Shell script - check the syntax

Question

How to check the correctness of the syntax contained in the ksh shell script without executing it? To make my point clear: in perl we can execute the command:

perl -c test_script.pl

to check the syntax. Is something similar to this available in ksh?

Gilbert · Accepted Answer · 2011-08-22 10:00:51Z

4

ksh -n

Most of the Borne Shell family accepts -n. tcsh as well.

answered Aug 22, 2011 at 10:00

Gilbert

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5 Comments

sachin Over a year ago

It does not seem to be working. I executed ksh -n test.sh but it did not list out the syntax error which was there in test.sh

Jens Over a year ago

Yes it does work. I'm sure there is no syntax error. If you show us the script we can analyze if your expectations of finding a syntax error are correct.

tripleee Over a year ago

Then try with sh -n script. It should work. However, if your syntax error is in an invalid command name, that would only get caught at run time. sh -n only checks the actual shell syntax.

Gilbert Over a year ago

Also some errors only show up at run time, even syntax errors. The trouble is that shells reparse each line each time the line executes... a classic "interpreter" behavior. Thus if any meta-characters (' " $, ... often ! ... ) are in a variable used in the line the characters can adversely impact late parsing. The first round of defense is to quote every $ variable, and if reading $*, understand and use the alternate "$@" notation (with the double quotes).

AdOracle Over a year ago

Jens : yes -n did not catch syntax errors like I changed echo to eco and sh -n did not report any syntax error

immnek · Accepted Answer · 2015-03-03 09:38:03Z

1

I did a small test with the following code:

#!/bin/bash
if [ -f "buggyScript.sh" ; then
    echo "found this buggy script"
fi

Note the missing ] in the if. Now I entered

bash -n buggyScript.sh

and the missing ] was not detected.

The second test script looked like this:

#!/bin/bash
if [ -f "buggyScript.sh" ]; then
    echo "found this buggy script"

Note the missing fi at at end of the if. Testing this with

bash -n buggyScript.sh

returned

buggyScript.sh: line 5: syntax error: unexpected end of file

Conclusion: Testing the script with the n option detects some errors, but by no means all of them. So I guess you really find all error only while executing the script.

answered Mar 3, 2015 at 9:38

immnek

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Comments

Noj · Accepted Answer · 2016-06-08 14:36:37Z

1

The tests that you say failed to detect syntax errors, where not in fact syntax errors... echo is a command (OK a builtin, but still a command) so ksh/bash are not going to check the spelling/syntax of your command. Similarly "[" is effectively an alias for the test command, and the command expects the closing brace "]" as part of its syntax, not ksh/bash's. So -n does what it says on the tin, you just haven't read the tin correctly! :-)

answered Jun 8, 2016 at 14:36

Noj

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