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[[Category:System administration]]
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[[Category:Command-line]]
[[Category:Command shells]]
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[[fa:Core utilities]]
[[it:Core Utilities]]
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[[es:Core utilities]]
[[zh-CN:Core Utilities]]
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[[it:Core utilities]]
{{Article summary start}}
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[[ja:Core Utilities]]
{{Article summary text|Tips and tricks related to so-called ''core'' utilities on a GNU/Linux system.}}
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[[ko:Core utilities]]
{{Article summary heading|Related}}
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[[pt:Core utilities]]
{{Article summary wiki|Bash}}: improved Bourne shell, Linux standard
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[[ru:Core utilities]]
{{Article summary wiki|Zsh}}: improved Bourne/C shell, very good as interactive shell
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[[zh-hans:Core utilities]]
{{Article summary wiki|General Recommendations}}
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[[zh-hant:Core utilities]]
{{Article summary wiki|GNU Project}}
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{{Related articles start}}
{{Article summary end}}
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{{Related|Command-line shell}}
 +
{{Related|General recommendations}}
 +
{{Related|GNU Project}}
 +
{{Related|sudo}}
 +
{{Related|cron}}
 +
{{Related|man page}}
 +
{{Related|Securely wipe disk#shred}}
 +
{{Related|File permissions and attributes}}
 +
{{Related|Color output in console}}
 +
{{Related|Archiving and compression tools}}
 +
{{Related articles 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.
 
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.
  
== cat ==
+
Most command-line interfaces are documented in [[man page]]s, [[GNU]] commands tend to be documented in {{man|1|info}} pages, some [[shell]]s provide a {{ic|help}} command for [[shell]]-builtin commands. Additionally most commands print their usage when run with the {{ic|--help}} argument.
  
[[Wikipedia:cat_(Unix)|cat]] (''catenate'') is a standard Unix utility that concatenates and lists files.
+
== File management ==
  
* As ''cat'' is not a shell built-in, in 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''}}.
+
{| class="wikitable"
 +
! Command
 +
! Description
 +
! Manual page
 +
! Example
 +
|-
 +
| cd
 +
| Change directory (shell built-in command)
 +
| {{man|1p|cd}}
 +
| cd /etc/pacman.d
 +
|-
 +
| mkdir
 +
| Create a directory
 +
| {{man|1|mkdir}}
 +
| mkdir ~/newfolder
 +
|-
 +
| rmdir
 +
| Remove empty directory
 +
| {{man|1|rmdir}}
 +
| rmdir ~/emptyfolder
 +
|-
 +
| rm
 +
| Remove a file
 +
| {{man|1|rm}}
 +
| rm ~/file.txt
 +
|-
 +
| rm -r
 +
| Remove directory and contents
 +
|
 +
| rm -r ~/.cache
 +
|-
 +
| ls
 +
| List files
 +
| {{man|1|ls}}
 +
| ls *.mkv
 +
|-
 +
| ls -a
 +
| List hidden files
 +
|
 +
| ls -a /home/archie
 +
|-
 +
| ls -al
 +
| List hidden files and file properties
 +
|
 +
|
 +
|-
 +
| mv
 +
| Move a file
 +
| {{man|1|mv}}
 +
| mv ~/compressed.zip ~/archive/compressed2.zip
 +
|-
 +
| cp
 +
| Copy a file
 +
| {{man|1|cp}}
 +
| cp ~/.bashrc ~/.bashrc.bak
 +
|-
 +
| chmod +x
 +
| Make a file [[executable]]
 +
| {{man|1|chmod}}
 +
| chmod +x ~/.local/bin/myscript.sh
 +
|-
 +
| cat
 +
| Show file contents
 +
| {{man|1|cat}}
 +
| cat /etc/hostname
 +
|-
 +
| find
 +
| Search for a file
 +
| {{man|1|find}}
 +
| find ~ -name myfile
 +
|}
  
