FurtherTopics/Linux Command Line Advanced
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Contents
Basic Commands
Commands that allow you to move around and create files within your file system can be found here.
Alternatively if you were looking for File Permissions, these can be found 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:
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)
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.
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
head
By default, the head command will show the first ten lines of a file.
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
tail
Similar to head but this time it will show the last 10 lines of the file by default.
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
tac
Works the same as cat but will show you the file backwards:
username@viper:~$ cat numbers one two three username@viper:~$ tac numbers three two one
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:
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)
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.
username@viper:~$ grep “Darren” /etc/passwd user:x:1000:1000:Darren Bird,,,:/home/user:/bin/bash
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
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”)
wc
Counting words, lines, and characters are easy with wc.
username@viper:~$ wc myfile.c (show number of words, lines, and characters) 5 10 100 tennis.txt
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.
username@viper:~$ gzip myfile.c (will create myfile.c.gz) username@viper:~$ gunzip myfile.c.gz (will create myfile.c again)
bzip2 – bunzip2
Files can also be compressed with bzip2 which takes a little more time than gzip, but compresses better.
username@viper:~$ bzip2 myfile.c (will create myfile.c.bz2) username@viper:~$ bunzip2 myfile.c.bz2 (will create myfile.c again)
zip – unzip
A compression program which is compatible with other zip programs found in MS Windows and other OSes.
username@viper:~$ zip myfile.c (will create myfile.c.zip) username@viper:~$ unzip myfile.c.zip (will create myfile.c again)
Other Commands
date
The date command can display the date, time, time zone, and more.
username@viper:~$ date Sat Feb 23 12:44:30 BST 2017
cal
The cal command displays the current month, with the current day highlighted.
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
sleep
The sleep command is sometimes used in scripts to wait a number of seconds. This example shows a five-second sleep.
username@viper:~$ sleep 5 (five seconds later) username@viper:~$
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.
username@viper:~$ sort myfile.txt apple banana cherry
time
The time command can display how long it takes to execute a command. The date command takes only a little time.
username@viper:~$ time date Sat Feb 23 13:08:27 BST 2016 real 0m0.014s user 0m0.008s sys 0m0.006s