Abigail

my $fil = 'file.txt';
open(DATA, "$fil") || die "Can not open: $!\n";
my @dat = (<DATA>);
close(DATA);
open(DATA, ">$fil") || die "cant write: $!\n";

                                     
foreach (@dat)
{
    if($_ =~ /number/)
    {
        s/number/NEWWORD/;
        print DATA $_;
    }
}
close(DATA);
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You need to print out all the other lines also.

If you want to edit a line and leave it in the file then just get rid of the if.

...
foreach (@dat)
{
  s/number/NEWWORD/;
  print DATA $_;
}
close(DATA);
[download]

This will change the lines that need changing and print everything into the file.

There is another risk with this method that if the program dies before getting the file printed back out your original file which was erased on the second open will not have the complete data. This is what the backup options cover you against.

This will do the translation and leaves a backup file in this case named file.txt.bak.

perl -pi.bak -e 's/number/NEWWORD/;' file.txt
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The -p says to print every line, the -i.bak says make a backup file by adding .bak to the input file name, -e says to run the next argument as a perl script. The substitute only happens if the pattern matched so there is no need for an if unless you want to locate one pattern and then replace another pattern with yet a different replacement.

Here's another way, using grep to exclude lines matching the unwanted pattern as they are read in from the file:

...
use strict;

my $file = 'data_file.txt';
my $bad_pattern = '019';

open my $in_fh, "<$file" or die "can't open $file to read";
my @good_lines = grep { !/$bad_pattern/ } <$in_fh>;
close $in_fh;

open my $out_fh, ">$file" or die "can't open $file to write";
print $out_fh $_ foreach @good_lines;
close $out_fh;
[download]

thanks it now works with what you gave me:

foreach (@dat)
  {
    s/number/NEWWORD/;
    print DATA $_;
  }
  close(DATA);
[download]

Not sure I can use the perl command line backup example you gave me:

  perl -pi.bak -e 's/number/NEWWORD/;' file.txt
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because this is in a cgi web page script. Can I do some backup work as you suggested with this?

foreach (@dat)
  {
    s/number/NEWWORD/;
    print DATA $_;
  }
  close(DATA);
[download]

...you cannot just edit a file in place...

This has been coming up a lot recently. See Tie::File:

"Tie::File" represents a regular text file as a Perl array. Each element in the array corresponds to a record in the file. The first line of the file is element 0 of the array; the second line is element 1, and so on. The file is not loaded into memory, so this will work even for gigantic files. Changes to the array are reflected in the file immediately.

For an example of changing a file in place using Tie::File, see this node and this node.