Can a Perl script modify itself?

Question

I would like to have my scripts keep track of thier last date of revision internally as a comment. Is this possible? It seems to me that it would need to grab the date and

Answer 1

You can get your version control system to do this automatically.

But if you are using version control then this step is really not nesaccery in the first place.

Answer 2

Sounds like you already know how to do it. If it is a perl script on a unix/linux box then permissions should not be an issue, if it is on a windows box it might not let you as the file is in use

-- John

Answer 3

#! /usr/bin/env perl
use warnings;
use strict;
use autodie;

{
  open my $self, '>>', $0;
  my $time = localtime;
  print {$self} "# ran on $time\n";
}

__END__
# ran on Wed Aug 25 16:41:05 2010

Answer 4

It is possible, but that doesn't make it a good idea. For one thing, it wouldn't update the date until you ran it.

If you're using a good editor, it may have a way to insert a timestamp automatically when you save the file. For example, I set up Emacs to do that in HTML files using write-contents-hooks. (It would need some modification to work with Perl code, but cjm-html-timestamp in cjm-misc.el would give you a starting point.)

Answer 5

By request adding my comment as an answer.

Sounds like you already know how to do it. If it is a perl script on a unix/linux box then permissions should not be an issue, if it is on a windows box it might not let you as the file is in use.

Answer 6

The following worked on a FreeBSD system. It appends to the end, which sounds acceptable to you, but doesn't conform to the "normal" way of documenting changes within a file - at least for me, as I've almost always seen it done at the beginning. You'll probably want to change the way the date/time is displayed.

#!/usr/bin/perl -w
open SELF, ">> selfModify.pl" or die "Unable to open self";
print SELF "# ran/modified at " . join(' ', localtime()) . "\n";
close(SELF);

Whether this is wise or not I'll leave for you to decide.