How do I test to see if a variable is set in a script?

[Rex Pommier]

Hi. I have done some earchng of the forums and can't find the answer to this. Within a script, how do I check to see if a variable has been initialised?

TIA

Rex

[Doug O'Leary · Accepted solution]

Hey;

You *should* be able to use the -z or -s switch to test to verify string length:

[[ -z "${var}" ]] && echo "string is zero length"
[[ -s "${var}" ]] && echo "String has a length"

I've had mixed results with that in the past, however. What I normally do is:

[[ "${var}x" = "x" ]] && echo "\${var} not set" || echo "\${var} is set"

HTH;

Doug

[James R. Ferguson]

Hi Rex:

I assume that you mean "in a shell script". If so, you can test with "-z". For instance:

#/usr/bin/sh
[ -z "${X}" ] && echo Empty!

...echo appropriately if the variable is empty.

Be sure to enclose the variable in double quotes to avoid syntatic failures at runtime.

Regards!

...JRF...

[Rodney Hills]

How about-

if set | grep -q "^x=" ; then echo "x has been initialized" ; fi

HTH

-- Rod Hills

[Rex Pommier]

Thanks for the responses. I was able to use them to get it working. Doug and James, I was able to use your suggestions, with the addition of wrapping them with a "set +u" and "set -u", otherwise I got the dreaded "parameter not set" error.

Rodney, I saw your suggestion and had one of those "duh" moments where I realised I was too busy looking for the trees to see the forest. Yours was the suggestion I decided to go with.

Thanks all for your quick responses.

Rex

[Rex Pommier]

All the solutions worked for what I was trying to do.