Difference between revisions of "Core utilities"

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[[Category:Command shells]]
 
[[Category:Command shells]]
 
[[it:Core Utilities]]
 
[[it:Core Utilities]]
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[[ja:Core Utilities]]
 
[[zh-CN:Core Utilities]]
 
[[zh-CN:Core Utilities]]
{{Article summary start}}
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{{Related articles start}}
{{Article summary text|Tips and tricks related to so-called "core" utilities on a GNU/Linux system.}}
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{{Related|Bash}}
{{Article summary heading|Related}}
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{{Related|Zsh}}
{{Article summary wiki|Commandline Tools}}
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{{Related|General Recommendations}}
{{Article summary wiki|Bash}}: improved Bourne shell, Linux standard
+
{{Related|GNU Project}}
{{Article summary wiki|Zsh}}: improved Bourne/C shell, very good as interactive shell
+
{{Related articles end}}
{{Article summary wiki|General Recommendations}}
+
This article deals with so-called ''core'' utilities on a GNU/Linux system, such as ''less'', ''ls'', and ''grep''. The scope of this article includes, but is not limited to, those utilities included with the GNU {{Pkg|coreutils}} package. What follows are various tips and tricks and other helpful information related to these utilities.
{{Article summary wiki|GNU Project}}
+
{{Article summary end}}
+
 
+
This article deals with so-called "core" utilities on a GNU/Linux system, such as '''less''', '''ls''', and '''grep'''. The scope of this article includes - ''but is not limited to'' - those utilities included with the GNU {{Pkg|coreutils}} package. What follows are various tips and tricks and other helpful information related to these utilities. If sections grow too detailed, please split into separate articles.
+
  
 
== cat ==
 
== cat ==
Line 19: Line 16:
 
[[Wikipedia:cat_(Unix)|cat]] (''catenate'') is a standard Unix utility that concatenates and lists files.
 
[[Wikipedia:cat_(Unix)|cat]] (''catenate'') is a standard Unix utility that concatenates and lists files.
  
* As '''cat''' is not a shell built-in, in many occasions you may find more convenient to use a redirection, for example in scripts, or if you care a lot about performance. In fact {{ic|$ < ''file''}} does the same of {{ic|$ cat ''file''}}.
+
* As ''cat'' is not a shell built-in, on many occasions you may find more convenient to use a [[wikipedia:Redirection (computing)|redirection]], for example in scripts, or if you care a lot about performance. In fact {{ic|< ''file''}} does the same of {{ic|cat ''file''}}.
  
 
* To append multiple lines to a file a construct like this one is used:
 
* To append multiple lines to a file a construct like this one is used:
  
  cat << EOF >> ''path/file''
+
{{bc|
''first line''
+
$ cat << EOF >> ''path/file''
...
+
''first line''
''last line''
+
...
EOF
+
''last line''
 +
EOF
 +
}}
 +
 
 +
* If you need to list file lines in reverse order, there is a utility called [[Wikipedia:tac (Unix)|tac]] (''cat'' reversed).
 +
 
 +
== cron ==
 +
 
 +
[[Wikipedia:cron|cron]] is a time-based job scheduler in Unix-like computer operating systems.
  
* If you need to cat file lines in reverse order, there is a utility called '''tac''' (''cat'' reversed).
+
See the [[cron|main article]].
 +
{{Note|''systemd'' is able to handle many ''cron'' use cases. See the [[systemd/cron_functionality|related article]].}}
  
 
== grep ==
 
== grep ==
  
[[Wikipedia:grep|grep]] (''global regular expression print'') is a command line text search utility originally written for Unix. The '''grep''' command searches files or standard input globally for lines matching a given regular expression, and prints them to the program's standard output.  
+
[[Wikipedia:grep|grep]] (from [[Wikipedia:ed|ed]]'s ''g/re/p'', ''global/regular expression/print'') is a command line text search utility originally written for Unix. The ''grep'' command searches files or standard input globally for lines matching a given regular expression, and prints them to the program's standard output.
* Remember that grep handles files, so a construct like {{ic|<nowiki>$ cat ''file'' | grep ''pattern''</nowiki>}} is replaceable with{{ic|$ grep ''pattern'' ''file''}}
+
  
