/bin/sh built-in "trap", can't be piped

[Seeker]

Why this doesn't work?

trap 'echo LooooooL!!!' 2
trap | grep .

# This is ok
trap

 

[Seeker]

This will work

...

fname=trap.txt

trap > "$fname"

echo "Listing $fname contest:"
cat "$fname"

rm "$fname"

 

[jilles@]

Anything can be piped but it will run in a subshell environment so that commands like trap will not print what you may expect. (POSIX allows but does not require this.) In our sh, you can do

traps=$(trap)

and it will return the parent shell environment's traps; this commonly works but is not ubiquitous.

 

[Seeker]

That workaround works.