using $ARGV without arguments

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

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Re: using $ARGV without arguments by hardburn (Abbot) on Jun 24, 2003 at 14:01 UTC
When you don't pass anything in, `$ARGV[0]` won't be defined. Under `use warnings`, trying to compare an undefined value gives you that (non-fatal) error message. To stop it, first check if `$ARGV[0]` is defined, then do your test: `if( defined($ARGV[0]) && ($ARGV[0] eq 'TEST') ) {` [download] ---- I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident. -- Schemer Note: All code is untested, unless otherwise stated	[reply] [d/l] [select]
Re: using $ARGV without arguments by broquaint (Abbot) on Jun 24, 2003 at 14:01 UTC
Because the 0th element of `@ARGV` is empty and therefore uninitialized. To supress the warning just check if `@ARGV` has been populated e.g `if(@ARGV and $ARGV[0] eq 'TEST') { print "$ARGV[0]\n"; }` [download] See. `perlvar` for more info on `@ARGV`. HTH `_________ broquaint` update: `'pritn' ne 'print'`, thanks to particle	[reply] [d/l]
Re: using $ARGV without arguments by Bilbo (Pilgrim) on Jun 24, 2003 at 14:07 UTC
Well, if you don't put any arguments in then `$ARGV[0]` is undefined. What do you want to do if no arguments are given? Do you want it to cause an error: `unless (@ARGV == 1) { die "You must specify one argument\n"; }` [download] Or do you want to set a default value? `my $argument = $ARGV[0] \|\| 'default' ; # Put your default # value here if ($argument eq 'TEST') {....` [download] Or do you just want it to ignore the argument? `if (defined $ARGV[0] && $ARGV[0] eq 'TEST') {...` [download]	[reply] [d/l] [select]
Amateur Perl Hacker by Arbogast (Monk) on Jun 24, 2003 at 15:26 UTC
Question on acceptable practice. Subject, warning on Use of uninitialized value in string eq at ... When this happens, I go back and check my code to make sure it is OK the value is sometimes unitialized. If it OK, I move on and dont worry about it. Is this a bad habit???	[reply]
Re: Amateur Perl Hacker by hsmyers (Canon) on Jun 25, 2003 at 14:15 UTC
Yes. Lots of Famous Really Good Programmers (tm) will tell you to always initialize vars---but since I'm not one of them, I'll tell you to at least try and make it a habit since it will save you grief later on. My rule is that if there is a chance that I'll check the value before I stuff something in it, I'll usually set it to a known value... --hsm "Never try to teach a pig to sing...it wastes your time and it annoys the pig."	[reply]
Re: using $ARGV without arguments by tcf22 (Priest) on Jun 24, 2003 at 14:05 UTC
You could set it to a blank string if not defined like this `#!/usr/bin/perl use warnings; use strict; $ARGV[0] \|\|= ''; if ($ARGV[0] eq 'TEST') { print "$ARGV[0]\n"; }` [download] or check for it being defined like this `#!/usr/bin/perl use warnings; use strict; if (defined($ARGV[0]) && $ARGV[0] eq 'TEST') { print "$ARGV[0]\n"; }` [download] I prefer the second option.	[reply] [d/l] [select]