• Uncategorized

About linux : How-do-I-syntax-check-a-Bash-script-without-running-it

Question Detail

Is it possible to check a bash script syntax without executing it?

Using Perl, I can run perl -c 'script name'. Is there any equivalent command for bash scripts?

Question Answer

bash -n scriptname

Perhaps an obvious caveat: this validates syntax but won’t check if your bash script tries to execute a command that isn’t in your path, like ech hello instead of echo hello.

Time changes everything. Here is a web site which provide online syntax checking for shell script.

I found it is very powerful detecting common errors.

About ShellCheck

ShellCheck is a static analysis and linting tool for sh/bash scripts. It’s mainly focused on handling typical beginner and intermediate level syntax errors and pitfalls where the shell just gives a cryptic error message or strange behavior, but it also reports on a few more advanced issues where corner cases can cause delayed failures.

Haskell source code is available on GitHub!

I also enable the ‘u’ option on every bash script I write in order to do some extra checking:

set -u 

This will report the usage of uninitialized variables, like in the following script ‘check_init.sh’

set -u
echo $mesage

Running the script :

$ check_init.sh

Will report the following :

./check_init.sh[4]: mesage: Parameter not set.

Very useful to catch typos

sh  -n   script-name 

Run this. If there are any syntax errors in the script, then it returns the same error message.
If there are no errors, then it comes out without giving any message. You can check immediately by using echo $?, which will return 0 confirming successful without any mistake.

It worked for me well. I ran on Linux OS, Bash Shell.

I actually check all bash scripts in current dir for syntax errors WITHOUT running them using find tool:


find . -name '*.sh' -print0 | xargs -0 -P"$(nproc)" -I{} bash -n "{}"

If you want to use it for a single file, just edit the wildcard with the name of the file.

null command [colon] also useful when debugging to see variable’s value

set -x
for i in {1..10}; do
    let i=i+1
    : i=$i
set - 

For only validating syntax:

shellcheck [programPath]

For running the program only if syntax passes, so debugging both syntax and execution:

shellproof [programPath]

Bash shell scripts will run a syntax check if you enable syntax checking with

set -o noexec

if you want to turn off syntax checking

set +o noexec

There is BashSupport plugin for IntelliJ IDEA which checks the syntax.

If you need in a variable the validity of all the files in a directory (git pre-commit hook, build lint script), you can catch the stderr output of the “sh -n” or “bash -n” commands (see other answers) in a variable, and have a “if/else” based on that

bashErrLines=$(find bin/ -type f -name '*.sh' -exec sh -n {} \;  2>&1 > /dev/null)
  if [ "$bashErrLines" != "" ]; then 
   # at least one sh file in the bin dir has a syntax error
   echo $bashErrLines; 

Change “sh” with “bash” depending on your needs

You may also like...

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.