How do I check a bash script without running the script?

Question

How do i check for errors (and maybe warnings) in a bash script?

I want to precheck bash scripts before checking them into a git repository.

I know I can use bash -n script.sh for a first, simple check but this doen't find for example things like rewriting on a readonly string.

readonly unique_id = "42"
unique_id = "21"

will be ok for a bash -n script.sh but will fail on execution of course.

EDIT: the following script

#!/bin/bash
# check.sh
readonly unique_id="42"
unique_id="21"

give 0 if you execute bash -n check.sh; echo $? but execution itself results in the error message ./check.sh: line 4: unique_id: readonly variable

Both behaviors are correct because this is not a syntax error but it will still break execution (even in unit tests) and I am asking if there is another way of precheck to filter out such errors.

Unittest will find only expected logical failures so this is not an alternative.

The two lines posted above are *erroneous*. You need to remove spaces surrounding `=`. — devnull, Aug 12 '13 at 08:57
Yep, you are right; I removed the blanks and add a shebang to get a real world example. Thanks — user762353, Aug 16 '13 at 06:18

score 0 · Answer 1 · answered Aug 12 '13 at 08:51

I assume you consider just run that script to check for errors? Then, if you wouldn't do some "errors" message to stdout, you could also check for last exit status code in bash: $?. (http://blog.yimingliu.com/2009/01/01/check-last-exit-status-code-in-bash-shell/)

score 0 · Answer 2 · answered Aug 12 '13 at 09:46

Another way is to place all your codes inside functions. That way you would be able to run your code and check for syntax errors before calling the main function:

#!/bin/bash

function A {
    ...
}

function B {
    ...
}

function main {
    # most of your codes here
    ...
}

# main "$@"

Uncomment the last line if no syntax errors were found. Of course there are exemptions like those executed on eval, nested paramater expansions or expansions basing on a runtime value, some which are based on arguments to a builtin command, and other errors found during runtime.

But you still execute the code... – Bernhard Aug 12 '13 at 10:29 — Bernhard, Aug 12 '13 at 10:29

How do I check a bash script without running the script?

2 Answers2