print specific INFILE area using perl - perl

Question

I have a file with the format below
locale,English,en_AU,6251
locale,French,fr_BE,25477
charmap,English,EN,5423
And I would like to use perl to print out something with the option "-a" follows by the file and outputs something like
Available locales:
en_Au
fr_BE
EN
To do that, I have the perl script below
$o = $ARGV[0];
$f = $ARGV[1];
open (INFILE, "<$f") or die "error";
my $line = <INFILE>;
my #fields = split(',', $line);
if($o eq "-a"){
if(!$fields[2]){print "No locales available\n";}
else{print "Available locales: \n";
while($fields[2]){print "$fields[2]\n";}
}
}
close(INFILE);
And I have three questions here.
1. my script will only print the first locale "en_Au" forever.
2. it should be able to test if a file is empty, but if a file is purely empty, it outputs nothing, but if I type in two empty lines in the file, it prints two lines of "No locales available" instead.
3.In fact in the (!$filed[2]) part I should verify if the file is empty or no available locales exist, if so do I need to put some regular expression here to verify if it is a locale as well??
Hope someone could help me figure these out! Many thanks!!!

Answer 1

The biggest missing thing is a loop over lines from the file, in which you then process one line at a time. Comments follow the code.
use warnings;
use strict;
use feature 'say';
use Getopt::Long;
#my ($opt, $file) = #ARGV; # better use a module
my ($opt, $file);
Getoptions( 'a' => \$opt, 'file=s' => \$file ) or usage();
usage() if not $file; # mandatory argument
open my $fh, '<', $file or die "Can't open $file: $!";
while (my $line = <$fh>) {
chomp $line;
my #fields = split /,/, $line;
next if not $fields[2];
if ($opt) {
say $fields[2];
}
}
close $fh;
sub usage {
say STDERR "Usage: $0 [-a] --file filename";
exit 1;
}
This prints the desired output. (Is that simple condition on $fields[2] really all you need?)
Comments
Always have use warnings; and use strict; at the beginning
I do not recommend single-letter variable names. One forgets what they mean, it makes the code harder to follow, and it's way too easy to make silly mistakes
The #ARGV can be assigned to variables in a list. Much better, use Getopt::Long module, which checks invocation and allows for far easier interface changes. I set the -a option to act as a "flag," so it just sets a variable ($opt) if it's given. If that should have possible values instead, use 'a=s' => \$opt and check for a value.
Use lexical filehandles and the three-argument open, open my $fh, '<', $file ...
When die-ing print the error, die "... $!";, using $! variable
The "diamond" (angle) operator, <$fh>, reads one line from a file opened with $fh when used in scalar context, as in $line = <$fh>. It advances a pointer in the file as it reads a line so the next time it's used it returns the next line. If you use it in list context then it returns all lines, but when you process a file you normally want to go line by line.
Some of the described logic and requirements aren't clear to me, but hopefully the code above is going to be easier to adjust as needed.