Chapter 6

Now newcount.patch contains the following:

    Counter.pm.orig  Sat Jan 26 17:37:29 2002

+++ Counter.pm       Sat Jan 26 17:44:10 2002

@@  29,7 +29,10 @@

 # Preloaded methods go here.

 sub count { return scalar @_ }

+sub count {

+  my $pkg = shift;

+  return scalar @_;

+}

 1;

 __END__

This format is known as a unified diff. In a unified diff, lines that begin with a +

(plus sign) are the lines that have been added, and lines beginning with a   (minus 

sign) are the lines that have been removed. Lines without a leading character are 

context lines that are unchanged between old and new that surround the changes.

6

Including context enables patch to work even if the original files have changed 

since the patch was created. The additional context lines also help human readers 

understand the patch; with a little practice, you'll be able to read and understand 

patches as easily as reading the original source.

Unified diffs also contain a header listing the old and new filenames and their 

modification dates. As I'll demonstrate later, this allows changes to multiple files 

to be included in one patch.

Applying a Single File Patch

Applying patches is usually an easy process. The patch program accepts the patch 

file on standard input (known in Perl as STDIN). By default, it finds target files auto 

matically by examining the patch header and modifies them in place.

6. You can also get context in the normal diff format using the  c option, but unified patches are 

usually easier to read.

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