You need to specify a 'mode' when you use open. This means that you specify whether you want to read from or write to a particular file (you can do both, but you don't need that for now).

use strict;
use warnings;

my $INPUT;
my $OUTPUT;

open($INPUT, "<", "my_input_file.txt"); #the "<" tells it you want to 
+read from the file
open($OUTPUT, ">" "my_output_file.txt"); #the ">" tells it you want to
+ write to the file.

while(my $line=<$INPUT>){
     #.. do some changes to $line ..
     print $OUTPUT $line #prints $line (after I've done whatever chang
+es) to the file I opened as $OUTPUT
}

[download]

check out here for some more info on filehandles. Also bear in mind that you can either not declare a filehandle, and just use a plain text word, e.g.  open(INPUT,"<","input_file.txt); or you can declare a variable as I did in the example above. IMO it's a better habit to get into to use a variable, as you start to get into trouble when/if you try to pass filehandles around subs (later..!)

hope this helps.
why_bird
........
Those are my principles. If you don't like them I have others.
-- Groucho Marx
.......

In reply to Re^4: a REFERENCE of array of hashes by why_bird
in thread a REFERENCE of array of hashes by fseng

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.