Re: How to use sed to remove a line from a cron file and also remove all commented lines directly above it

On 09Jul2012 21:30, [email protected] <[email protected]> wrote:
| I realize you can't just run sed on a cron file, but I need to run sed to 

If you're root you probably can, though you'd need to restart cron to
make it see the changes.

| delete the command and all commented lines directly above the removed line. 
| 
| Basically, for any text file like below, remove the line containing the pattern 
| 
| and any commented lines directly above it. 
| 
| In the text below, I want to remove every line from the line beginning with Purge 
| 
| through the line containing the pattern $BACKUPDIR/runBackup.sh . 
| 
| Any ideas? 

Do it in two steps. First, write the sed script and test it against a
copy of the crontab. Make the sed script a standalone file in its own
right i.e. not just "sed -e 'blah'" on the command line but "sed -f
sed_script.txt". Personally, I would be commenting out the lines
instead of removing them because my paranoia is great. Eg, put:

  ## autoremoved - YYYYMMDD ## 

on the front of the lines. Next time someone hand edits the file they
can go for real with a human's eye on them.

Second, invoke the "crontab -e" command with editor set to

  sed -i -f sed_script.txt

i.e.

  EDITOR='sed -i -f sed_script.txt' crontab -e -u username

Regarding the script itself, I suppose something like this (totally
untested):

  /^# Purge/,/^[^#].*runAnotherCmd.sh/s/^/## autoremoved - YYYYMMDD ##/

Obviously, adjust to suit. (And "d" instead of "s///" if you're you and
not me.)

If your system's sed does not have the -i option you can used "bsed" instead
of "sed -i":

  https://bitbucket.org/cameron_simpson/css/src/tip/bin/bsed

Cheers,
-- 
Cameron Simpson <[email protected]>

          "Neomort" : Brain-dead human, kept alive for medical purposes.
"Medicine Lecturer" : Brain-dead human, kept alive for medical purposes.