Bash oneliners or helpful aliases for your .bashrc

Useful bash oneliners that might or might not be worth including as aliases in your ~/.bashrc file.

Bash Oneliners
command	action
grep -v "^#" $* | grep -v "^$"	print file contents excluding comments starting with # and empty lines
netstat -tpauln	print open TCP connections *and* application names
find . -maxdepth 1 -type d -exec du -sh {} \; | sort -hr	print sorted directory sizes starting with the biggest
find . -maxdepth 1 -mindepth 1 -type d -print0 | xargs -0 du -sh | sort -hr	same as above, but supposedly more efficient for lots of files
help test | less	does not do much work on itself but it is good reading
[ -n $SOMEVAR ] && echo "IS_NOT_EMPTY" || echo "IS_EMPTY"	execute first command on empty string, or execute second command otherwise (the Python way)
mkdir $(echo {01..22}spam)	create folders 01spam, 02spam, 03spam, etc.
cp filename{,.bak}	create backup of file
!!	rerun previous command
sudo !!	rerun previous command as root
python -m SimpleHTTPServer	run web server for current dir on port 8000 (Python 2.x version)
python -m http.server	run web server for current dir (Python 3 version)
:w !sudo tee %	write file in vim as root
ssh-copy-id remote-machine	copy rsa/dsa key to remote machine for public authentication
ffmpeg -f x11grab -s wxga -r 25 -i :0.0 -sameq /tmp/out.mpg	record current desktop to mpeg file
echo -e ${PATH//\:/\\n}	string replace with bash (the example replaces colon with end-of-line
curl -O http://rss.timegenie.com/forex.xml	download file to local file forex.xml
tr -dc ' -~' < /dev/urandom | head -c 20	generate random string
echo $(($RANDOM % 100))	generate random number in range
sudo find . -user root -exec chown spamneggs {} \;	find all files owned by root and change owner to spamneggs
function mcd { mkdir ${1} && cd ${1} }	a ~/.bashrc shortcut to make a directory and move into it.
function catw { cat `which "${1}"` }	a ~/.bashrc shortcut for typing cat `which script`
function vimw { vim `which "${1}"` }	a ~/.bashrc shortcut for typing vim `which script`; you get the idea...

See also:

• Top Ten One-Liners from CommandLineFu Explained
• 18 Useful bash scripts
• BashOneLiners

Running a command recursively on all files in a directory tree

Windows solution

Here is a script which calls mplayer on every file in a directory including subfolders:

The script will work on dirs containing spaces and non-ascii characters since all file names are converted to short dos names (via the `~s` modifier).

set mplayer=z:\path_to_mplayer\mplayer.exe
  for /f "delims=" %%f in ('dir /b /s "%cd%"') do (%mplayer% "%%~sf")

Linux bash solution

The bash shell solution is much easier to read than the windows one:

#!/bin/sh
cwd=`pwd`
for f in `find $cwd -type f -iname "*.mp3" `; do
    mplayer $f
done

A Better Solution

An alternative solution for both Windows and Linux would be to create a playlist file first, and then run a single mplayer instance with the -playlist switch:

Linux bash

#!/bin/sh
find $pwd -type f -iname "*.mp3" > /tmp/allfiles.m3u
mplayer -playlist /tmp/allfiles.m3u

Windows Batch

set mplayer=z:\path_to_mplayer\mplayer.exe
  set playlist=%TEMP%/mp3playlist.m3u
  dir /b /s "%cd%" | find /I ".mp3" > "%playlist%"
  %mplayer% -playlist "%playlist%"

Shortest solution

mplayer $(find . -iname "*.mp3")