* If you have to grep VCS source code, there is an optimized utility written in Perl and called {{Pkg|ack}}. See the [http://beyondgrep.com/ official web site].
+
* Remember that ''grep'' handles files, so a construct like {{ic|cat ''file'' <nowiki>|</nowiki> grep ''pattern''}} is replaceable with {{ic|grep ''pattern'' ''file''}}
  
== Color ==
+
* If you have to grep VCS source code, there is an optimized utility written in Perl and called {{Pkg|ack}}. See the [http://beyondgrep.com/ official web site].
  
Beyond aesthetics, '''grep'''&#39;s color output is immensely useful for learning [[Wikipedia:regexp|regexp]] and '''grep'''&#39;s functionality.
+
=== Colored output ===
  
To use the default colors for '''grep''', write the following entry to your shell configuration file, e.g. if using [[Bash]]:
+
Beyond aesthetics, ''grep''&#39;s color output is immensely useful for learning [[Wikipedia:regexp|regexp]] and ''grep''&#39;s functionality.
 +
 
 +
To use the default colors for ''grep'', write the following entry to your shell configuration file, e.g. if using [[Bash]]:
 
{{hc|~/.bashrc|2=alias grep='grep --color=auto'}}
 
{{hc|~/.bashrc|2=alias grep='grep --color=auto'}}
Alternatively, you can set the '''GREP_OPTIONS''' [[Environment Variables|environment variable]] [http://www.gnu.org/software/grep/manual/html_node/Environment-Variables.html] bearing in mind this may break some scripts that use '''grep''' [http://brainstorm.ubuntu.com/idea/24141/]:  
+
Alternatively, you can set the {{ic|GREP_OPTIONS}} [[Environment Variables|environment variable]] bearing in mind this may break some scripts that use ''grep'' [http://brainstorm.ubuntu.com/idea/24141/]:
 
  export GREP_OPTIONS='--color=auto'
 
  export GREP_OPTIONS='--color=auto'
To include file line numbers in the output, add "''-n''":
+
To include file line numbers in the output, add {{ic|-n}}:
  alias grep='grep -n --color=auto'  
+
  alias grep='grep -n --color=auto'
 +
 
 +
The environment variable {{ic|GREP_COLORS}} may be used to specify different colors than the defaults.
 +
 
 +
== iconv ==
 +
 
 +
{{ic|iconv}} converts the encoding of characters from one codeset to another.
 +
 
 +
The following command will convert the file {{ic|foo}} from ISO-8859-15 to UTF-8 saving it to {{ic|foo.utf}}:
 +
 
 +
$ iconv -f ISO-8859-15 -t UTF-8 foo >foo.utf
 +
 
 +
See {{ic|man iconv}} for more details.
 +
 
 +
== ip ==
 +
 
 +
[[Wikipedia:Iproute2|ip]] allows you to show information about network devices, IP addresses, routing tables and other objects in the Linux [[Wikipedia:Internet Protocol|IP]] software stack. By appending various commands, you can also manipulate or configure most of these objects.
  