* To append multiple lines to a file a construct like this one is used:
+
=== ls ===
 +
 
 +
[[Wikipedia:ls|ls]] lists directory contents.
 +
 
 +
See {{ic|info ls}} or [https://www.gnu.org/software/coreutils/manual/html_node/ls-invocation.html#ls-invocation the online manual] for more information.
 +
 
 +
[https://the.exa.website exa] is a modern, and more user friendly alternative to {{ic|ls}} and {{ic|tree}}, that has more features, such as displaying [[Git]] modifications along with filenames, colouring differently each columnn in {{ic|--long}} mode, or displaying {{ic|--long}} mode metadata along with a {{ic|tree}} view. {{Pkg|exa}}
 +
==== Long format ====
 +
 
 +
The {{ic|-l}} option displays some metadata, for example:
 +
 
 +
{{hc|$ ls -l ''/path/to/directory''|
 +
total 128
 +
drwxr-xr-x 2 archie users  4096 Jul  5 21:03 Desktop
 +
drwxr-xr-x 6 archie users  4096 Jul  5 17:37 Documents
 +
drwxr-xr-x 2 archie users  4096 Jul  5 13:45 Downloads
 +
-rw-rw-r-- 1 archie users  5120 Jun 27 08:28 customers.ods
 +
-rw-r--r-- 1 archie users  3339 Jun 27 08:28 todo
 +
-rwxr-xr-x 1 archie users  2048 Jul  6 12:56 myscript.sh
 +
}}
 +
 
 +
The {{ic|total}} value represents the total disk allocation for the files in the directory, by default in number of blocks.
 +
 
 +
Below, each file and subdirectory is represented by a line divided into 7 metadata fields, in the following order:
 +
 
 +
* type and permissions:
 +
** the first character is the entry type, see {{ic|info ls -n "What information is listed"}} for an explanation of all the possible types; for example:
 +
*** {{ic|-}} denotes a normal file;
 +
*** {{ic|d}} denotes a directory, i.e. a folder containing other files or folders;
 +
*** {{ic|p}} denotes a named pipe (aka FIFO);
 +
*** {{ic|l}} denotes a symbolic link;
 +
** the remaining characters are the entry's [[permissions]];
 +
* number of [[Wikipedia:Hard link|hard links]] for the entity; files will have at least 1, i.e. the showed reference itself; folders will have at least 2: the showed reference, the self-referencing {{ic|.}} entry, and then a {{ic|..}} entry in each of its subfolders;
 +
* owner [[user]] name;
 +
* [[group]] name;
 +
* size;
 +
* last modification timestamp;
 +
* entity name.
 +
 
 +
==== File names containing spaces enclosed in quotes ====
 +
 
 +
By default, file and directory names that contain spaces are displayed surrounded by single quotes. To change this behavior use the {{ic|-N}} or {{ic|1=--quoting-style=literal}} options. Alternatively, set the {{ic|QUOTING_STYLE}} [[environment variable]] to {{ic|literal}}. [https://unix.stackexchange.com/questions/258679/why-is-ls-suddenly-surrounding-items-with-spaces-in-single-quotes]
 +
 
 +
=== cat ===
 +
 
 +
[[Wikipedia:cat_(Unix)|cat]] is a standard Unix utility that concatenates files to standard output.
 +
 
 +
* Because ''cat'' is not built into the shell, on many occasions you may find it 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 as {{ic|cat ''file''}}.
 +
 
 +
* ''cat'' can work with multiple lines:
  
 
{{bc|
 
{{bc|
Line 30: Line 159:
 
}}
 
}}
  
* If you need to cat file lines in reverse order, there is a utility called [[Wikipedia:tac (Unix)|tac]] (''cat'' reversed).
+
Alternatively, using {{ic|printf}}:
 +
 
