Commands by Haegin (3)

What's this? is the place to record those command-line gems that you return to again and again. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.

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Find status of all symlinks
The symlinks command can show status of all symbolic links, including which links are dangling, which symlinks point to files on other file systems, which symlinks use ../ more than necessary, which symlinks are messy (e.g. having too many slashes or dots), etc. Other useful things it can do include removing all dangling links (-d) and converting absolute links to relative links (-c). The path given must be an absolute path (which is why I used $(pwd) in the example command).

dd if=/dev/null of=/dev/sda
removes all files/filesystems of a harddisk. It removes EVERYTHING of your hard disk. Be carefull when to select a device. It does not prompt for and second check.

tar and remove files which are older that 100 days
tar does not have a -mtime option as find. tar appends all the file to an existing tar file.

Send test prints to networked printer.
This will send a test print job to a networked printer.

draw mesh

Using awk to sum/count a column of numbers.
Takes a input file (count.txt) that looks like: 1 2 3 4 5 It will add/sum the first column of numbers.

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"

Remove duplicate rows of an un-sorted file based on a single column
The command (above) will remove any duplicate rows based on the FIRST column of data in an un-sorted file. The '$1' represents a positional parameter. You can change both instances of '$1' in the command to remove duplicates based on a different column, for instance, the third: $ awk '{ if ($3 in stored_lines) x=1; else print; stored_lines[$3]=1 }' infile.txt > outfile.txt Or you can change it to '$0' to base the removal on the whole row: $ awk '{ if ($0 in stored_lines) x=1; else print; stored_lines[$0]=1 }' infile.txt > outfile.txt ** Note: I wouldn't use this on a MASSIVE file, unless you're RAM-rich ;) **

Create a 5 MB blank file via a seek hole
Similar to the original, but is much faster since it only needs to write the last byte as zero. A diff on testfile and will return that they are the same.

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Follow the Tweets.

Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.


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