The environment variable '''GREP_COLORS''' may be used to specify different colors than the defaults.
+
{| class="wikitable" border="1" cellpadding="5" cellspacing="0"
 +
! Object !! Purpose !! manpage
 +
|-
 +
| ip addr || protocol address management || ip-address
 +
|-
 +
| ip addrlabel || protocol address label management || ip-addrlabel
 +
|-
 +
| ip l2tp || tunnel ethernet over IP (L2TPv3) || ip-l2tp
 +
|-
 +
| ip link || network device configuration || ip-link
 +
|-
 +
| ip maddr || multicast addresses management || ip-maddress
 +
|-
 +
| ip monitor || watch for netlink messages || ip-monitor
 +
|-
 +
| ip mroute || multicast routing cache management || ip-mroute
 +
|-
 +
| ip mrule || rule in multicast routing policy db
 +
|-
 +
| ip neigh || neighbour/arp tables management|| ip-neighbour
 +
|-
 +
| ip netns || process network namespace management || ip-netns
 +
|-
 +
| ip ntable ||  neighbour table configuration || ip-ntable
 +
|-
 +
| ip route || routing table management || ip-route
 +
|-
 +
| ip rule || routing policy database management || ip-rule
 +
|-
 +
| ip tcp_metrics || management for TCP Metrics || ip-tcp_metrics
 +
|-
 +
| ip tunnel || tunnel configuration || ip-tunnel
 +
|-
 +
| ip tuntap ||  manage TUN/TAP devices
 +
|-
 +
| ip xfrm ||  manage IPSec policies || ip-xfrm
 +
|}
  
== ifconfig ==
+
The help command is available for all objects. For example, typing {{ic|ip addr help}} will show you the command syntax available for the address object.
  
[[Wikipedia:ifconfig|ifconfig]] (''interface configuration'') is a system administration utility in Unix-like operating systems to configure, control, and query TCP/IP network interface parameters from a command line interface (CLI) or in system configuration scripts.
+
The [[Network Configuration]] article shows how the ''ip'' command is used in practice for various common tasks.
  
It is deprecated: the alternative is called [[Configuring_Network|ip]].
+
{{Note|You might be familiar with the [[Wikipedia:ifconfig|ifconfig]] command, which was used in older versions of Linux for interface configuration. It is now deprecated in Arch Linux, you should use ''ip'' instead. }}
  
 
== less ==
 
== less ==
  
[[Wikipedia:less (Unix)|less]] is a terminal pager program used to view the contents of a text file one screen at a time. Whilst similar to other pages such as '''more''' and '''pg''', '''less''' offers a more advanced interface and complete feature-set.[http://www.greenwoodsoftware.com/less/faq.html]
+
[[Wikipedia:less (Unix)|less]] is a terminal pager program used to view the contents of a text file one screen at a time. Whilst similar to other pages such as  
 +
[[Wikipedia:more (command)|more]] and [[Wikipedia:pg (Unix)|pg]], ''less'' offers a more advanced interface and complete [http://www.greenwoodsoftware.com/less/faq.html feature-set].
  
 
=== Colored output through environment variables ===
 
=== Colored output through environment variables ===
Line 80: Line 140:
 
=== Colored output through wrappers ===
 
=== Colored output through wrappers ===
  
You can enable code syntax coloring in '''less'''. First, install {{Pkg|source-highlight}}, then add these lines to your shell configuration file:
+
You can enable code syntax coloring in ''less''. First, install {{Pkg|source-highlight}}, then add these lines to your shell configuration file:
 
{{hc|~/.bashrc|<nowiki>
 
{{hc|~/.bashrc|<nowiki>
 
export LESSOPEN="| /usr/bin/source-highlight-esc.sh %s"
 
export LESSOPEN="| /usr/bin/source-highlight-esc.sh %s"
Line 90: Line 150:
 
Users may now list the compressed files inside of an archive using their pager:
 
Users may now list the compressed files inside of an archive using their pager:
  
{{hc|$ less compressed_file.tar.gz|2=
+
{{hc|$ less ''compressed_file''.tar.gz|2=
 
==> use tar_file:contained_file to view a file in the archive
 
==> use tar_file:contained_file to view a file in the archive
-rw------- username/group  695 2008-01-04 19:24 compressed_file/content1
+
-rw------- ''username''/''group'' 695 2008-01-04 19:24 ''compressed_file''/''content1''
-rw------- username/group  43 2007-11-07 11:17 compressed_file/content2
+
-rw------- ''username''/''group''   43 2007-11-07 11:17 ''compressed_file''/''content2''
compressed_file.tar.gz (END)
+
''compressed_file''.tar.gz (END)
 
}}
 
}}
  
'''lesspipe''' also grants '''less''' the ability of interfacing with files other than archives, serving as an alternative for the specific command associated for that file-type (such as viewing HTML via {{Pkg|html2text}}).
+
''lesspipe'' also grants ''less'' the ability of interfacing with files other than archives, serving as an alternative for the specific command associated for that file-type (such as viewing HTML via {{Pkg|html2text}}).
  
