Some days ago I've replaced cronwrapper, a script to monitor output of cron scripts with the replacement cwrap in's puppet configuration.

If the script prints on stdout, cwrap does not raise an error by default, which cronwrapper did.

To notify every user of the change, I want to send an email to every ex-cronwrapper user.


The configuration is stored in a subversion repo, which I locally sync using git svn. Thus I can use git log -p to see all changes.

A typical line of interest looks like this:

-        command => '/usr/local/bin/ EMAIL@EXAMPLE.COM "[mob][low][dev03-sth][front] description" /usr/bin/php /some/script',

Thanks to git, grep, sed, awk, there is a pretty simple solution (not the most beautiful) to this problem. First of all, get all patches:

git log -p

Then find all removal entries of cronwrapper:

grep ^- | grep cronwrapper

But only those containing an e-mail address:

grep '@'

And filter out the e-mail address:

sed 's/.* \(.*@.*\)/\1/' | awk '{ print $1 }'

Replace all quotes and backslash quotes:

sed -e 's/\\"//g' -e 's/"//g' -e "s/'//g"

The problem now is that some e-mail adresses are indeed multiple e-mail adresses (; and some e-mail adresses are lower, some upper case.

Breaking up the concatenated addresses can be done use awk easily:

awk '{ gsub(";", "\n"); print $0 }'

Transforming all addresses to lower case can be done using the fine utility tr:

tr '[A-Z]' '[a-z]'

Filter out all duplicates:

sort | uniq

The result is a list of e-mail addresses. Making them usable for copy & paste into webmail of exchange needs another filter to convert \n to ;, but add one \n at the end:

awk 'ORS=";" { print $0 } END { ORS="\n"; print "" }' 

So in the end, the complete chanin looks like this:

git log -p | grep ^- | grep cronwrapper | \
grep '@' | sed 's/.* \(.*@.*\)/\1/' | awk '{ print $1 }' | \
sed -e 's/\\"//g' -e 's/"//g' -e "s/'//g" | \
tr '[A-Z]' '[a-z]' | \
awk '{ gsub(";", "\n"); print $0 }' | \
sort | uniq | \
awk 'ORS=";" { print $0 } END { ORS="\n"; print "" }'

For me, this is a nice demonstration of the power of shell, unix tools and filtering via pipes.