How to insert a line into a crontab AFTER a key word or string via script

Question

I understand there is a lot of documentation on editing crontabs via script, and I can do this by adding an entry with the following command:

line="* * * * * /my/folder/script.sh"
( crontab -l ; echo "$line" ) | crontab -

However, myself and a few others each have our own "sections" in our crontab under a superuser.

How can I insert this line under a keyword or string, such as underneath the line containing SPECIAL_JOB so as not to disturb others' sections and entries? I don't want to just keep appending new jobs at the bottom of the crontab.

The cron entry would look like this:

# SPECIAL_JOB
* * * * * /my/folder/script.sh

Ideally, I would delete the previous entry at this line to keep a single, fresh entry using this:

#remove entry
crontab -l | grep -ve '/my/folder/script.sh' | crontab -

Answer 1

This inserts after all # SPECIAL_JOB lines the $line string.

crontab -l | sed '/# SPECIAL_JOB/a'"$line" | crontab -

Answer 2

To avoid any issues with special characters in the replacement text, I would put the new cron entry into a file, named for example new-entry, then use:

{ crontab -l | sed '/^# SPECIAL_JOB/{
n
r /path/to/new-entry
d
}' } | crontab -

I made a minor change of subshell parenthesis ( ... ) to simple curly braces { ... }, because there's no real need to create a subshell; no harm, either!

I then use sed to parse the incoming text; it looks for a line that starts with # SPECIAL_JOB and then performs three actions:

1. prints the current line then reads in the next line (this lets # SPECIAL_JOB be printed)
2. r reads in the job from your file
3. d then deletes the line that used to follow # SPECIAL_JOB -- the old job.

Answer 3

I would suggest using ansible un a larger scale.