The situation to use the one liner (Re: APM: One liner to get hash from an environment list)

[Bill Raty]

Fellow Mongers (and Sam),

This note isn't written to say the one-liner is superior to the
other fine means from CPAN, but rather to describe the one
situation which best exhibits its strength.  Read on if you're
interested.

Yes you can combine the regexes (or transform them, or use
grep) to filter out comments if such is your which.  How is
left as an excercise of the class.  Hint: Schwarzian transform.

However this brings us full circle to why the one liner was
written in the first place.  The original code that the one
liner replaced was written to parse a shell script provided by
a third party that set-up a database environment that had to be
available from processes executed from Perl.  When the DB
engine was updated by the third party, the updated shell script
broke the rather simple parsing rules of the perl code used,
although the shell script remained perfectly legal.  

The one liner replaced about of score of lines of logic and
relied upon the fact that a shell best knows how to interpret
shell commands, and made the Perl script immune from changes to
the third-party maintained script.

The original one liner:

%ENV = map /(^.*?)=(.*)/, qx( /some/script; env );

Will work for any version of /some/script that is valid for its
shell interpreter, without reduplication of shell logic in
Perl.  This holds with standard Unix philosophy: stand on the
shoulders of giants.

The same holds for the CPAN modules (of which there are dozens
of configuration schemes from Winduhs style .ini files to XML).
 If you're trying to leverage a shell script provided by a
third party (DB vendor) that is written for a particular shell,
its probably best to have the referenced shell interpret said
script.

My $0.02,

-Bill

--- Sam Foster <austin.pm at sam-i-am.com> wrote:
> > %config = map { /(.*?)=['"]?(.*)['"]?/ } qx(cat
> /etc/defaults/some_prog_env.sh);
> > 
> > This should parse any valid bourne shell syntax key=value
> config file
> > into a hash.
> 
> but if you want to allow #comments, blank lines etc, you
> might end up 
> with something like this?
> 
> my %config;
> foreach ( qx(cat /your/input/file) ) {
> 	next if /^\s*#/;	# skip commented lines
> 
> 	# match for name=value pairs, allowing for indentation and
> 	# options whitespace around the '='.
> 	# We should really use a backreference to pair up the
> quotes?
> 	next unless ( /\s*(.*?)\s*=\s*['"]?(.*)['"]?/ );
> 	$config{$1} = $2;
> }
> 
> Can you combine the regexps to get this back on one line?
> (for those 
> who take joy from this sort of thing?)
> 
> Sam
> 
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