 +
{{bc|
 +
$ printf '%s\n' 'first line' ... 'last line'
 +
}}
 +
 
 +
* If you need to list file lines in reverse order, there is a coreutil command called [[Wikipedia:tac (Unix)|tac]] (''cat'' reversed).
 +
 
 +
=== less ===
 +
 
 +
{{Expansion|less is a complex beast, and this section should explain some of the basic less commands}}
 +
 
 +
[[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 pagers such as [[Wikipedia:more (command)|more]] and the [https://git.kernel.org/cgit/utils/util-linux/util-linux.git/tree/Documentation/deprecated.txt deprecated] [[Wikipedia:pg (Unix)|pg]], ''less'' offers a more advanced interface and complete [http://www.greenwoodsoftware.com/less/faq.html feature-set].
 +
 
 +
See [[List of applications#Terminal pagers]] for alternatives.
 +
 
 +
==== Vim as alternative pager ====
 +
 
 +
[[Vim]] includes a script to view the content of text files, compressed files, binaries and directories. Add the following line to your shell configuration file to use it as a pager:
 +
{{hc|~/.bashrc|2=alias less='/usr/share/vim/vim80/macros/less.sh'}}
 +
 
 +
There is also an alternative to the ''less.sh'' macro, which may work as the {{ic|PAGER}} environment variable. Install {{Pkg|vimpager}} 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.
 +
 
 +
=== mkdir ===
 +
 
 +
[[Wikipedia:mkdir|mkdir]] makes directories.
 +
 
 +
To create a directory and its whole hierarchy, the {{ic|-p}} switch is used, otherwise an error is printed.
 +
 
 +
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 just want a temporary directory, a better alternative may be [[Wikipedia:Temporary file|mktemp]]: {{ic|mktemp -d}}}}
 +
 
 +
=== mv ===
 +
 
 +
[[Wikipedia:mv|mv]] moves and renames files and directories.
 +
 
 +
{{Note|"Security aliases" are dangerous because you get used to them, resulting in potential data loss when you use another system / user that doesn't have these aliases.}}
 +
 
 +
To limit potential damage caused by the command, use an alias:
 +
 
 +
alias mv='mv -iv'
 +
 
 +
This alias asks for confirmation before overwriting any existing files and lists the operations in progress.
 +
 
 +
=== rm ===
 +
 
 +
[[Wikipedia:rm_(Unix)|rm]] removes files or directories.
  
== grep ==
+
{{Note|"Security aliases" are dangerous because you get used to them, resulting in potential data loss when you use another system / user that doesn't have these aliases.}}
  
[[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.
+
To limit potential damage caused by the command, use an alias:
* Remember that ''grep'' handles files, so a construct like {{ic|$ cat ''file'' <nowiki>|</nowiki> grep ''pattern''}} 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].
+
alias rm='rm -Iv --one-file-system'
  
=== Colored output ===
+
This alias asks confirmation to delete three or more files, lists the operations in progress, does not involve more than one file systems. Substitute {{ic|-I}} with {{ic|-i}} if you prefer to confirm even for one file.
  
Beyond aesthetics, ''grep''&#39;s color output is immensely useful for learning [[Wikipedia:regexp|regexp]] and ''grep''&#39;s functionality.
+
Zsh users may want to prefix {{ic|noglob}} to avoid implicit expansions.
  
To use the default colors for ''grep'', write the following entry to your shell configuration file, e.g. if using [[Bash]]:
+
To remove directories believed to be empty, use ''rmdir'' as it fails if there are files inside the target.
{{hc|~/.bashrc|2=alias grep='grep --color=auto'}}
 
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'
 
To include file line numbers in the output, add {{ic|-n}}:
 
alias grep='grep -n --color=auto'
 
  
The environment variable {{ic|GREP_COLORS}} may be used to specify different colors than the defaults.
+
=== chmod ===
  
== ifconfig ==
+
See [[File permissions and attributes#Changing permissions]].
{{Out of date|Rewrite focusing on ''ip''.}}
 
  
[[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.
+
=== chown ===
  
It is deprecated: the alternative is called [[Configuring_Network|ip]].
+
See [[File permissions and attributes#Changing ownership]].
  
