Checking If Unix Parameter is Non-Empty [duplicate]

Question

Possible Duplicate:
How to tell if a string is not defined in a bash shell script?
What’s the best way to check that environment variables are set in Unix shellscript

I'm trying my hand at Unix shell scripting for the first time and in a script I'm working on now, I want 2 of the 3 arguments to my script to be optional. However, if the user doesn't enter the arguments, I need to use default values. How can I properly say something that basically means:

$argument = $2
if($argument  == "")
    $argument = "defaultVal"

Thanks!

I thought $# stored the number of input params? I could be wrong. — TheZ
– TheZ, Commented Oct 18, 2012 at 19:57
Possible duplicate of What's the best way to check that environment variables are set in Unix shellscript, or you might prefer How to tell if a string is not defined in a Bash shell script — Jonathan Leffler
– Jonathan Leffler, Commented Oct 18, 2012 at 20:17

William Pursell · Accepted Answer · 2012-10-18 19:59:10Z

2

try:

argument=${2:-default value}

answered Oct 18, 2012 at 19:59

William Pursell

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1 Comment

JToland Over a year ago

Both these answers seem to work great - I just accepted the first one I got working! Thanks to both of you for your quick replies!

user529758 · Accepted Answer · 2012-10-18 19:58:00Z

1

Try this:

if [ "x$2" == "x" ]; then
    $argument="default";
else
    $argument=$2;
fi

answered Oct 18, 2012 at 19:58

user529758

3 Comments

chepner Over a year ago

Is that trick still necessary? if [ "$2" = "" ]; works fine, in bash and dash at least.

user529758 Over a year ago

@chepner I had problems with the "" being recognized as an empty token producing a syntax error, so I'd say yes.

JToland Over a year ago

Both these answers seem to work great - I just accepted the first one I got working! Thanks to both of you for your quick replies!

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