Useful Linux Commands

Lists the free disk space of the system.
-h (human readable) provides a clear display of the sizes

Lists all subdirectories in the user's home directory and shows how much disk space each directory occupies.

File search: Searches for all TXT files in the user's home directory.

ls -l / | tee out.file | grep b

This example (from Wikipedia) filters the files and directories in the root directory for all those containing a b . At the same time, a file out.file is created with all files and directories in the root directory.

Displays a list of the currently running processes on the system (updated every 3 seconds by default).

Downloads a file from the internet.

Example script "myprint.sh":

#!/bin/bash
echo "Print on stdout." >&1
echo "Print on stderr." >&2

The example script "myprint.sh" generates output on the standard output (stdout) and the standard error output (stderr).

1. Redirect stdout (operator 1> or >):

$> myprint.sh 1> /dev/null

Print on stderr.

2. Redirect stderr (operator 2>):

$> myprint.sh 2> /dev/null

Print on stdout.

3. Redirect stdout and stderr (operator &>):

$> myprint.sh &> /dev/null

No output on the screen.

In the first example, the standard output is redirected to /dev/null (discarded) and only the standard error output remains on the screen.

In the second example it is the other way around: the standard error output is redirected and discarded, and only the standard output remains on the screen.

In the third example, both outputs are discarded.

Overview of file descriptors:

0 = Standard input (/dev/stdin)
1 = Standard output (/dev/stdout)
2 = Standard error output (/dev/stderr)
/dev/null - Null device (data stream is discarded)

Output forwarding and pipes:

1. stdout from scriptA to stdin of ScriptB:

$> ScriptA | ScriptB

2. stdout and stderr from ScriptA to stdin of ScriptB:

$> ScriptA 2>&1 | ScriptB

The | operator forwards the standard output of ScriptA to the standard input of ScriptB.

Note: the standard error output stderr is normally not forwarded! If stderr should also be forwarded, stderr must first be duplicated to stdout (see example 2).

Extracts a .tar.gz file.

Extracts a .tar.bz2 file.

Compresses all files in <myfolder> and creates the file <myfile.zip>.