== less ==
+
=== find ===
  
[[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
+
''find'' is part of the {{Pkg|findutils}} package, which belongs to the {{Grp|base}} package group.  
[[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 ===
+
{{Tip|{{Pkg|fd}} is a simple, fast and user-friendly alternative to {{ic|find}} that provides more sensible defaults (e.g. ignores hidden files, directories and {{ic|.gitignore}}'d files, {{ic|fd PATTERN}} instead of {{ic|find -iname '*PATTERN*'}}). It features colorized output (similar to {{ic|ls}}), Unicode awareness, regular expressions and more.}}
  
Add the following lines to your shell configuration file:
+
One would probably expect a ''find'' command to take as argument a file name and search the filesystem for files matching that name. For a program that does exactly that see [[#locate]] below.
  
{{hc|~/.bashrc|2=
+
Instead, find takes a set of directories and matches each file under them against a set of expressions. This design allows for some very powerful "one-liners" that would not be possible using the "intuitive" design described above. See [[GregsWiki:UsingFind]] for usage details.
export LESS=-R
+
 
export LESS_TERMCAP_me=$(printf '\e[0m')
+
=== locate ===
export LESS_TERMCAP_se=$(printf '\e[0m')
+
 
export LESS_TERMCAP_ue=$(printf '\e[0m')
+
[[Install]] the {{Pkg|mlocate}} package. The package contains an {{ic|updatedb.timer}} unit, which invokes a database update each day. The timer is enabled right after installation, [[start]] it manually if you want to use it before reboot. You can also manually run ''updatedb'' as root at any time. By default, paths such as {{ic|/media}} and {{ic|/mnt}} are ignored, so ''locate'' may not discover files on external devices. See {{man|8|updatedb}} for details.
export LESS_TERMCAP_mb=$(printf '\e[1;32m')
+
 
export LESS_TERMCAP_md=$(printf '\e[1;34m')
+
The ''locate'' command is a common Unix tool for quickly finding files by name. It offers speed improvements over the [[wikipedia:Find (Unix)|find]] tool by searching a pre-constructed database file, rather than the filesystem directly. The downside of this approach is that changes made since the construction of the database file cannot be detected by ''locate''.
export LESS_TERMCAP_us=$(printf '\e[1;32m')
+
 
export LESS_TERMCAP_so=$(printf '\e[1;44;1m')
+
Before ''locate'' can be used, the database will need to be created. To do this, execute {{ic|updatedb}} as root.
 +
 
 +
See also [http://jvns.ca/blog/2015/03/05/how-the-locate-command-works-and-lets-rewrite-it-in-one-minute/ How locate works and rewrite it in one minute].
 +
 
 +
== Text streams ==
 +
 
 +
=== grep ===
 +
 
 +
[[Wikipedia:grep|grep]] is a command line text search utility originally written for Unix. The ''grep'' command searches files or standard input for lines matching a given regular expression, and prints these lines to standard output.
 +
 
 +
* Remember that ''grep'' handles files, so a construct like {{ic|cat ''file'' {{!}} grep ''pattern''}} is replaceable with {{ic|grep ''pattern'' ''file''}}
 +
* There are ''grep'' alternatives optimized for VCS source code, such as {{Pkg|ripgrep}}, {{Pkg|the_silver_searcher}}, and {{Pkg|ack}}.
 +
* To include file line numbers in the output, use the {{ic|-n}} option.
 +
* ''grep'' can also be used for hexadecimal search in a binary file, to look for let say the {{ic|A1 F2}} sequence in a file, the command line is: {{bc|1=$ LANG=C grep --text --perl-regexp "\xA1\xF2" ''/path/to/file''}}
 +
 
