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Re^3: very new to perl; suggestions for porting this shell script to perl?

by Cristoforo (Deacon)
on May 29, 2011 at 20:35 UTC ( #907240=note: print w/ replies, xml ) Need Help??


in reply to Re^2: very new to perl; suggestions for porting this shell script to perl?
in thread very new to perl; suggestions for porting this shell script to perl?

Yes, the sample files and output clarified the problem.

Here is a solution, but you should probably check it to see if it meets your specifications.

#!/usr/bin/perl use strict; use warnings; my @files = glob "/usr/share/applications/*.desktop"; my $regex = join "|", qw/ Audio Graphics Network Settings System Utili +ty /; my %data; FILE: for my $file (@files) { open my $fh, "<", $file or die "Unable to open $file (for reading) +. $!"; my ($category, $name, $exec); while (<$fh>) { if(/^Categories=.*?\b($regex)\b/) { $category ||= $1; # sets cat for first time only (each fil +e) } elsif (/^Name=(.+)$/) { $name ||= $1; # sets name first time only (each file) } elsif (/^Exec=(\S+)/) { $exec ||= $1; # sets exec first time only (each file) } } close $fh or die "Unable to close $file. $!"; for ($category, $name, $exec) { if (! defined) { warn "$file missing category or name or exec.\n"; # skip the 'push' below and go to the label 'FILE:' next FILE; } } push @{ $data{ $category } }, {name => $name, exec => $exec}; } for my $category (keys %data) { print "Submenu = \"$category\" {\n"; my @recs = @{ $data{ $category } }; for my $href ( @recs ) { # hash reference print " Entry = \"$href->{name}\" { Actions = \"$href->{ex +ec}\" }\n"; } print "}\n"; }

Notice how all the variables are declared with my. Declaring variables this way helps catch spelling errors and also limits the scope to the innermost containing block. This property is handy and can be seen in the declaration of my ($category, $name, $exec)

Every time the for loop starts a new iteration, (with a new file), it gets a fresh copy of 'undefined' variables. Then, later on they are assigned to, ($category ||= $1;). The first time a valid match is made, an assignment will happen. If there are more than 1 instance of name or exec (as you noted in your post), they will be ignored. This is because any of the three already has the first match assigned to it.

The data is stored in the %data hash (which is then printed out when the loop terminates).

The glob function does wildcard expansion and returns all the matching files. (gimp.desktop and all other files with the .desktop extension).

There are many other Perl idioms here and if you have questions about just why a certain piece is written the way it is, just ask.

If you plan on using Perl now on, it would be probably helpful to read a book such as Learning Perl witch is a good intro to Perl or Programming Perl which is larger but a good reference book.


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Re^4: very new to perl; suggestions for porting this shell script to perl?
by Anonymous Monk on May 30, 2011 at 23:53 UTC

    It's working great! I've only made a few changes. I changed the (/^Exec=(\S+)/) back to (/^Exec=(.*)/) because I still want to preserve the flags present at the end of some "Exec=xxx" lines (for example: "Exec=pcmanfm-mod --find-files" which corresponds to a "Name=Search for Files and Folders"), while still excluding %f, %F, %u and %U from any entries, because these act as placeholders for the filenames or urls on which the user has right-clicked.

    The new script did create a small issue, however. I noticed that it prints the submenus in a different order from how they're listed. Do you know of any simple ways to make it respect the order in which they're specified when they're assigned at "my $regex ="? If not, it's completely usable how it is and I'll keep it in mind as I'm reading some of the books you suggested.

      Oops.. That last comment was mine. I had forgotten to login.
      I'm glad to hear it works OK. :-)
      You never really know until you run it against some data I guess.

      Do you know of any simple ways to make it respect the order in which they're specified when they're assigned at "my $regex ="?
      That occured to me after I posted the code, but I wasn't sure it was necessary.

      Since your categories list is in alphabetical order, you could sort the keys in the print routine like:

      for my $category (sort keys %data).

      Glad to be of help!

      Update: Just for the record, if the order of records was not in sort order, a few small changes would handle that situation.

      At the top of the script, before the for loop, you would enter:

      my @cat = qw/ Audio Graphics Network Settings System Utility /; # in y +our desired order my $regex = join "|", @cat; my @files = glob "/usr/share/applications/*.desktop"; # as before

      Then a small change to the print routine:

      for my $category ( @cat ) { next unless exists $data{ $category }; print "Submenu = \"$category\" {\n"; . . . . .

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