About the author

My name is Solène Rapenne. I like learning and sharing experiences about IT stuff. Hobbies: '(BSD OpenBSD h+ Lisp cmdline gaming internet-stuff Crossbow). I love % and lambda characters. OpenBSD developer solene@.

Contact : solene on Freenode or solene+www at dataswamp dot org

Deploying cron programmaticaly the unix way

Written by Solène, on 31 May 2018.
Tags: #unix

Here is a little script to automatize in some way your crontab deployment when you don’t want to use a configuration tool like ansible/salt/puppet etc…

The script works this way:

./install_cron crontab_solene

with crontab_solene file being an actual crontab correct, which could looks like this:

## TAG ##
MAILTO=""
*/5 * * * *  ( cd ~/dev/reed-alert && ecl --load check.lisp )
*/10 * * * * /usr/local/bin/r2e run
1 * * * * vacuumdb -azf -U postgres
## END_TAG ##

Then it will include the file into my current user crontab, the TAG in the file is here to be able to remove it and replace it later with the new version. The script could be easily modified to support the tag name as parameter, if you have multiple deploymenets using the same user on the same machine.

#!/bin/sh

if [ -z "$1" ]; then
    echo "Usage: $0 user_crontab_file"
    exit 1
fi

VALIDATION=0
grep "^## TAG ##$" "$1" >/dev/null
VALIDATION=$?
grep "^## END_TAG ##$" "$1" >/dev/null
VALIDATION=$(( VALIDATION + $? ))

if [ "$VALIDATION" -ne 0 ]
then
    echo "file ./${1} needs \"## TAG ##\" and \"## END_TAG ##\" to be used"
    exit 2
fi

crontab -l | \
    awk '{ if($0=="## TAG ##") { hide=1 };  if(hide==0) { print } ; if($0=="## END_TAG ##") { hide=0 }; }' | \
    cat - "${1}" | \
    crontab -