[Help-bash] Why`trap DEBUG` has no effect if it is called inside a function?

[Peng Yu]

Hi,

The following examples show that if `trap DEBUG` is called inside the
function resetdebugsig, it will not able to reset the DEBUG signal
outside the function. However, this problem does not exist for the
signal EXIT. Can anybody help me understand why there is a difference
between DEBUG and EXIT in this aspect?

~$ cat main.sh
#!/usr/bin/env bash

function resetdebugsig {
trap DEBUG
}
trap 'echo "bash>" "$BASH_COMMAND"' DEBUG
echo abc
resetdebugsig
echo xyz
~$ cat main1.sh
#!/usr/bin/env bash

trap 'echo "bash>" "$BASH_COMMAND"' DEBUG
echo abc
trap DEBUG
echo xyz
~$ ./main.sh
bash> echo abc
abc
bash> resetdebugsig
bash> echo xyz
xyz
~$ ./main1.sh
bash> echo abc
abc
bash> trap DEBUG
xyz
~/EXIT$ cat main.sh
#!/usr/bin/env bash

function resetexitsig {
trap EXIT
}
trap 'echo "$0 is exiting ..."' EXIT
resetexitsig
~/EXIT$ cat main1.sh
#!/usr/bin/env bash

trap 'echo "$0 is exiting ..."' EXIT
trap EXIT
~/EXIT$ ./main.sh
~/EXIT$ ./main1.sh

-- 
Regards,
Peng