Linux commands

I'm starting a list of useful linux shell commands (generally "one liners") we use a lot

Image Manipulation

Resizing JPG's and changing quality setting

The first line shows how to reduce and image to 25% and quality to 50% adding "_resized" to the results filename. The second command uses Perl to apply this same command to all JPG's in the current directory.

{{{1}}}

Apply an opaque background of a specified colour to a directory of transparent PNG's

• This command requires ImageMagick to be installed
• It loops through all PNG's in the CWD and puts them in a directory called processed which must exist

<bash> perl -e 'qx "convert $_ -background #ff00ff -flatten foo/$_" for glob "*.png"' </bash>

See also

• Converting_microarray_images for bash/imagemagick image file manipulation

Files

Get the size of a directory and its contents

<bash> du -sh /home/foo </bash>

Search and replace content in files

You could also use find and sed, but I find that this little line of perl works nicely.

<bash> perl -pi -w -e 's/SEARCH/REPLACE/g;' *.php </bash>

• -e means execute the following line of code.
• -i means edit in-place
• -w write warnings
• -p loop

EXTS="7z t7z"

Network commands

Release DHCP lease

<bash> sudo dhclient -r </bash>

Obtain a new DHCP lease

<bash> sudo dhclient </bash>

Devices

mount

All files accessible in a Unix system are arranged in one big tree, the file hierarchy, rooted at /. These files can be spread out over several devices. The mount command serves to attach the file system found on some device to the big file tree.

<bash> mount [/dev/device] [/media/directory] </bash>

fstab

Static information about the filesystems (fstab) is a configuration file that contains information of all the partitions and storage devices in your computer. It is a map of devices to the point in the filesytem where the device can be accessed, it contains information of where your partitions and storage devices should be mounted and how. It acts as a set of defaults for devices that are specified using the mount command where the file system directory is not specified. See W:Fstab#Example.

<bash> cat /etc/fstab </bash>

Mount a .iso

See this HOWTO

See also

• Linux commands cheatsheet