Let's say you have a shell script that runs some sort of cleanup code
via an EXIT trap, like this:
#!/bin/bash
mytrap () {
echo "It's a trap!" >&2
}
trap mytrap exit
echo I am at the end of the script.
This will, as expected, print out It's a trap! when the script
exits:
$ sh myscript
I am at the end of the script.
It's a trap!
You modify the script to add a function that generates some output that ultimately gets piped to another command, like this:
#!/bin/bash
mytrap () {
echo "It's a trap!" >&2
}
myfunc () {
echo "I've got a bad feeling about this..."
}
trap mytrap exit
myfunc | cat > /dev/null
echo I am at the end of the script.
Because of the pipe, the code in myfunc is run in a subshell...and
subshells don't appear to inherit the trap behavior of the parent,
which means if you perform any actions here that should be cleaned up
by your trap code that won't happen.
So you try this:
myfunc () {
trap mytrap EXIT
echo "I've got a bad feeling about this..."
}
And it still fails to trigger mytrap when the subshell exits. It
turns out that you need an explicit exit, like this:
myfunc () {
trap mytrap EXIT
echo "I've got a bad feeling about this..."
exit
}
With the above code, mytrap will trigger appropriately upon exit
from the subshell:
$ sh myscript
It's a trap!
I am at the end of the script.
It's a trap!
Is that expected behavior? I was surprised by several things here:
trapsettings weren't inherited by subshells- implicit exit from a subshell does not appear to trigger an
EXITtrap
