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commandlinefu.com 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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Super Speedy Hexadecimal or Octal Calculations and Conversions to Decimal.
^Hexadecimal Ten minus Octal Ten is Eight(in Decimal). $ echo "$(( 0xaf )) = $(( 0257 ))" ^Hexadecimal AF and Octal 257 are both Decimal 175.

Display a wave pattern
Purely frivolous - print a sine/cosine curve to the console - the width varies as it progresses. Ctrl-C to halt.

check open ports without netstat or lsof

Insert the last argument of the previous command
for example if you did a: $ ls -la /bin/ls then $ ls !$ is equivalent to doing a $ ls /bin/ls

Run a command when a file is changed

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"

recursive search and replace old with new string, inside files
recursively traverse the directory structure from . down, look for string "oldstring" in all files, and replace it with "newstring", wherever found also: $ grep -rl oldstring . |xargs perl -pi~ -e 's/oldstring/newstring'

Parse m3u playlist file for total time
Parse an m3u file with seconds for each item and output the length of the entire playlist

Calculate days on which Friday the 13th occurs (inspired from the work of the user justsomeguy)
Friday is the 5th day of the week, monday is the 1st. Output may be affected by locale.

Find public IP when behind a random router (also see description)
Depends on GET. You can also replace GET with curl, or `wget -qO -` if GET isn't available.


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