Re-login after installing '''lesspipe''' in order to activate it, or source {{ic|/etc/profile.d/lesspipe.sh}}.
+
Re-login after installing ''lesspipe'' in order to activate it, or source {{ic|/etc/profile.d/lesspipe.sh}}.
  
 
=== Vim as alternative pager ===
 
=== Vim as alternative pager ===
  
[[Vim]] (''visual editor improved'') has a script to view the content of text files, compressed files, binaries, directories. Add the following line to your shell configuration file:
+
[[Vim]] (''visual editor improved'') has a script to view the content of text files, compressed files, binaries, directories. Add the following line to your shell configuration file to use it as a pager:
{{hc|~/.bashrc|2=alias less='/usr/share/vim/vim73/macros/less.sh'}}
+
{{hc|~/.bashrc|2=alias less='/usr/share/vim/vim74/macros/less.sh'}}
 +
 
 +
There is also an alternative to ''less.sh'' macro, which may work as the {{ic|PAGER}} environment variable. Install {{AUR|vimpager-git}} and add the following to your shell configuration file:
 +
{{hc|~/.bashrc|2=
 +
export PAGER='vimpager'
 +
alias less=$PAGER
 +
}}
 +
 
 +
Now programs that use the {{ic|PAGER}} environment variable, like [[git]], will use ''vim'' as pager.
 +
 
 +
== locate ==
 +
 
 +
[[Wikipedia:locate (Unix)|locate]] serves to find files on filesystems. It searches through a prebuilt database of files generated by ''updatedb'' or by a daemon and compressed using incremental encoding. It operates significantly faster than ''find'', but requires regular updating of the database.
 +
 
 +
See the [[locate|main article]].
  
 
== ls ==
 
== ls ==
Line 110: Line 184:
 
[[Wikipedia:ls|ls]] (''list'') is a command to list files in Unix and Unix-like operating systems.
 
[[Wikipedia:ls|ls]] (''list'') is a command to list files in Unix and Unix-like operating systems.
  
Colored output can be enabled with a simple alias. File {{ic|~/.bashrc}} should already have the following entry copied from {{ic|/etc/skel/.bashrc}}:
+
* ''ls'' can list [[File_Permissions_and_Attributes#Viewing_permissions|file permissions]].
alias ls='ls --color=auto'
+
 
The next step will further enhance the colored '''ls''' output; for example, broken (orphan) symlinks will start showing in a red hue. Add the following to your shell configuration file:
+
* Colored output can be enabled with a simple alias. File {{ic|~/.bashrc}} should already have the following entry copied from {{ic|/etc/skel/.bashrc}}:
{{hc|~/.bashrc|eval $(dircolors -b)}}
+
: {{ic|1=alias ls='ls --color=auto'}}
 +
: The next step will further enhance the colored ''ls'' output; for example, broken (orphan) symlinks will start showing in a red hue. Add the following to your shell configuration file:
 +
: {{ic|eval $(dircolors -b)}}
  
 
== man ==
 
== man ==
Line 121: Line 197:
 
== mkdir ==
 
== mkdir ==
  
[[Wikipedia:mkdir_(Unix)|mkdir]] (''make directory'') is a command to create directories. To create a directory and its whole hierarchy, ''-p'' switch is used, if not a error is printed. As users are supposed to know what they want, ''-p'' switch may be used as a default.
+
[[Wikipedia:mkdir|mkdir]] (''make directory'') is a command to create directories.
alias mkdir='mkdir -p -v'
+
* To create a directory and its whole hierarchy, {{ic|-p}} switch is used, if not a error is printed. As users are supposed to know what they want, {{ic|-p}} switch may be used as a default.
The ''-v'' switch make it verbose.
+
: {{bc|1=alias mkdir='mkdir -p -v'}}
{{Note|If you want just a temporary directory a better alternative may be '''mktemp''' (''make termporary''): {{ic|$ mktemp -p}}.
+
: The {{ic|-v}} switch make it verbose.
}}
+
 
