pipe only if exit status is oK

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> grep xxx myfile > myfile.tmp
> [ $? -eq 0 ] && cat myfile.tmp | mail someone
>
> Of course the following doesnt work but I hope there is a trick to write
> something like
> grep xxx myfile &&| mail someone
>
> "mail" is just an example. So I dont need special switches for the
> mail-command, it is a shell question:
> How to activate a pipe only if the exit status of the former command has
> been oK.

I think the nearest is something like…

grep xxx myfile > myfile.tmp && cat myfile.tmp | mail someone

Example 1. ..or maybe…

grep xxx myfile && grep xxx myfile | mail someone

..if you don't want to create a "tmp" file. Adrian

pipe only if exit status is oK

One way to do it would be the following:

oIFS=$IFS;IFS=''
RESULT=$(grep xxx myfile)
[[ ! -z "$RESULT" ]] && echo $RESULT | mail someone
IFS=$oIFS

That only works if (like grep) if the command fails and produces no output. You could change that to:

oIFS=$IFS;IFS=''
RESULT=$(grep xxx myfile)
[[ "$?" == 0 ]] && echo $RESULT | mail someone
IFS=$oIFS

This might work also:

grep xxx myfile | ( [[ $? == 0 ]] && mail someone )

Be aware that that will run the mail command in a subshell (but you may not notice any difference if you use bash - bash runs the last command in a pipeline in a subshell anyway). What difference does that make? Well, consider he following:

grep xxx myfile | ( [[ $? == 0 ]] && mail someone || echo "Nothing found" )

You might reasonably expect the command to print out "Nothing found" if grep fails to find a match. It in fact produces no output since the echo prints to the subshell. The best way to achieve conditional piping (of a sort) is to use redirections as a kind of 'pipe emulator'. Search http://deja.com/ in comp.unix.shell for the subject "conditional piping" for previous discussions.

Dave. :-)

documented on: 2000.08.31 Thu 00:53:39