Dual use bash script - source but also exec subshell? Dynamic return/exit?

Question

My current setup starts with a function that is ostensibly in .bashrc (.bash_it/custom/funcs.bash to be precise)

#!/usr/bin/env bash
function proset() {
  . proset-core "$@";
}

proset-core does some decrypting of secrets and exports those secrets to the session, hence the need for the . instead of just running it as a script/subshell.

If something goes wrong in proset-core, I use return instead of exit since I don't want the SSH connection to be dropped.

if [ "${APP_JSON}" = "null" ] ; then
  echo -e "\n${redtext}App named $NAME not found in ${APPCONF}. Aborting.${resettext}\n";
  return;
fi

This makes sense in the context of the exported proset function, but precludes usage as a script since return isn't valid except from within a function.

Is there a way to detect how it's being called and return one or the other as appropriate?

BTW, function funcname() { ... } is bad form -- old-ksh format is function funcname {, POSIX-standard format is funcname() {; the idiom that uses both the function prefix and the () is compatible with neither. See wiki.bash-hackers.org/scripting/obsolete -- if you want to pick one or the other practice to learn, the POSIX-y one is probably better; means you aren't in habits that will make your code break when run in /bin/sh, and won't confuse people used to ancient ksh where function makes variables local-by-default (which it doesn't do in bash). — Charles Duffy
– Charles Duffy, Commented Mar 9, 2018 at 21:06

Charles Duffy · Accepted Answer · 2018-03-09 22:00:38Z

2

Just try to return, and exit if it fails.

_retval=$?
return 2>/dev/null || exit "$_retval"

The only case where your code will still be continuing after the return was invoked at top-level (outside of a function) is if you were executed rather than sourced, and should that happen, exiting is the Right Thing.

answered Mar 9, 2018 at 22:00

Charles Duffy

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1 Comment

Thomas Guyot-Sionnest Over a year ago

BTW you can also declare exit as a function while you source a file to prevent exiting... I use that sometime in shell test scripts to load inline functions then capture the results.

notbrain · Accepted Answer · 2018-03-09 19:45:20Z

1

Make the builtin variable $SHLVL part of $@ args as the last arg. Then at test point:

if [ "${@: -1}" -lt $SHLVL ]; then
    # SHLVL arg is less than current SHLVL
    # we are in a subshell
    exit
else
    return
fi

edited Mar 9, 2018 at 19:45

notbrain

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answered Mar 8, 2018 at 0:55

LMC

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1 Comment

notbrain Over a year ago

Doesn't this require that any other use of proset-core would need to pass $SHLVL all the time? And when "$@" is empty, also detect the number of args and adjust accordingly. Is there a way to check without changing the arg list to proset-core?

notbrain · Accepted Answer · 2018-03-09 21:57:42Z

0

Ended up using

calledBy="$(ps -o comm= $PPID)";
if [ "x${calledBy}" = "xsshd" ]; then
  return 1;
else
  exit 1;
fi

since it didn't require passing anything extra. Anything that might cause this to be problematic please comment. Not too worried about being bash-specific or portable.

Credit: get the name of the caller script in bash script

edited Mar 9, 2018 at 21:57

answered Mar 9, 2018 at 21:51

notbrain

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3 Comments

Charles Duffy Over a year ago

The x$foo is unnecessary here, btw -- [ "$calledBy" = sshd ] is perfectly safe. The only case where that idiom is needed in modern (post-1990) shells is when you're using -a or -o to combine multiple tests in one instance, and POSIX has that syntax marked as obsolescent (search for OB markers in pubs.opengroup.org/onlinepubs/9699919799/utilities/test.html).

Charles Duffy Over a year ago

...that said, this seems like a lot of overhead for a not-particularly-reliable test (whether you were sourced and whether you're a direct subprocess of sshd are really two different questions!).

Charles Duffy Over a year ago

...to provide some concrete examples, you might be sourced into a shell that is a child of gnome-terminal or /bin/login rather than sshd, or someone might run ssh hostname 'exec /path/to/your-script', in which case you'll be a direct child of sshd, but executed and not sourced.

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