDDhhmm[.ss]
       -c      cats the jobs listed on the command line to standard output.

# echo "logger test" |at 21:00 02/30/2017 
job 2 at Thu Mar  2 21:00:00 2017
Can't open /var/run/atd.pid to signal atd. No atd running?
# atq
1       Thu Mar  2 21:00:00 2017 a root
#
# atrm 1
# atq
#

# at -t 201701091000
# logger "test"
Crtl+D
# atq
3       Mon Jan  9 10:00:00 2017 a root
# atrm 3
# atq
#

# atq   
4       Thu Mar  2 21:00:00 2017 a root
#
# at -c 4
#!/bin/sh
# atrun uid=0 gid=0
# mail infra 0
umask 22
XDG_SESSION_ID=2; export XDG_SESSION_ID
HOSTNAME=centos7; export HOSTNAME
SHELL=/bin/bash; export SHELL
HISTSIZE=1000; export HISTSIZE
USER=root; export USER
LS_COLORS=rs=0:di=01\;34:ln=01\;36:mh=00:pi=40\;33:so=01\;35:do=01\;35:bd=40\;33\;01:cd=40\;33\;01:or=40\;31\;01:mi=01\;05\;37\;41:su=37\;41:sg=30\;43:ca=30\;41:tw=30\;42:ow=34\;42:st=37\;44:ex=01\;32:\*.tar=01\;31:\*.tgz=01\;31:\*.arc=01\;31:\*.arj=01\;31:\*.taz=01\;31:\*.lha=01\;31:\*.lz4=01\;31:\*.lzh=01\;31:\*.lzma=01\;31:\*.tlz=01\;31:\*.txz=01\;31:\*.tzo=01\;31:\*.t7z=01\;31:\*.zip=01\;31:\*.z=01\;31:\*.Z=01\;31:\*.dz=01\;31:\*.gz=01\;31:\*.lrz=01\;31:\*.lz=01\;31:\*.lzo=01\;31:\*.xz=01\;31:\*.bz2=01\;31:\*.bz=01\;31:\*.tbz=01\;31:\*.tbz2=01\;31:\*.tz=01\;31:\*.deb=01\;31:\*.rpm=01\;31:\*.jar=01\;31:\*.war=01\;31:\*.ear=01\;31:\*.sar=01\;31:\*.rar=01\;31:\*.alz=01\;31:\*.ace=01\;31:\*.zoo=01\;31:\*.cpio=01\;31:\*.7z=01\;31:\*.rz=01\;31:\*.cab=01\;31:\*.jpg=01\;35:\*.jpeg=01\;35:\*.gif=01\;35:\*.bmp=01\;35:\*.pbm=01\;35:\*.pgm=01\;35:\*.ppm=01\;35:\*.tga=01\;35:\*.xbm=01\;35:\*.xpm=01\;35:\*.tif=01\;35:\*.tiff=01\;35:\*.png=01\;35:\*.svg=01\;35:\*.svgz=01\;35:\*.mng=01\;35:\*.pcx=01\;35:\*.mov=01\;35:\*.mpg=01\;35:\*.mpeg=01\;35:\*.m2v=01\;35:\*.mkv=01\;35:\*.webm=01\;35:\*.ogm=01\;35:\*.mp4=01\;35:\*.m4v=01\;35:\*.mp4v=01\;35:\*.vob=01\;35:\*.qt=01\;35:\*.nuv=01\;35:\*.wmv=01\;35:\*.asf=01\;35:\*.rm=01\;35:\*.rmvb=01\;35:\*.flc=01\;35:\*.avi=01\;35:\*.fli=01\;35:\*.flv=01\;35:\*.gl=01\;35:\*.dl=01\;35:\*.xcf=01\;35:\*.xwd=01\;35:\*.yuv=01\;35:\*.cgm=01\;35:\*.emf=01\;35:\*.axv=01\;35:\*.anx=01\;35:\*.ogv=01\;35:\*.ogx=01\;35:\*.aac=01\;36:\*.au=01\;36:\*.flac=01\;36:\*.mid=01\;36:\*.midi=01\;36:\*.mka=01\;36:\*.mp3=01\;36:\*.mpc=01\;36:\*.ogg=01\;36:\*.ra=01\;36:\*.wav=01\;36:\*.axa=01\;36:\*.oga=01\;36:\*.spx=01\;36:\*.xspf=01\;36:; export LS_COLORS
MAIL=/var/spool/mail/root; export MAIL
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin; export PATH
PWD=/root; export PWD
LANG=C; export LANG
HISTCONTROL=ignoredups; export HISTCONTROL
SHLVL=1; export SHLVL
HOME=/root; export HOME
LOGNAME=root; export LOGNAME
LESSOPEN=\|\|/usr/bin/lesspipe.sh\ %s; export LESSOPEN
cd /root || {
         echo 'Execution directory inaccessible' >&2
         exit 1
}
${SHELL:-/bin/sh} << 'marcinDELIMITER1a38f7ed'
logger test

marcinDELIMITER1a38f7ed