Replacing text in a file using perl script

[Patricia Samuel]

Hi All,

I need to replace some value in config file using perl script. I used this code -

open (IN, "default.properties");

@file = <IN>;

seek IN,0,0;

foreach $file (@file){
$file =~ s/ftp='pass'/ftp='pass1'/g;
print IN $file;
}
close IN;

  

When i print $file , it shows me the changed rows but it does not write it to a file. Please suggest.

Regards,
Patricia samuel

[James Sabre]

Since your are reading the whole file into memory you can safely re-open the file and write to it i.e.

#!/usr/bin/perl
$file = "default.properties";
open (IN, $file) || die "Cannot open file ".$file." for read";     
@lines=<IN>;  
close IN;

open (OUT, ">", $file) || die "Cannot open file ".$file." for write";
foreach $line (@lines)
{  
   $line =~ s/hello/hello hello hello/ig;  
   print OUT $line;  
}  
close OUT;  

[Colin Wray]

I just learnt, much to my surprise, that the following code works too:

foreach $line (@lines)
{  
   $line =~ s/hello/hello hello hello/ig;  
}
print OUT @lines;
close OUT;

I had no idea that changing $line in the for loop actually changed the @lines array.

[fred rosenberger]

James Sabre wrote:Since your are reading the whole file into memory you can safely re-open the file and write to it i.e.

I would NEVER write the changed lines out to the same file.  Odds are too great that you screw something up, and your original file is lost forever.  I'd always write the output to a new temp file, inspect it to be sure it is correct, and then rename the original as a .old or some such.

[Tim Holloway]

Perl has a command-line option for this. It makes the change "in place", but also produces a back-up copy of the original file.

This is invaluable, since I almost never get the changes right on the first try!