 +
* Changing mode of a just created directory using ''chmod'' is not necessary as the {{ic|-m}} option lets you define the access permissions.
 +
 
 +
{{Tip|If you want just a temporary directory a better alternative may be [[Wikipedia:Temporary file|mktemp]] (''make termporary''): {{ic|mktemp -p}}.}}
  
 
== mv ==
 
== mv ==
  
[[Wikipedia:mv_(Unix)|mv]] (''move'') is a command to move and rename files and directories. It could be very dangerous so it is prudent to limit its scope:
+
[[Wikipedia:mv|mv]] (''move'') is a command to move and rename files and directories. It can be very dangerous so it is prudent to limit its scope:
 
  alias mv=' timeout 8 mv -iv'
 
  alias mv=' timeout 8 mv -iv'
This alias suspends '''mv''' after eight seconds, asks confirmation to delete three or more files, lists the operations in progress and does not store itself in the shell history file if the shell is configured to ignore space starting commands.
+
This alias suspends ''mv'' after eight seconds, asks confirmation to delete three or more files, lists the operations in progress and does not store itself in the shell history file if the shell is configured to ignore space starting commands.
  
 
== rm ==
 
== rm ==
  
[[Wikipedia:rm_(Unix)|rm]] (''remove'') is a command to delete files and directories. It could be very dangerous so it is prudent to limit its scope:
+
[[Wikipedia:rm_(Unix)|rm]] (''remove'') is a command to delete files and directories.
alias rm=' timeout 3 rm -Iv --one-file-system'
+
 
This alias suspends '''rm''' after three seconds, asks confirmation to delete three or more files, lists the operations in progress, does not involve more than one file systems and does not store itself in the shell history file if the shell is configured to ignore space starting commands.
+
* It can be very dangerous so it is prudent to limit its scope:
 +
: {{bc|1=alias rm=' timeout 3 rm -Iv --one-file-system'}}
 +
: This alias suspends ''rm'' after three seconds, asks confirmation to delete three or more files, lists the operations in progress, does not involve more than one file systems and does not store itself in the shell history file if the shell is configured to ignore space starting commands. Substitute {{ic|-I}} with {{ic|-i}} if you prefer to confirm even for one file.
 +
: Zsh users may want to put {{ic|noglob}} before {{ic|timeout}} to avoid implicit expansions.
 +
 
 +
* To remove directories known to be empty, use ''rmdir'' as it fails in case of files inside the target.
  
 
== sed ==
 
== sed ==
Line 143: Line 227:
 
[[Wikipedia:sed|sed]] (''stream editor'') is a Unix utility that parses and transforms text.
 
[[Wikipedia:sed|sed]] (''stream editor'') is a Unix utility that parses and transforms text.
  
Here is a handy [http://sed.sourceforge.net/sed1line.txt list] of '''sed''' one-liners examples.
+
Here is a handy [http://sed.sourceforge.net/sed1line.txt list] of ''sed'' one-liners examples.
  
{{Note|More powerful alternatives are awk and even Perl language.}}
+
{{Tip|More powerful alternatives are [[Wikipedia:AWK|AWK]] and even [[Wikipedia:Perl|Perl]] language.}}
 +
 
 +
== seq ==
 +
 
 +
'''seq''' (''sequence'') is a utility for generating a sequence of numbers. Shell built-in alternatives are available, so it is good practice to use them as explained on [[Wikipedia:Seq (Unix)|Wikipedia]].
  