 +
{{Note|Some commands send their output to {{man|3|stderr}}, and grep has no apparent effect. In this case, redirect ''stderr'' to ''stdout'' with {{ic|''command'' 2>&1 {{!}} grep ''args''}} or (for Bash 4) {{ic|''command'' {{!}}& grep ''args''}}. See also [http://www.tldp.org/LDP/abs/html/io-redirection.html I/O Redirection].}}
 +
 
 +
For color support, see [[Color output in console#grep]].
 +
 
 +
See {{man|1|grep}} for more details.
 +
 
 +
=== sed ===
 +
 
 +
[[Wikipedia:sed|sed]] is stream editor for filtering and transforming text.
 +
 
 +
Here is a handy [http://sed.sourceforge.net/sed1line.txt list] of ''sed'' one-liners examples.
 +
 
 +
{{Tip|More powerful alternatives are [[#awk|awk]] and the [[Perl]] language.}}
 +
 
 +
=== awk ===
 +
 
 +
[[Wikipedia:AWK|AWK]] is a pattern scanning and processing language. There are multiple implementations:
 +
 
 +
* {{App|gawk|GNU version of awk, see {{man|1|gawk}}.|https://www.gnu.org/software/gawk/|{{Pkg|gawk}} (part of {{Grp|base}})}}
 +
* {{App|nawk|The one, true implementation of AWK, see {{man|1|nawk}}.|https://www.cs.princeton.edu/~bwk/btl.mirror/|{{Pkg|nawk}}}}
 +
* {{App|mawk|A very fast AWK implementation.|http://invisible-island.net/mawk/|{{AUR|mawk}}}}
 +
* [[BusyBox]] also includes an AWK implementation.
 +
 
 +
=== pv ===
 +
 
 +
{{Remove|Not part of {{pkg|coreutils}}, {{pkg|util-linux}}, or {{grp|base}}. Is it a "core utility"?}}
 +
 
 +
You can use {{Pkg|pv}} to monitor the progress of data through a pipeline, for example:
 +
 
 +
# dd if=''/source/filestream'' | pv -''monitor_options'' -s ''size_of_file'' | dd of=''/destination/filestream''
 +
 
 +
In most cases {{ic|pv}} functions as a drop-in replacement for {{ic|cat}}.
 +
 
 +
== System administration ==
 +
 
 +
{| class="wikitable"
 +
! Command
 +
! Description
 +
! Manual page
 +
! Example
 +
|-
 +
| mount
 +
| Mount a partition
 +
| {{man|8|mount}}
 +
| mount /dev/sdc1 /media/usb
 +
|-
 +
| df -h
 +
| Show remaining space on all partitions
 +
| {{man|1|df}}
 +
|
 +
|-
 +
| ps -A
 +
| Show all running processes
 +
| {{man|1|ps}}
 +
|
 +
|-
 +
| killall
 +
| Kill all running instances of a process
 +
| {{man|1|killall}}
 +
|
 +
|-
 +
| ss -at
 +
| Display a list of open TCP sockets
 +
| {{man|8|ss}}
 +
|
 +
|}
 +
 
 +
=== sudo ===
 +
 
 +
See [[Sudo]].
 +
 
 +
=== which ===
 +
 
 +
[[wikipedia:Which_(Unix)|which]] shows the full path of shell commands. In the following example the full path of {{ic|ssh}} is used as an argument for {{ic|journalctl}}:
 +
 
 +
# journalctl $(which sshd)
 +
 
 +
=== lsblk ===
 +
 
 +
{{man|8|lsblk}} will show all available [[Wikipedia:Device file#Block devices|block devices]] along with their partitioning schemes, for example:
 +
 
