how can i modify a text file by perl

Question

I want to make 'find/change' function.

1. open original file.

2. change some words through using s/ / / or tr/ / / but it's not working, i think.

    open(TXT, ">>text.txt"); my $str = <TXT>; $str =~ s/'a'/'b'/; print TXT $str; 

Answer 1

Your program opens a file for append , so you won't be able to read from it and the line my $str = <TXT> will set $str to undef .

You can write this as a one-line console command, using

perl -i.backup -pe"s/'a'/'b'/g" myfile

which substitutes the string 'a' (including the quotes) with the string 'b' throughout the file, and saves a backup to myfile.backup

Or you can write a program like this

use strict;
use warnings;

open my $fh, '<', 'myfile' or die qq{Unable to open input file: $!};

while (<$fh>) {
  s/'a'/'b'/g;
  print $_;
}

which leaves the input file intact and sends the modified data to STDOUT, so it can be redirected to a new file with the command

perl modify.pl myfile > myfile.new

Answer 2

Look at this example:

 ...
open RH, "text.txt" or die $!;
chomp(my @lines = <RH>);
close RH;

open WH, ">text.txt" or die $!;
foreach my $line (@lines) {
  $line =~ s/'a'/'b'/;
  print WH "$line\n";
}
close WH;
 ...