Bash – Upstart and Bash Function Names Containing Hyphens

bashshellupstart

I inherited some bash scripts where the author used "-" in the function names instead of the more normal "_" e.g.:

function a-b {
...
}

Ugly but legal in bash. Problem is I sourced this inside an upstart script and got

x.sh: line 5: `a-b': not a valid identifier

Took a while to realize it was the name and not the function contents. Anyway, renaming is not an easy option in this case and as I've learned, upstart uses /bin/sh not /bin/bash to parse? run its scripts. Hence I guess this issue.

Any ideas on a workaround other than renaming?

If nothing else, at least I hope this question will warn others on the perils of odd bash coding styles and how they come back to bite you sometimes.

Best Answer

From the Upstart cookbook, Changing the Default Shell. There are 3 options, the first 2 involve changing your default shell from /bin/sh to something else. But the 3rd option looks like it would solve your particular issue.

excerpt

Use a "here document" (assuming your chosen shell supports them) within the Job Configuration Files you wish to run with a different shell:
script
/bin/bash <<EOT

echo "Hi - I am running under the bash shell"

date

echo "and so am I :)"

EOT
end script

Related Solutions

Bash – How to explicitly and safely force the use of a built-in command in bash

Olivier D is almost correct, but you must set POSIXLY_CORRECT=1 before running unset. POSIX has a notion of Special Built-ins, and bash supports this. unset is one such builtin. Search for SPECIAL_BUILTIN in builtins/*.c in the bash source for a list, it includes set, unset, export, eval and source.

$ unset() { echo muahaha-unset; }
$ unset unset
muahaha-unset
$ POSIXLY_CORRECT=1
$ unset unset

The rogue unset has now been removed from the environment, if you unset command, type, builtin then you should be able to proceed, but unset POSIXLY_CORRECT if you are relying on non-POSIX behaviour or advanced bash features.

This does not address aliases though, so you must use \unset to be sure it works in interactive shell (or always, in case expand_aliases is in effect).

For the paranoid, this should fix everything, I think:

POSIXLY_CORRECT=1
\unset -f help read unset
\unset POSIXLY_CORRECT
re='^([a-z:.\[]+):' # =~ is troublesome to escape
while \read cmd; do 
    [[ "$cmd" =~ $re ]] && \unset -f ${BASH_REMATCH[1]}; 
done < <( \help -s "*" )

(while, do, done and [[ are reserved words and don't need precautions.) Note we are using unset -f to be sure to unset functions, although variables and functions share the same namespace it's possible for both to exist simultaneously (thanks to Etan Reisner) in which case unset-ing twice would also do the trick. You can mark a function readonly, bash does not prevent you unsetting a readonly function up to and including bash-4.2, bash-4.3 does prevent you but it still honours the special builtins when POSIXLY_CORRECT is set.

A readonly POSIXLY_CORRECT is not a real problem, this is not a boolean or flag its presence enables POSIX mode, so if it exists as a readonly you can rely on POSIX features, even if the value is empty or 0. You'll simply need to unset problematic functions a different way than above, perhaps with some cut-and-paste:

\help -s "*" | while IFS=": " read cmd junk; do echo \\unset -f $cmd; done

(and ignore any errors) or engage in some other scriptobatics.

Other notes:

function is a reserved word, it can be aliased but not overridden with a function. (Aliasing function is mildly troublesome because \function is not acceptable as a way of bypassing it)
[[, ]] are reserved words, they can be aliased (which will be ignored) but not overridden with a function (though functions can be so named)
(( is not a valid name for a function, nor an alias

Bash – How to call bash function from within awk

You may be able to do what you want by piping awk's output into a while read loop. For example:

awk '/^#/ {next}; NF == 0 {next}; NF != 4 {exit 1} ; {print}' | 
    while read NAME METHOD URL TAG ; do
        :  # do stuff with $NAME, $METHOD, $URL, $TAG
        echo "$NAME:$METHOD:$URL:$TAG"
    done

if [ "$PIPESTATUS" -eq 1 ] ; then
    : # do something to handle awk's exit code
fi

Tested with:

$ cat input.txt 
# comment
NAME METHOD URL TAG
a b c d
1 2 3 4
x y z
a b c d

$ ./testawk.sh <input.txt 
NAME:METHOD:URL:TAG
a:b:c:d
1:2:3:4

Note that it correctly exits on the fifth x y z input line.

Best Answer

Related Solutions

Bash – How to explicitly and safely force the use of a built-in command in bash

Bash – How to call bash function from within awk

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