 +
{{hc|$ lsblk -f|
 +
NAME  FSTYPE  LABEL      UUID                                MOUNTPOINT
 +
sda
 +
├─sda1 vfat                C4DA-2C4D                            /boot
 +
├─sda2 swap                5b1564b2-2e2c-452c-bcfa-d1f572ae99f2 [SWAP]
 +
└─sda3 ext4                56adc99b-a61e-46af-aab7-a6d07e504652 /
 
}}
 
}}
  
Change values as you like. References: [[Wikipedia:ANSI_escape_code#Colors|ANSI escape code]].
+
The beginning of the device name specifies the type of block device. Most modern storage devices (e.g. hard disks, [[SSD]]s and USB flash drives) are recognised as SCSI disks ({{ic|sd}}). The type is followed by a lower-case letter starting from {{ic|a}} for the first device ({{ic|sda}}), {{ic|b}} for the second device ({{ic|sdb}}), and so on. ''Existing'' partitions on each device will be listed with a number starting from {{ic|1}} for the first partition ({{ic|sda1}}), {{ic|2}} for the second ({{ic|sda2}}), and so on. In the example above, only one device is available ({{ic|sda}}), and that device has three partitions ({{ic|sda1}} to {{ic|sda3}}), each with a different [[file system]].
  
=== Colored output through wrappers ===
+
Other common block device types include for example {{ic|mmcblk}} for memory cards and {{ic|nvme}} for [[NVMe]] devices. Unknown types can be searched in the [https://www.kernel.org/doc/html/latest/admin-guide/devices.html kernel documentation].
  
You can enable code syntax coloring in ''less''. First, install {{Pkg|source-highlight}}, then add these lines to your shell configuration file:
+
=== ip ===
{{hc|~/.bashrc|<nowiki>
 
export LESSOPEN="| /usr/bin/source-highlight-esc.sh %s"
 
export LESS='-R '
 
</nowiki>}}
 
  
Frequent users of the command line interface might want to install {{Pkg|lesspipe}}.
+
[[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.
  
Users may now list the compressed files inside of an archive using their pager:
+
{{Note|The ''ip'' utility is provided by the {{Pkg|iproute2}} package, which is included in the {{Grp|base}} group.}}
  
{{hc|$ less ''compressed_file''.tar.gz|2=
+
{| class="wikitable"
==> use tar_file:contained_file to view a file in the archive
+
! Object !! Purpose !! Manual page
-rw------- ''username''/''group'' 695 2008-01-04 19:24 ''compressed_file''/''content1''
+
|-
-rw------- ''username''/''group''   43 2007-11-07 11:17 ''compressed_file''/''content2''
+
| ip addr || protocol address management || {{man|8|ip-address}}
''compressed_file''.tar.gz (END)
+
|-
}}
+
| ip addrlabel || protocol address label management || {{man|8|ip-addrlabel}}
 +
|-
 +
| ip l2tp || tunnel Ethernet over IP (L2TPv3) || {{man|8|ip-l2tp}}
 +
|-
 +
| ip link || network device configuration || {{man|8|ip-link}}
 +
|-
 +
| ip maddr || multicast addresses management || {{man|8|ip-maddress}}
 +
|-
 +
| ip monitor || watch for netlink messages || {{man|8|ip-monitor}}
 +
|-
 +
| ip mroute || multicast routing cache management || {{man|8|ip-mroute}}
 +
|-
 +
| ip mrule || rule in multicast routing policy db ||
 +
|-
 +
| ip neigh || neighbour/ARP tables management || {{man|8|ip-neighbour}}
 +
|-
 +
| ip netns || process network namespace management || {{man|8|ip-netns}}
 +
|-
 +
| ip ntable || neighbour table configuration || {{man|8|ip-ntable}}
 +
|-
 +
| ip route || routing table management || {{man|8|ip-route}}
 +
|-
 +
| ip rule || routing policy database management || {{man|8|ip-rule}}
 +
|-
 +
| ip tcp_metrics || management for TCP Metrics || {{man|8|ip-tcp_metrics}}
 +
|-
 +
| ip tunnel || tunnel configuration || {{man|8|ip-tunnel}}
 +
|-
 +
| ip tuntap || manage TUN/TAP devices ||
 +
|-
 +
| ip xfrm || manage IPsec policies || {{man|8|ip-xfrm}}
 +
|}
 +
 
