Module Maintenance

chapters. I'll change the count() routine in Counter.pm to work as a class method 

rather than as a simple function. First, I copy Counter.pm to Counter.pm.orig:

$ cp Counter.pm Counter.pm.orig

Next I edit Counter.pm, changing the definition of count() from

sub count { return scalar @_ }

to this:

sub count {

  my $pkg = shift;

  return scalar @_;

}

Now I can produce a patch file by running the diff command on the files and 

redirecting the output to a file called newcount.patch. The order of the arguments is 

important always put the old file first and then the new file:

diff Counter.pm.orig Counter.pm > newcount.patch

The diff program describes the differences in terms of what parts of the file would 

have to change to get from one version to a different version. Since you want to be 

able to see how to get from the original version to the new version, the original 

version goes first. Reversing the filenames would tell you exactly how to get from 

the new version back to the old version.

After this command, newcount.patch contains the following:

32c32,35

< sub count { return scalar @_ }

> sub count {

>   my $pkg = shift;

>   return scalar @_;

> }

Lines that begin with < are the lines that have been removed from the old file, and 

the lines beginning with > are the lines that have been added in the new file.

The diff program can represent differences between files in a number of dif 

ferent formats. The patch program can be used with the diff format shown previously, 

but it's not the preferred format. To produce a better patch, use the  u option:

diff  u Counter.pm.orig Counter.pm > newcount.patch

14

145

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