Shell scripts connected with pipe: trap termination of one script

Question

I have two shell scripts, one runs on a server and writes some files to a temporary directory. This directory is then sent as a tar archive to stdout. At the end (or when it gets interrupted), the temporary directory should be deleted. The server script (saved e.g. in '~/get_dumps.sh') looks like this:

#!/bin/sh
set -e
temp_dir=`mktemp -d`
cd $temp_dir
trap "rm -r $temp_dir; exit" HUP INT TERM PIPE
for db in db1 db2 db3
  do
    pg_dump $db postgres > $db.sql
done
tar cJf - .
rm -r $temp_dir

The server script is called from a client with this script:

#!/bin/sh
set -e
temp_dir=`mktemp -d`
trap "rm -r $temp_dir; exit" HUP INT TERM PIPE
mkdir /tmp/dumps
ssh server '~/get_dumps.sh' | tar xJf - -C $temp_dir
ls $temp_dir
rm -r $temp_dir

If I run the client script and press Ctrl-C, neither on the client nor on the server the temporary directories are removed. Why does trap here not work?

Edit: First I have forgotten to add set -e.

Answer 1

The problem was set -e. If one presses e.g. Ctrl-c while mutiple commands are piped together, SIGINT is not sent to the script, but somewhere else. This creates an error which is handled by set -e and so the script exits directly. To use set -e reliable in scripts with pipes, one has to trap also EXIT:

#!/bin/sh
set -e
temp_dir=`mktemp -d`
cd $temp_dir
trap "rm -r $temp_dir; exit" HUP INT TERM PIPE EXIT
 for db in db1 db2 db3
   do
     pg_dump $db postgres > $db.sql
done
tar cJf - .

In this case, also the normal exit is handled by trap, which in many cases is anyway useful.