 +
The {{ic|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. For advanced usage see the [http://www.policyrouting.org/iproute2.doc.html iproute2 documentation].
 +
 
 +
The [[Network configuration]] article shows how the ''ip'' command is used in practice for various common tasks.
 +
 
 +
{{Note|You might be familiar with the [[Wikipedia:ifconfig|ifconfig]] command, which is deprecated in Arch Linux; use ''ip'' instead. }}
 +
 
 +
=== ss ===
 +
 
 +
''ss'' is a utility to investigate network ports and is part of the {{Pkg|iproute2}} package in the {{Grp|base}} group. It has a similar functionality to the [https://www.archlinux.org/news/deprecation-of-net-tools/ deprecated] netstat utility.
 +
 
 +
Common usage includes:
 +
 
 +
Display all TCP Sockets with service names:
 +
$ ss -at
 +
 
 +
Display all TCP Sockets with port numbers:
 +
$ ss -atn
 +
 
 +
Display all UDP Sockets:
 +
$ ss -au
 +
 
 +
For more information see {{man|8|ss}} or {{ic|ss.html}} from the {{Pkg|iproute2}} package.
 +
 
 +
== Miscellaneous ==
 +
 
 +
{| class="wikitable"
 +
! Command
 +
! Description
 +
! Manual page
 +
! Example
 +
|-
 +
| strings
 +
| Show printable characters in binary files
 +
| {{man|1|strings}}
 +
| strings /usr/bin/free
 +
|}
 +
 
 +
=== dd ===
 +
 
 +
[[Wikipedia:dd (Unix)|dd]] is a utility for Unix and Unix-like operating systems whose primary purpose is to convert and copy a file.
 +
 
 +
Similarly to ''cp'', by default ''dd'' makes a bit-to-bit copy of the file, but with lower-level I/O flow control features.
 +
 
 +
Some notable applications of ''dd'' are:
 +
 
 +
* [[Disk cloning#Using dd]],
 +
 
 +
* Binary file patching: let say one wants to replace offset {{ic|0x123AB}} of a file with the {{ic|FF C0 14}} hexadecimal sequence, this can be done with the command line: {{bc|1=# printf '\xff\xc0\x14' {{!}} dd seek=$((0x123AB)) conv=notrunc bs=1 of=''/path/to/file''}}
 +
 
 +
For more information see {{man|1|dd}} or the [https://www.gnu.org/software/coreutils/dd full documentation].
 +
 
 +
{{Tip|By default, ''dd'' outputs nothing until the task has finished. To monitor the progress of the operation, add the {{ic|1=status=progress}} option to the command.}}
 +
{{Warning|One should be extremely cautious using ''dd'', as with any command of this kind it can destroy data irreversibly.}}
 +
 
 +
=== iconv ===
 +
 
 +
''iconv'' converts the encoding of characters from one codeset to another.
  
''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}}).
+
The following command will convert the file {{ic|''foo''}} from ISO-8859-15 to UTF-8, saving it to {{ic|''foo''.utf}}:
  
Re-login after installing ''lesspipe'' in order to activate it, or source {{ic|/etc/profile.d/lesspipe.sh}}.
+
$ iconv -f ISO-8859-15 -t UTF-8 ''foo'' > ''foo''.utf
  
=== Vim as alternative pager ===
+
See {{man|1|iconv}} for more details.
  
