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From: lwall@jpl-devvax.jpl.nasa.gov (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: Checking if a variable is null
Keywords: perl null
Message-ID: <1991Apr19.214729.14908@jpl-devvax.jpl.nasa.gov>
Date: 19 Apr 91 21:47:29 GMT
References: <483@cti1.UUCP>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 38

In article <483@cti1.UUCP> kmeek@cti1.UUCP (Kevin Meek) writes:
: Is there a perl equivalent to the shell test operators -z and -n 

Not in so many tokens, but there are already lots of ways to do that.

: I want to print a line if certain parts are not null.
: 
: What I'm using is this:
: 
: ($a,$b,$c) = split(' ');
: if ( $a ne '' && $b ne '' ) {
:    print $_;
: }
: 
: Is there a better way to check if a variable is null?
: i.e. print if -n $a 
: 
: Also I wanted to get it into a oneliner but when I have a multi part
: expression (i.e. EXPR && EXPR), I had trouble getting the 
: print if EXPR construct to work.  

You should be able to say

	($a,$b) = split(' ');
	print if $a ne '' && $b ne '';

That's valid, syntactically.  However, split on arbitrary whitespace can
never return a null field followed by a non-null field, if you think about it.
Any two adjacent delimiter fields are treated as a single delimiter field,
and everything just shifts down.  Either you need a specific delimiter like
a single space or tab, or you should be treating the fields as fixed-length
(in which case, use unpack with A fields).

In any event, you can probably do your one-liner easier with a regular
expression.  It's difficult to give the exact expression without knowing more
about the problem.

Larry