if statement comparing elements of arrays?

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

Hello PerlMonks I am looking to determine why an 'if' statement is failing. I am using it to compare elements of the 2 arrays. I have it working for the first elements of the arrays but not for the remainder even though when I print the offending elements they look the same. Any perls of wisdom?? .. code below...

#compare the commands in the arrays
if (($commands_run[0] =~ /$commands[0]/)
&&($commands_run[1] =~ /$commands[1]/)
&&($commands_run[2] =~ /$commands[2]/)
&&($commands_run[3] =~ /$commands[3]/)
&&($commands_run[4] =~ /$commands[4]/))
{
print "Test -----PASS\n";
}
else
{
print "Test ---- FAIL\n";
}
[download]

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Re: if statement comparing elements of arrays? by Corion (Patriarch) on Jul 14, 2009 at 09:29 UTC
How do you print them? If there is whitespace at the start or end, they will look similar but still won't run. Also, are you sure that `@commands` contains regular expressions that will match? Do something like the following: `for my $i (0..$#$commands_run) { print "$i: '$commands_run[$i]' =~ /$commands[$i]/"; print $commands_run[$i] =~ /$commands[$i]/ ? ", Yes" : ", No"; print "\n"; };` [download] That should give you a good overview. Also, you might want to consider instead of having that long `if` statement using a loop similar to the one I showed for the actual testing. This will also help you to provide better diagnostic output if your test fails, as you can show which condition failed.	[reply] [d/l] [select]
Re: if statement comparing elements of arrays? by JavaFan (Canon) on Jul 14, 2009 at 09:46 UTC
Are the elements of @commands supposed to be patterns? Or do you want exact matches (use `eq`)? Or perhaps check for a substring (use `index`)? Because if you want to do either of them, and one or more of the commands contain something that is special to the regexp engine (parens, *, +, etc), it isn't going to work.	[reply] [d/l] [select]
Re: if statement comparing elements of arrays? by ikegami (Patriarch) on Jul 14, 2009 at 15:00 UTC
I bet that `@commands` does not contain regex patterns, but you treat its contents as such. `=~ /$commands[0]/ # Matches pattern in $commands[0] =~ /\Q$commands[0]\E/ # Contains string in $commands[0] =~ /^\Q$commands[0]\E\z/ # Equals string in $commands[0] eq $commands[0] # Equals string in $commands[0]` [download] `\Q..\E` is a shortcut for calling `quotemeta`. And here's a solution that avoids redundancy: `if ( grep { $commands_run[$_] ne $commands[$_] } 0..$#commands ) { print "Test ---- FAIL\n"; } else { print "Test -----PASS\n"; }` [download]	[reply] [d/l] [select]
Re: if statement comparing elements of arrays? by si_lence (Deacon) on Jul 14, 2009 at 09:32 UTC
Your code works for me `use strict; use warnings; #compare the commands in the arrays my @commands_run = qw(first second third fourth fifth); my @commands = qw(first second third fourth fifth); if (($commands_run[0] =~ /$commands[0]/) &&($commands_run[1] =~ /$commands[1]/) &&($commands_run[2] =~ /$commands[2]/) &&($commands_run[3] =~ /$commands[3]/) &&($commands_run[4] =~ /$commands[4]/)) { print "Test -----PASS\n"; } else { print "Test ---- FAIL\n"; }` [download] prints `Test -----PASS` [download] So maybe your two arrays are not the same after all. Maybe print them with Data::Dumper to confirm? Cheers, si_lence	[reply] [d/l] [select]
Re: if statement comparing elements of arrays? by jeanluca (Deacon) on Jul 14, 2009 at 11:16 UTC
it might help to inspect your arrays with Data::Dumper `use Data::Dumper ; my @arr = qw(1 2 3 4 5) ; print Dumper(\@arr) ;` [download]	[reply] [d/l]