In any UNIX-like shell, when you specify a filename glob (i.e. a filename with wildcards) on the shell commandline, it is the shell, and not the program you are calling, which expands the glob.

So yes, when you call

rename.pl *.txt

If you want the script to do the glob expansion, you'd have to enclose the argument in single quotes, i.e. call it like this:

somescript.pl '*.txt'

Then the Perl script finds exactly one arg in @ARGV, namely *.txt and you would have to find some way to do the expansion.

With Larry's script however, I typically feed it ALL the files by matching *; it will only act on those files which max the regexp given as the first argument anyway, all others are skipped. Of course that requires some care in constructing the regexp.

@ARGV would be an Array with four entries like this right?

use strict;
use warnings;

print "These are the ", scalar @ARGV, " arguments:\n";
my $i = 0;
for (@ARGV) {
    print "ARGV[$i] = $_\n";
    $i++;
}
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prints:

These are the 4 arguments:
ARGV[0] = s/foo/bar/
ARGV[1] = file1.txt
ARGV[2] = file2.txt
ARGV[3] = file3.txt
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Alternately, you can use Data::Dumper:

use strict;
use warnings;
use Data::Dumper;
print Dumper(\@ARGV);
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prints:

$VAR1 = [
          's/foo/bar/',
          'file1.txt',
          'file2.txt',
          'file3.txt'
        ];
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What I do not understand is how the script determines which files to put into @ARGV. At which point is "*.txt" being evaluated? Or is it the shell that tells the script which files in the directory match the pattern *.txt?

use strict;
use warnings;

my $op = shift;
# same as: my $op = shift @ARGV;

print "These are the ", scalar @ARGV, " arguments:\n";
my $i = 0;
for (@ARGV) {
    print "ARGV[$i] = $_\n";
    $i++;
}
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prints:

These are the 3 arguments:
ARGV[0] = file1.txt
ARGV[1] = file2.txt
ARGV[2] = file3.txt
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Hi toolic,

thank you for your quick reply. I understand what shift does in this script. What I don't understand is how all txt files in the directory end up in @ARGV.

When I copy and paste your code, what I get is:

These are the 2 arguments:
ARGV[0] = s/\.txt\.mex//
ARGV[1] = *.txt
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And this also makes sense to me, because how would the script be able to know which files in the directory match '*.txt'? Doesn't there have to be another process that matches '*.txt' against all files in the directory first?

Arian

When I copy and paste your code

Since I provided 3 sets of code and output data, I am not sure which one you ran.

Let's try another approach...

> ls *.txt
file1.txt  file2.txt  file3.txt
> cat test.pl
#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;
print Dumper(\@ARGV);
> ./test.pl 's/foo/bar/' file*.txt
$VAR1 = [
          's/foo/bar/',
          'file1.txt',
          'file2.txt',
          'file3.txt'
        ];
>
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My operating system in Linux. I have 3 *.txt files in my current directory. When I run my test.pl script, it simply prints out the contents of the @ARGV array, which correspond to the things which appear on the test.pl command line. The 1st thing on the command line is the string corresponding to the substitution operator. The 2nd thing on the command line is a file specifier using the standard Unix wildcard character (*), which gets expanded into 3 filenames.

Are you on a *nix OS, or are you on Windows, or a Mac?

Are you familiar with the concept of wildcard expansion?

sorry for the mistake in the 's///' bit, but it doesn't change the result