Commands using perl

Find which directories on your system contain a lot of files.

Edit: much shorter and betterer with -n switch.

PmWiki stores wiki pages as Group.Name. Simply split the directory listing and count frequency of group occurances.

Perl version - just for completeness sake ;)

This version now adds a header with consecutive numbering.

Before running, do:

curl -sO http://world.std.com/%7Ereinhold/diceware.wordlist.asc

Lets say you have a file with the following layout:

LINUX,DIR,FILE1,FILE2,FILE3

You want the file to look like this:

LINUX,DIR,FILE1

LINUX,DIR,FILE2

LINUX,DIR,FILE3

This perl command does it for you.

I use this in my bashrc to expand hosts defined in ~/.ssh/config:

function _ssh_completion() {

perl -ne 'print "$1 " if /^Host (.+)$/' ~/.ssh/config

}

complete -W "$(_ssh_completion)" ssh

Here's a great article on how to setup your own ~/.ssh/config:

http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html

Find all files in /var/spool/mqueue older than 7 days, pass to perl to efficiently delete them (faster than xargs or -exec when you've got millions or hundreds of thousands to delete). Naturally the type, directory, and file age vars can be adjusted to meet your specific needs.

Can be run as a script `ftrace` if my_command is substrituted with "$@"

It is useful when running a command that fails and you have the feeling it is accessing a file you are not aware of.

If you've ever tried "grep -P" you know how terrible it is. Even the man page describes it as "highly experimental". This function will let you 'grep' pipes and files using Perl syntax for regular expressions.

The first argument is the pattern, e.g. '/foo/'. The second argument is a filename (optional).

this command example converts to 25 fps subtitles that were originally created for 24 fps movie

more idiomatic version of the same, using the flip-flop-operator; also printing lines with '//'-style comments

This is a naive way of finding source code comments in source code files that use C-like comments: // and /*...*/

Using tail to follow and standard perl to count and print the lps when lines are written to the logfile.

Recursively delete empty directories. Use with care.

Replace PACKAGE with desired package name.

Found here: http://mikebeach.org/2011/04/undo-apt-get-build-dep/

Can also just use the debug mode like this.

This is from perldoc -q random.*line, which says:

This has a significant advantage in space over reading the whole file in. You can find a proof of this method in The Art of Computer Programming, Volume 2, Section 3.4.2, by Donald E. Knuth.

Who am I to argue with Don Knuth?