Bash: executing su -c breaks $@

bashshell-scriptsu

Bash version: GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)

This works fine:

#!/bin/bash
exec /usr/local/bin/python2.7 /app/add_container_host.py $@

But I need to run it as a certain user, so I've changed it to:

#!/bin/bash
su -c '/usr/local/bin/python2.7 /app/add_container_host.py $@' $USER

and the Python script is no longer getting the arguments.

I've tried changing the single-quote to double quote and that's supplying the $@ to su -c itself, not to the Python script.

Is there a way to pass $@ to the python script while running it as su -c?

Best Answer

Your issue is the quotes you're using. You need to use double quotes so that the variables within, $@, can be expanded, otherwise they'll remain literals and never get expanded.

Here's an example

$ cat runme.bash
#!/bin/bash

echo "run with double quotes"
su -c "echo $@" user1

echo "run with single quotes"
su -c 'echo $@' user1

$ ./runme.bash "a b c"
run with double quotes
a b c
run with single quotes

$

You also have to pass the list of arguments in as a quoted list, otherwise the su -c ... command gets confused and starts trying to parse the 2nd argument as the user that you want to su as.

Another example

$ ./runme.bash a b c
run with double quotes
su: user b does not exist
run with single quotes

$

Debugging tip

If you want to see what the script is actually doing you can run it with the -x switch to bash.

bare arguments

$ bash -x ./runme.bash a b c
+ echo 'run with double quotes'
run with double quotes
+ su -c 'echo a' b c user1
su: user b does not exist
+ echo 'run with single quotes'
run with single quotes
+ su -c 'echo $@' user1

$

quoted arguments

$ bash -x ./runme.bash "a b c"
+ echo 'run with double quotes'
run with double quotes
+ su -c 'echo a b c' user1
a b c
+ echo 'run with single quotes'
run with single quotes
+ su -c 'echo $@' user1

$

Related Solutions

Bash – Errors with git alias shell command

man git-config says:

The syntax is fairly flexible and permissive; whitespaces are mostly ignored. The # and ; characters begin comments to the end of line, blank lines are ignored.

So:

branch-excise = !bash -c 'git branch -D $1; git push origin --delete $1'

is an equivalent to:

#!/usr/bin/env bash

bash -c 'git branch -D $1

Running the above script prints:

/tmp/quote.sh: line 3: unexpected EOF while looking for matching `''
/tmp/quote.sh: line 4: syntax error: unexpected end of file

One solution is to put a whole command in ":

branch-excise = !"bash -c 'git branch -D $1; git push origin --delete $1'"

However, it still doesn't work because $1 is empty:

$ git branch-excise master
fatal: branch name required
fatal: --delete doesn't make sense without any refs

In order to make it work you need to create a dummy function in .gitconfig and call it like this:

branch-excise = ! "ddd () { git branch -D $1; git push origin --delete $1; }; ddd"

Usage:

$ git branch-excise  master
error: Cannot delete the branch 'master' which you are currently on.
(...)

Bash – If “bash ” works, why is “source ” throwing an error

I can reproduce your behaviour if I alias fi:

$ alias fi=:
+ alias fi=:
$ . ./test
+ . ./test
++ set -x
bash: ./test: line 6: syntax error: unexpected end of file

It works when you execute it but fails when you source it because aliases are not available in non-interactive shells (the type of shell that runs shell scripts). As explained in the bash manual:

Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt (see The Shopt Builtin).

However, when you source something, it is run in your current shell which, because it is interactive, has already loaded the aliases and therefore the fi alias is recognized and breaks the sourcing.