 
== shred ==
 
== shred ==
  
[[Wikipedia:Shred_(Unix)|shred]] is a command to securely delete files and directories. It could be very dangerous so it is prudent to limit its scope:
+
[[Wikipedia:Shred_(Unix)|shred]] is a command to securely delete files and directories. It can be very dangerous so it is prudent to limit its scope:
 
  alias shred=' timeout 3 shred -v'
 
  alias shred=' timeout 3 shred -v'
This alias suspends '''shred''' after three seconds, lists the operations in progress, and does not store itself in the shell history file if the shell is configured to ignore space starting commands.
+
This alias suspends ''shred'' after three seconds, lists the operations in progress, and does not store itself in the shell history file if the shell is configured to ignore space starting commands.
 +
 
 +
Zsh users may want to put {{ic|noglob}} before {{ic|timeout}} to avoid implicit expansions.
  
 
== sudo ==
 
== sudo ==
  
 
[[Wikipedia:Sudo|Sudo]] (''as superuser do'') is a program for Unix-like computer operating systems that allows users to run programs with the security privileges of another user (normally the superuser, or root). See [[Sudo]].
 
[[Wikipedia:Sudo|Sudo]] (''as superuser do'') is a program for Unix-like computer operating systems that allows users to run programs with the security privileges of another user (normally the superuser, or root). See [[Sudo]].
 +
 +
== Permissions related utilities ==
 +
 +
* [[Wikipedia:chmod|chmod]] (''change mode'') is the name of a Unix shell command and a system call, which both change the access permissions to file system objects (including files and directories), as well as specifying special flags.
 +
 +
* [[Wikipedia:chown|chown]] (''change owner'') is used on Unix-like systems to change the owner of a file.
 +
 +
* [[Wikipedia:chattr|chattr]] (''change attributes'') is a command in the Linux operating system that allows a user to set certain attributes on a file residing on many Linux filesystems.
 +
 +
* [[Wikipedia:lsattr|lsattr]] (''list attributes'') is a command-line program for listing the attributes on a Linux extended file system.
 +
 +
* {{ic|ls -l}} lists files attributes.
 +
 +
These utilities are explained in the [[File Permissions and Attributes]] article. More advanced permission use cases are satisfied by [[Using File Capabilities Instead Of Setuid|capabilities]] and [[ACL]].
  
 
== See also ==
 
== See also ==
  
* [http://www.reddit.com/r/commandline/comments/19garq/a_sampling_of_coreutils_120/ A sampling of coreutils] [http://www.reddit.com/r/commandline/comments/19ge6v/a_sampling_of_coreutils_2040/ , part 2] [http://www.reddit.com/r/commandline/comments/19j1w3/a_sampling_of_coreutils_4060/ , part 3] - An overview of commands in coreutils
+
* [http://www.reddit.com/r/commandline/comments/19garq/a_sampling_of_coreutils_120/ A sampling of coreutils] [http://www.reddit.com/r/commandline/comments/19ge6v/a_sampling_of_coreutils_2040/ , part 2] [http://www.reddit.com/r/commandline/comments/19j1w3/a_sampling_of_coreutils_4060/ , part 3] - Overview of commands in coreutils

Revision as of 15:02, 18 December 2013

This article deals with so-called core utilities on a GNU/Linux system, such as less, ls, and grep. The scope of this article includes, but is not limited to, those utilities included with the GNU coreutils package. What follows are various tips and tricks and other helpful information related to these utilities.

cat

cat (catenate) is a standard Unix utility that concatenates and lists files.

  • As cat is not a shell built-in, on many occasions you may find more convenient to use a redirection, for example in scripts, or if you care a lot about performance. In fact < file does the same of cat file.
  • To append multiple lines to a file a construct like this one is used:
$ cat << EOF >> path/file
first line
...
last line
EOF
  • If you need to list file lines in reverse order, there is a utility called tac (cat reversed).

cron

cron is a time-based job scheduler in Unix-like computer operating systems.

See the main article.

Note: systemd is able to handle many cron use cases. See the related article.

grep

grep (from ed's g/re/p, global/regular expression/print) is a command line text search utility originally written for Unix. The grep command searches files or standard input globally for lines matching a given regular expression, and prints them to the program's standard output.

  • Remember that grep handles files, so a construct like cat file | grep pattern is replaceable with grep pattern file
  • If you have to grep VCS source code, there is an optimized utility written in Perl and called ack. See the official web site.

