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Compare copies of a file with md5

Find dead symbolic links
-L tells find to follow symbolic links, so -type l will only return links it can't follow (i.e., those that are broken).

Add directory to $PATH if it's not already there
Sometimes in a script you want to make sure that a directory is in the path, and add it in if it's not already there. In this example, $dir contains the new directory you want to add to the path if it's not already present. There are multiple ways to do this, but this one is a nice clean shell-internal approach. I based it on http://stackoverflow.com/a/1397020. You can also do it using tr to separate the path into lines and grep -x to look for exact matches, like this: $ if ! $(echo "$PATH" | tr ":" "\n" | grep -qx "$dir") ; then PATH=$PATH:$dir ; fi which I got from http://stackoverflow.com/a/5048977. Or replace the "echo | tr" part with a shell parameter expansion, like $ if ! $(echo "${PATH//:/$'\n'}" | grep -qx "$dir") ; then PATH=$PATH:$dir ; fi which I got from http://www.commandlinefu.com/commands/view/3209/. There are also other more regex-y ways to do it, but I find the ones listed here easiest to follow. Note some of this is specific to the bash shell.

Extract tar content without leading parent directory
If archive has leading directory level same as archive name and you want to strip it, this command is for you.

Recursive Line Count

Remove all HTML tags from a file
A shorter version of command #3014, using awk instead of sed. Useful when scraping websites with a script.

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Advanced python tracing
Trace python statement execution and syscalls invoked during that simultaneously

Check hashes of files installed by Debian packages, reporting only errors.

seq can produce the same thing as Perl's ... operator.
Optionally, one can use {1..50} instead of seq. E.g. for i in {1..50} ; do echo Iteration $i ; done


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