Update: Sigh. Seeing your reply to RollyGuy, maybe all you want is to backwhack the slash or backslash like so:

perl -pi -e's/\{\/rtf1\}//g' /path/to/file.ini

</Update>

The basic method for that is to read the old file, make your modifications, then write the result to a either a new file or over the old one, and finally rename the new file, if used, over the old. There are several reasons to take all those steps.

• You must not clobber the old file with an ordinary open to write, since you need to read it.
• More than one instance of your application may be running, so you need to protect against interference between them.

The interference can happen several ways. A newly started instance may read its configuration from a half-written file. An instance may try to rewrite the configuration and find an empty file for a basis, if another instance is doing the same. These conditions are called races.

Whether you write to a copy and rename depends on whether you read the whole file into memory, or edit as a stream. Both techniques demand care with file locking.

Here is a single file technique:

use Fcntl qw( :flock );
{
    my $ini;
    open $ini, '+<', "$path/$fname" or die $!;
    flock $ini, LOCK_EX;
    my @lines = <$ini>;
    seek $ini, 0, 0;
    print $ini edit(@lines) or die $!;
    close $ini or die $!;
}
[download]

I've assumed some sub edit is defined which returns a list of lines for the new file.

In some circumstances it may be useful to use sysopen since it permits file modes that are unavailable with open. For a stream edit, this technique is like the edit mode '-pi=bak' available from the command line:

use Fcntl;
{
    my {$in,$out);
    sysopen $out, "$path/$fname.bak",
              O_WRONLY | O_CREAT | O_EXCL | O_EXLOCK
        or sleep 1 and redo;
    open $in, '<', "$path/$fname" or die $!;
    flock $in, LOCK_EX;
    while (<$in>) {
        # edit operations to modify or skip $_
        print $out or die $!;
    }
    close $in;
    close $out or die $!
    rename "$path/$fname.bak", "$path/$fname" or die $!;
}
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Here, output file locking is done with the combination of flags in sysopen. The use of O_EXCL with rename is worth study.

I've used some Perl 5.6 -isms with lexical handles and 3-arg open, but all this can be done with global handles and two arg open, as well.

After Compline,
Zaxo