Colored output

Beyond aesthetics, grep's color output is immensely useful for learning regexp and grep's functionality.

To use the default colors for grep, write the following entry to your shell configuration file, e.g. if using Bash:

~/.bashrc
alias grep='grep --color=auto'

Alternatively, you can set the GREP_OPTIONS environment variable bearing in mind this may break some scripts that use grep [1]:

export GREP_OPTIONS='--color=auto'

To include file line numbers in the output, add -n:

alias grep='grep -n --color=auto'

The environment variable GREP_COLORS may be used to specify different colors than the defaults.

iconv

iconv converts the encoding of characters from one codeset to another.

The following command will convert the file foo from ISO-8859-15 to UTF-8 saving it to foo.utf:

$ iconv -f ISO-8859-15 -t UTF-8 foo >foo.utf

See man iconv for more details.

ip

ip allows you to show information about network devices, IP addresses, routing tables and other objects in the Linux IP software stack. By appending various commands, you can also manipulate or configure most of these objects.

Object Purpose manpage
ip addr protocol address management ip-address
ip addrlabel protocol address label management ip-addrlabel
ip l2tp tunnel ethernet over IP (L2TPv3) ip-l2tp
ip link network device configuration ip-link
ip maddr multicast addresses management ip-maddress
ip monitor watch for netlink messages ip-monitor
ip mroute multicast routing cache management ip-mroute
ip mrule rule in multicast routing policy db
ip neigh neighbour/arp tables management ip-neighbour
ip netns process network namespace management ip-netns
ip ntable neighbour table configuration ip-ntable
ip route routing table management ip-route
ip rule routing policy database management ip-rule
ip tcp_metrics management for TCP Metrics ip-tcp_metrics
ip tunnel tunnel configuration ip-tunnel
ip tuntap manage TUN/TAP devices
ip xfrm manage IPSec policies ip-xfrm

The help command is available for all objects. For example, typing ip addr help will show you the command syntax available for the address object.

The Network Configuration article shows how the ip command is used in practice for various common tasks.

Note: You might be familiar with the ifconfig command, which was used in older versions of Linux for interface configuration. It is now deprecated in Arch Linux, you should use ip instead.

less

less is a terminal pager program used to view the contents of a text file one screen at a time. Whilst similar to other pages such as more and pg, less offers a more advanced interface and complete feature-set.

Colored output through environment variables

Add the following lines to your shell configuration file:

~/.bashrc
export LESS=-R
export LESS_TERMCAP_me=$(printf '\e[0m')
export LESS_TERMCAP_se=$(printf '\e[0m')
export LESS_TERMCAP_ue=$(printf '\e[0m')
export LESS_TERMCAP_mb=$(printf '\e[1;32m')
export LESS_TERMCAP_md=$(printf '\e[1;34m')
export LESS_TERMCAP_us=$(printf '\e[1;32m')
export LESS_TERMCAP_so=$(printf '\e[1;44;1m')

Change values as you like. References: ANSI escape code.

Colored output through wrappers

You can enable code syntax coloring in less. First, install source-highlight, then add these lines to your shell configuration file:

~/.bashrc
export LESSOPEN="| /usr/bin/source-highlight-esc.sh %s"
export LESS='-R '

Frequent users of the command line interface might want to install lesspipe.

Users may now list the compressed files inside of an archive using their pager:

$ less compressed_file.tar.gz
==> use tar_file:contained_file to view a file in the archive
-rw------- username/group  695 2008-01-04 19:24 compressed_file/content1
-rw------- username/group   43 2007-11-07 11:17 compressed_file/content2
compressed_file.tar.gz (END)

lesspipe also grants less the ability of interfacing with files other than archives, serving as an alternative for the specific command associated for that file-type (such as viewing HTML via html2text).

Re-login after installing lesspipe in order to activate it, or source /etc/profile.d/lesspipe.sh.

