Perl Script - find line beginning with X?

Question

Hi,

I need some simple logic for a function that is opening a file and looking for a line beginning with IDX. I already have the code to open the file I just need the search part.

In english something that says next if(not equal to IDX)

Thanks!

Answer 1

!/usr/bin/perl -w

use strict;

open( INFIL, "</foo.txt" ) or die $!;

while( my $lin = <INFIL> ) {

  unless( $lin =~ m@^IDX@ ) { next; }

  // found it!

  last; // if you're only interested in the first one

}

close INFIL;

Answer 2

You can transfer the contents of a file to an array like this:

$FILE = "file.txt";

open (FILE) or die "Can't open the file!";

@fileinput = <FILE>;

then you can use a loop like usual to step through the array and compare the current index to IDX.  

Good luck.

Answer 3

You want a regular expression (regex or regexp).  They can be very in depth, but they're easy once you get the hang of them.  You want something like this:

if(open(FILE,"myfile.txt")) {

  while(<FILE>) {

    if(/^IDX/) {

      #Code here-- your line is in the $_ variable, complete with newline

    }

  }

}

Here, you're doing a test on the $_ variable to see if it matches the regexp /^IDX/.  You can perform that same check on other variables by using something like this:

if($foo =~ /^IDX/) { ... }

The carat is a special character meaning "beginning of line".  So if you wanted instead to search for any line that had "IDX" in it (not just at the front), you'd use /IDX/ instead.  There's a lot to learn about regexes, and they're frequently used in many languages-- many are even based on Perl's style.  So they're good to learn more about!

DaveE