take input from command prompt in perl

Question

I am trying to write a script in which I should open a file that can be any file.

But I want to pass the name of file from the command prompt or some other way, so that I don't have to edit the script when ever the input file name changes.

Can any one help how can I do that ?

        open (DBC, "test.txt")|| die "cant open dbc $!";
        @dbc =  <DBC>;
        close (DBC);

the file is in the directory where my script is, that's why am not giving any path here

Answer 1

You want to use the ARGV array for getting, say, the first argument:

my $file = $ARGV[0];
open (DBC, $file)|| die "cant open dbc $!";
@dbc =  <DBC>;
close (DBC);

There are a lot of better ways to eventually do this sort of thing, like checking to make sure they passed something first:

if ($#ARGV == -1) {
    die "You need to supply a file name to the command";
}

my $file = $ARGV[0];
open (DBC, $file)|| die "cant open dbc $!";
@dbc =  <DBC>;
close (DBC);

And you can go on from there, eventually learning about the Getopt::Long and similar modules.

Answer 2

Read perlop #I/O Operators for a shortcut method for processing files passed from the command line. To briefly quote from the linked documentation:

The null filehandle <> is special: it can be used to emulate the behavior of sed and awk, and any other Unix filter program that takes a list of filenames, doing the same to each line of input from all of them. Input from <> comes either from standard input, or from each file listed on the command line. Here's how it works: the first time <> is evaluated, the @ARGV array is checked, and if it is empty, $ARGV[0] is set to "-", which when opened gives you standard input. The @ARGV array is then processed as a list of filenames.

Basically, you can simplify your script to just the following:

use strict;
use warnings;

die "$0: No filename specified\n" if @ARGV != 1;

while (<>) {
    # Process your file line by line.

}