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==Basic Commands==
Commands that allow you to move around and create files within your file system can be found [[Quickstart/Linux Command Line| here]].

Alternatively if you were looking for File Permissions, these can be found [[FurtherTopics/Command Line File Permissions| here]].

==man== 
This will explain the use of man pages (also called manual pages) on Linux. Most Linux files and commands have pretty good man pages to explain their use.
Type man followed by a command (for which you want help) and start reading. Press q to quit the man page. See below:

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ man whois  (shows manual page for the command whois)
username@viper:~$ man syslog.config  (shows the manual page for a configuration file)
username@viper:~$ man syslogd (show the manual for a daemon (background program))
username@viper:~$ man –k syslog  (an apropos which shows a list of available man pages with this string contained within it)

</pre>

==Additional File Commands==
=== file ===

This command determines the file type. Unlike Windows, Linux does not determine the file type from the extension but from examining the file header/contents itself.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ file mypicture.png
pic33.png: PNG image data, 3840 x 1200, 8-bit/color RGBA, non-interlaced

username@viper:~$ file parallel.c
parallel.c: ASCII C program text

</pre>

=== head ===

By default, the head command will show the first ten lines of a file.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ head /etc/passwd

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/bin/sh
man:x:6:12:man:/var/cache/man:/bin/sh
lp:x:7:7:lp:/var/spool/lpd:/bin/sh
mail:x:8:8:mail:/var/mail:/bin/sh
news:x:9:9:news:/var/spool/news:/bin/sh

</pre>

=== tail ===

Similar to '''head''' but this time it will show the last 10 lines of the file by default.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ tail /etc/services
vboxd 20012/udp
binkp 24554/tcp 		# binkp fidonet protocol
asp 27374/tcp 		# Address Search Protocol
asp 27374/udp
csync2 30865/tcp 		# cluster synchronization tool
dircproxy 57000/tcp 	# Detachable IRC Proxy
tfido 60177/tcp 		# fidonet EMSI over telnet
fido 60179/tcp 		# fidonet EMSI over TCP

</pre>

=== tac ===

Works the same as '''cat''' but will show you the file backwards:

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ cat numbers
one
two
three

username@viper:~$ tac numbers
three
two
one

</pre>

=== more ===

The more command is useful for displaying files that take up more than one screen. More will allow you to see the contents of the file page by page. Use the space bar to see the next page, or q to quit. Some people prefer the less command to more.

=== less ===

Very similar to more but with some additional features

=== find ===

This command is very useful to find files, more options are provided on the command line by typing '''man find'''. Here are some useful examples below:

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ find /etc   (find all files in the /etc directory)
username@viper:~$ find . –name “*.conf”   (find all files that end in .conf from the current directory)
username@viper:~$ find . –newer file1.c   (find all files newer than file1.c)
username@viper:~$ find /etc >etcfiles.txt   (find all files but this time put them in (pipe) to the file etcfiles.txt)

</pre>

=== locate ===

The '''locate''' command is very different from find in that it uses an index to locate files. This is a lot faster than traversing all the directories, but it also means that it may be outdated too.

=== grep ===

The '''grep''' filter is famous among Linux (and UNIX) users. The most common use of '''grep''' is to filter lines of text containing (or not containing) a certain string.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ grep “Darren” /etc/passwd 
user:x:1000:1000:Darren Bird,,,:/home/user:/bin/bash

</pre>

As with most Linux commands, there are also a large number of useful options that will go with each command and '''grep''' is certainly no exception here

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ grep –i “Darren” /etc/passwd  (search in a case insensitive way)
username@viper:~$ grep –r “Darren” /etc/passwd  (search recursively down any directories too)
username@viper:~$ grep –v “Darren” /etc/passwd  (search for everything not containing “Darren”)

</pre>

=== wc ===

Counting words, lines, and characters are easy with '''wc'''.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ wc myfile.c  (show number of words, lines, and characters)
5 10 100 tennis.txt

</pre>

==Compression Commands==
=== gzip – gunzip ===

This is a useful compression program (like '''zip''' which also exists in Linux). The '''gzip''' command can make files take up less space.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ gzip myfile.c   (will create myfile.c.gz)
username@viper:~$ gunzip myfile.c.gz   (will create myfile.c again)

</pre>

=== bzip2 – bunzip2 ===

Files can also be compressed with '''bzip2''' which takes a little more time than '''gzip''', but compresses better.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ bzip2 myfile.c  (will create myfile.c.bz2)
username@viper:~$ bunzip2 myfile.c.bz2  (will create myfile.c again)

</pre>

=== zip – unzip ===

A compression program which is compatible with other '''zip''' programs found in MS Windows and other OSes.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ zip myfile.c   (will create myfile.c.zip)
username@viper:~$ unzip myfile.c.zip   (will create myfile.c again)

</pre>

==Other Commands==
=== date ===

The '''date''' command can display the date, time, time zone, and more.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ date
Sat Feb 23 12:44:30 BST 2017

</pre>

=== cal ===

The '''cal''' command displays the current month, with the current day highlighted.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ cal
     April 2016
Su Mo Tu We Th Fr Sa
                1  2
 3  4  5  6  7  8  9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30

</pre>


=== sleep ===

The '''sleep''' command is sometimes used in scripts to wait a number of seconds. This example shows a five-second sleep.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ sleep 5  (five seconds later)
username@viper:~$

</pre>

=== sort ===

The command '''sort''' will sort lines of text files. By default, the output is to the screen but this can be piped to a file or another program.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ sort myfile.txt
apple
banana
cherry

</pre>

=== time ===

The time command can display how long it takes to execute a command. The date command takes only a little time.

<pre style="background-color: black; color: white; border: 2px solid black; font-family: monospace, sans-serif;">

username@viper:~$ time date
Sat Feb 23 13:08:27 BST 2016
real 0m0.014s
user 0m0.008s
sys 0m0.006s

</pre>


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