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count the number of specific characters in a file or text stream
In this example, the command will recursively find files (-type f) under /some/path, where the path ends in .mp3, case insensitive (-iregex). It will then output a single line of output (-print0), with results terminated by a the null character (octal 000). Suitable for piping to xargs -0. This type of output avoids issues with garbage in paths, like unclosed quotes. The tr command then strips away everything but the null chars, finally piping to wc -c, to get a character count. I have found this very useful, to verify one is getting the right number of before you actually process the results through xargs or similar. Yes, one can issue the find without the -print0 and use wc -l, however if you want to be 1000% sure your find command is giving you the expected number of results, this is a simple way to check. The approach can be made in to a function and then included in .bashrc or similar. e.g. $ count_chars() { tr -d -c "$1" | wc -c; } In this form it provides a versatile character counter of text streams :)

Write comments to your history.
A null operation with the name 'comment', allowing comments to be written to HISTFILE. Prepending '#' to a command will *not* write the command to the history file, although it will be available for the current session, thus '#' is not useful for keeping track of comments past the current session.

Prettify an XML file
Like `tidy`, `xmllint` can be used to prettify XML files. The --nsclean option is also useful to remove redundant namespaces.

Merge various PDF files

Clear filesystem memory cache
Found here: http://ubuntuforums.org/showthread.php?t=589975

list block devices
Shows all block devices in a tree with descruptions of what they are.

look for a function reference in a library set

list all opened ports on host

Locking and unlocking files and mailboxes
Programs for locking and unlocking files and mailboxes.This package includes several programs to safely lock and unlock files and mailboxes from the command line. These include: lockfile-create lockfile-remove lockfile-touchlock mail-lock mail-unlock mail-touchlock These programs use liblockfile to perform the file locking and unlocking, so they are guaranteed compatible with Debian's file locking policies.

list files recursively by size


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