Vim as alternative pager

Vim (visual editor improved) has a script to view the content of text files, compressed files, binaries, directories. Add the following line to your shell configuration file to use it as a pager:

~/.bashrc
alias less='/usr/share/vim/vim74/macros/less.sh'

There is also an alternative to less.sh macro, which may work as the PAGER environment variable. Install vimpager-gitAUR and add the following to your shell configuration file:

~/.bashrc
export PAGER='vimpager'
alias less=$PAGER

Now programs that use the PAGER environment variable, like git, will use vim as pager.

locate

locate serves to find files on filesystems. It searches through a prebuilt database of files generated by updatedb or by a daemon and compressed using incremental encoding. It operates significantly faster than find, but requires regular updating of the database.

See the main article.

ls

ls (list) is a command to list files in Unix and Unix-like operating systems.

  • Colored output can be enabled with a simple alias. File ~/.bashrc should already have the following entry copied from /etc/skel/.bashrc:
alias ls='ls --color=auto'
The next step will further enhance the colored ls output; for example, broken (orphan) symlinks will start showing in a red hue. Add the following to your shell configuration file:
eval $(dircolors -b)

man

man (manual page) is a form of online software documentation usually found on a Unix or Unix-like operating system. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts. See Man Pages.

mkdir

mkdir (make directory) is a command to create directories.

  • To create a directory and its whole hierarchy, -p switch is used, if not a error is printed. As users are supposed to know what they want, -p switch may be used as a default.
alias mkdir='mkdir -p -v'
The -v switch make it verbose.
  • Changing mode of a just created directory using chmod is not necessary as the -m option lets you define the access permissions.
Tip: If you want just a temporary directory a better alternative may be mktemp (make termporary): mktemp -p.

mv

mv (move) is a command to move and rename files and directories. It can be very dangerous so it is prudent to limit its scope:

alias mv=' timeout 8 mv -iv'

This alias suspends mv after eight seconds, asks confirmation to delete three or more files, lists the operations in progress and does not store itself in the shell history file if the shell is configured to ignore space starting commands.

rm

rm (remove) is a command to delete files and directories.

  • It can be very dangerous so it is prudent to limit its scope:
alias rm=' timeout 3 rm -Iv --one-file-system'
This alias suspends rm after three seconds, asks confirmation to delete three or more files, lists the operations in progress, does not involve more than one file systems and does not store itself in the shell history file if the shell is configured to ignore space starting commands. Substitute -I with -i if you prefer to confirm even for one file.
Zsh users may want to put noglob before timeout to avoid implicit expansions.
  • To remove directories known to be empty, use rmdir as it fails in case of files inside the target.

sed

sed (stream editor) is a Unix utility that parses and transforms text.

Here is a handy list of sed one-liners examples.

Tip: More powerful alternatives are AWK and even Perl language.

seq

seq (sequence) is a utility for generating a sequence of numbers. Shell built-in alternatives are available, so it is good practice to use them as explained on Wikipedia.

shred

shred is a command to securely delete files and directories. It can be very dangerous so it is prudent to limit its scope:

alias shred=' timeout 3 shred -v'

This alias suspends shred after three seconds, lists the operations in progress, and does not store itself in the shell history file if the shell is configured to ignore space starting commands.

Zsh users may want to put noglob before timeout to avoid implicit expansions.

sudo

Sudo (as superuser do) is a program for Unix-like computer operating systems that allows users to run programs with the security privileges of another user (normally the superuser, or root). See Sudo.

Permissions related utilities

  • chmod (change mode) is the name of a Unix shell command and a system call, which both change the access permissions to file system objects (including files and directories), as well as specifying special flags.
  • chown (change owner) is used on Unix-like systems to change the owner of a file.
  • chattr (change attributes) is a command in the Linux operating system that allows a user to set certain attributes on a file residing on many Linux filesystems.
  • lsattr (list attributes) is a command-line program for listing the attributes on a Linux extended file system.
  • ls -l lists files attributes.

These utilities are explained in the File Permissions and Attributes article. More advanced permission use cases are satisfied by capabilities and ACL.

See also