Removing created temp files in unexpected bash exit

You could set a "trap" to execute on exit or on a control-c to clean up.

trap '{ rm -f -- "$LOCKFILE"; }' EXIT

Alternatively, one of my favourite unix-isms is to open a file, and then delete it while you still have it open. The file stays on the file system and you can read and write it, but as soon as your program exits, the file goes away. Not sure how you'd do that in bash, though.

BTW: One argument I'll give in favour of mktemp instead of using your own solution: if the user anticipates your program is going to create huge temporary files, he might want set TMPDIR to somewhere bigger, like /var/tmp. mktemp recognizes that, your hand-rolled solution (second option) doesn't. I frequently use TMPDIR=/var/tmp gvim -d foo bar, for instance.

I usually create a directory in which to place all my temporary files, and then immediately after, create an EXIT handler to clean up this directory when the script exits.

MYTMPDIR="$(mktemp -d)"
trap 'rm -rf -- "$MYTMPDIR"' EXIT

If you put all your temporary files under $MYTMPDIR, then they will all be deleted when your script exits in most circumstances. Killing a process with SIGKILL (kill -9) kills the process right away though, so your EXIT handler won't run in that case.