Taking a screenshot in command-line is very easy using the import tool, which is included in the ImageMagick suite. To take a screenshot of a single window use:

import filename.png

To take a screenshot of a single window and include window decorations, use:

import -border filename.png

To take a screenshot of the entire screen or a region, type:

import filename.png

And then select with the mouse the region which you want to save.

To mount an ISO image, we’ll first create a mount point (an empty directory) and then we will use the mount command:

sudo mkdir /mnt/iso_image/
sudo mount -o loop iso_image.iso /mnt/iso_image/

pidof is a command which will return the PID of the process specified as argument. To kill an application we would use:

kill -9 $(pidof process_name)

For example:

kill -9 $(pidof amarokapp)
kill -9 $(pidof firefox-bin)

The first one kills Amarok, while the second one kills Firefox.

For this one we will use a tool called nrg2iso:

nrg2iso input_image.nrg output_image.iso

wc is a command-line tool which returns the number of lines, words or characters in a file, depending on which parameter we specify at the command-line. To count the number of lines:

wc -l input_file.txt

To count the number of words:

wc -w input_file.txt

And to count the total number of characters:

wc -c input_file.txt

For this one we’ll need conver, a tool which comes included with ImageMagick. convert allows to convert between various image formats, and apply tons of effects to images. Here’s an example on resizing an image:

convert -sample 30%x30% input_image.png output_image.png

Which will resize an image to 30% keeping its aspect ratio.

This is a way of converting Matroska Video files to AVI with mencoder:

mencoder input_file.mkv -ffourcc xvid -ovc lavc -lavcopts vcodec=xvid:vhq:vbitrate=1800 -oac mp3lame -lameopts vbr=5 -o output_file.avi

We will use genisoimage for this one. Here’s how to create an ISO 9660 image from a directory, keeping that directory as root:

genisoimage -o output_file.iso directory_name

And to create an image from several files, without including a root directory:

genisoimage -o output_file.iso file1 file2 file3

First, to see what ports are opened on your system use nmap:

nmap localhost

This will output a list of open ports and the protocol currently using them. To close any of them, use the following syntax as root:

fuser -k 80/tcp

Which will close port 80, the default port used by the web server.

For this one we will need the packages cuetools and shntool, which include the tools needed to split a big FLAC or WAV when a CUE file is available. Here’s the command:

cuebreakpoints cue_file.cue | shnsplit flac_file.flac

The same goes for WAV, just replace the .flac extension.

For APE files, we will first need to convert them to WAV using the mac tool, which comes in monkeys-audio package:

mac input_file.ape output_file.wav -d

And then split the WAV file just like it was showed above.

indent is a tool which allows to format and change the appearance of C code by inserting/deleting whitespace characters to make the code clearer and easier to read. Some of the coding styles it supports are GNU indent style (the default, also invoked with -gnu), Kernighan & Ritchie style (invoked with -kr) or Berkeley style (invoked with -orig). The example is as follows:

indent -kr source_file.c

Which will format source_file.c using the Kernighan & Ritchie style.

By default in Bash Ctrl+D will exit the current shell (unless used in a running application to mark end of file). To prevent this you can add the following line in ~/.bashrc:

export IGNOREEOF=1

And then source the file to read it again:

source ~/.bashrc

To temporarily disable the PC speaker you can remove its module from the kernel using the following command as root:

modprobe -r pcspkr

To permanently disable it, you can blacklist this module so it doesn’t load when the system starts. To do so, edit the /etc/modprobe.d/blacklist file as root and add the following line in it:

blacklist pcspkr

For this we will use mplayer like this:

mplayer input_file.vob -aid 128 -dumpaudio -dumpfile output_file.ac3

You can eventually concatenate VOB files first, e.g.:

cat VTS_01_1.VOB VTS_01_2.VOB VTS_01_3.VOB > ~/output_file.vob

And then proceed and use the mplayer on the newly create output_file.vob.

For this we will need the lm-sensors package. After installing it, you will have to load several kernel modules for temperature detection (this is done automatically and you only have to agree or disagree loading the specified module). To run it, just type sensors in a terminal:

$ sensors
coretemp-isa-0000
Adapter: ISA adapter
Core 0:      +46.0°C  (high = +74.0°C, crit = +100.0°C)

ffmpeg2theora is a frontend to ffmpeg which will allow us to convert various video files to the open format Theora video. Here’s an example:

ffmpeg2theora -q 6 -A 192 input_file.avi

This will convert input_file.avi to Theora video using a video quality factor of 6 and an audio bitrate of 192 kbps. Here’s another example, which will use the default settings:

ffmpeg2theora input_file.vob -o output_file.ogg

Or this one, which also adds meta tags to the video:

ffmpeg2theora --artist "Pink Floyd" --title "Live at Pompeii" input_file.vob -o output_file.ogg

We’ll use the ffmpeg audio and video encoder for this one:

ffmpeg -i input_file.ogv output_file.flv

To shrink the size of the resulting video use something like this:

ffmpeg -i input_file.ogv -s 640x512 output_file.ogv

To use a specific audio codec for audio output use the -acodec switch:

ffmpeg -i input_file.ogv -acodec libmp3lame output_file.flv

Aliases are a way of assigning a shorter, custom command to another single or a set of commands (or a one-liner and so on). To create aliases we can edit the ~/.bashrc file and add aliases like this:

alias 'killfx='kill -9 $(pidof firefox-bin)'
alias 'back=cd -' # or cd $OLDPWD
alias 'ls=ls -lhXa'

The first one will define a new custom alias, called killfx, which will kill Firefox when used. The second one will go back to the previous working directory, while the third one will make the ls to be aliased to ls -lhXa, which shows hidden files, detailed information, human readable sizes and sorts the files according to their type.

For this one we will use the iat utility:

iat input_file.nrg output_file.iso

iat can supports many image formats, including ISO, NRG, BIN and MDF.

For converting FLAC or WAV to Vorbis or MP3 we’ll need the vorbis-tools and lame packages. To convert from FLAC/WAV to Ogg Vorbis:

oggenc -b 256 input_file.flac -o output_file.ogg

Which will convert input_file.flac to Ogg Vorbis using a bitrate of 256 kbps. To convert FLAC to MP3 you will first need to convert it to WAV using flac -d input_file.flac and then convert the obtained WAV to MP3 using:

lame -b 192 input_file.wav

Which will use a bitrate of 192 kbps.

Have some more one-liners or tips? Please share them with us in the comments below!