set of useful commands

tips.linux.sh

# turn off the given monitor
xrandr --output LVDS --off

# enable/disable composting
xfconf-query --channel=xfwm4 --property=/general/use_compositing --type=bool --toggle

# exit the script if try to use an uninitialized variable
set -u

# exit the script if any statement returns a non-true return value
set -e

# SSH socks proxy
ssh -D 5555 user@remotehost -f -N

# map the remote port 3306 to local 33060
ssh -L 33060:127.0.0.1:3306 user@remotehost

# file creation of the given size
dd if=/dev/zero of=file.dat count=1 bs=1M
truncate -s 10G file.dat
fallocate -l 5T file.dat

# iterating files
for f in file1 file2 file3; do echo "processing $f"; done
for f in *.txt; do echo "processing $f"; done

# processing file line by line with separation
while read part1 part2 part3; do
	echo "$part3 :: $part1"
done < data.txt

# find & replace across multiple files
find . -type f -name "*.txt" -print0 | xargs --null sed -i "s/foo/bar/g"
find . -type f -name "*.txt" -exec sed -i 's/foo/bar/g' "{}" \;  # many sed processes
find . -type f -name "*.txt" -exec sed -i 's/foo/bar/g' "{}" +;  # single sed process

# files and dirs recursive permissions correction
find /some/path/ -type f -exec chmod 644 "{}" \;
find /some/path/ -type d -exec chmod 755 "{}" \;

# change files ownership in a directory recursively from a user to another
chown -cR --from=olduser:oldgroup newuser:newgroup ./*
find . -user olduser -exec chown newuser:newgroup "{}" \;
find . -uid 1024 -exec chown newuser:newgroup "{}" \;

# remove files recursively
find -name "smth.*" | xargs rm;
find -name "smth.*" -exec rm {} \;
find -name "smth.*" -delete;
rm -rvf smth.*
rm -- smth*

# remove all duplicates in the current directory
fdupes --recurse --delete --noprompt .

# delete all empty folders in current directory
find . -type d -empty -delete

# file lines count
wc -l some.txt
sed -ne '$=' some.txt
grep -c "" some.txt

# get media file meta-data
mplayer -vo null -ao null -identify -frames 0 -v somefile.mkv

# play video with two audio tracks simultaneous output to different sound cards
mplayer -udp-slave -aid 0 -vo null -ao alsa:device=hw=1.0 somefile.mkv
mplayer -udp-master -aid 1 somefile.mkv

# extract audio track from video file
avconv -i media.avi -acodec copy -y media.mp3