1

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.

Improve this question
6
  • Works fine for me. What OS & shell are you using (/bin/sh)? What point is the script at when you CTRL+C it? Have you tried running the script with debug output (set -x)? Commented Apr 19, 2017 at 4:26
  • @Patrick I'm using Ubuntu 16.04 with dash. Thank you for the hint set -x. In the local test scripts, I had included set -e and forgotten to add it to the example code above. With set -x or without set it works. It seams that set -e is incompatible with trap. Commented Apr 19, 2017 at 6:27
  • @FabianHeller set -e is not incompatible with trap. Where does the script(s) terminate if you use set -e? Commented Apr 19, 2017 at 7:12
  • @Kusalananda I can press Ctrl-C on the client side either when the server script is executing pg_dump or tar. With or without set -e, the result is in both cases the same: The execution of pg_dump or tar stops immediately (and the script exits directly after pg_dump or tar). With set -e(x), trap is not called, with set -x (or without set) it works as intended. Commented Apr 19, 2017 at 9:13
  • @FabianHeller First you say that it doesn't work with or without set -e. Then you say it works without set -e. Confused. Commented Apr 19, 2017 at 10:07

1 Answer 1

Reset to default
0

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.

Improve this answer

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.