[[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:
+
==== Convert a file in place ====
{{hc|~/.bashrc|2=alias less='/usr/share/vim/vim73/macros/less.sh'}}
 
  
== ls ==
+
{{Tip|You can use {{pkg|recode}} instead of iconv if you do not want to touch the mtime.}}
 +
Unlike [[#sed|sed]], ''iconv'' does not provide an option to convert a file in place. However, {{ic|sponge}} from the {{pkg|moreutils}} package can help:
  
[[Wikipedia:ls|ls]] (''list'') is a command to list files in Unix and Unix-like operating systems.
+
$ iconv -f WINDOWS-1251 -t UTF-8 ''foobar''.txt | sponge ''foobar''.txt
  
Colored output can be enabled with a simple alias. File {{ic|~/.bashrc}} should already have the following entry copied from {{ic|/etc/skel/.bashrc}}:
+
See {{man|1|sponge}} for details.
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:
 
{{hc|~/.bashrc|eval $(dircolors -b)}}
 
  
== man ==
+
=== od ===
  
[[Wikipedia:Man page|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]].
+
The [[Wikipedia:od (Unix)|od]] (''o''ctal ''d''ump) command is useful for visualizing data that is not in a human-readable format, like the executable code of a program, or the contents of an unformatted device. See the [https://www.gnu.org/software/coreutils/manual/html_node/od-invocation.html#od-invocation manual] for more information.
  
== mkdir ==
+
=== seq ===
  
[[Wikipedia:mkdir_(Unix)|mkdir]] (''make directory'') is a command to create directories. 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.
+
''seq'' prints 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]].
alias mkdir='mkdir -p -v'
 
The {{ic|-v}} switch make it verbose.
 
{{Tip|If you want just a temporary directory a better alternative may be [[Wikipedia:Temporary file|mktemp]] (''make termporary''): {{ic|mktemp -p}}.
 
}}
 
  
== mv ==
+
=== tar ===
  
[[Wikipedia:mv_(Unix)|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:
+
As an early Unix archiving format, .tar files—known as "tarballs"—are widely used for packaging in Unix-like operating systems. Both [[pacman]] and [[AUR]] packages are compressed tarballs, and Arch uses [[GNU Project|GNU's]] ''tar'' program by default.  
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 ==
+
For ''.tar'' archives, ''tar'' by default will extract the file according to its extension:
  
[[Wikipedia:rm_(Unix)|rm]] (''remove'') is a command to delete files and directories. It can be very dangerous so it is prudent to limit its scope:
+
$ tar xvf ''file.EXTENSION''
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.
 
  
== sed ==
+
Forcing a given format:
  
[[Wikipedia:sed|sed]] (''stream editor'') is a Unix utility that parses and transforms text.
+
{| class="wikitable"
 +
!File Type    !! Extraction Command
 +
|-
 +
|{{ic|''file''.tar}}    || {{Ic|tar xvf ''file''.tar}}
 +
|-
 +
|{{ic|''file''.tgz}}    || {{Ic|tar xvzf ''file''.tgz}}
 +
|-
 +
|{{ic|''file''.tar.gz}}  || {{Ic|tar xvzf ''file''.tar.gz}}
 +
|-
 +
|{{ic|''file''.tar.bz}}  || {{Ic|bzip -cd ''file''.bz <nowiki>|</nowiki> tar xvf -}}
 +
|-
 +
|{{ic|''file''.tar.bz2}} || {{Ic|tar xvjf ''file''.tar.bz2}}<br> {{Ic|bzip2 -cd ''file''.bz2 <nowiki>| tar xvf -</nowiki>}}
 +
|-
 +
|{{ic|''file''.tar.xz}}  || {{Ic|tar xvJf ''file''.tar.xz}}<br> {{Ic|xz -cd ''file''.xz <nowiki>| tar xvf -</nowiki>}}
 +
|-
 +
|{{ic|''file''.tar.zst}}  || {{Ic|tar -I zstd xvf ''file''.tar.zst}}
 +
|}
  
Here is a handy [http://sed.sourceforge.net/sed1line.txt list] of ''sed'' one-liners examples.
+
The construction of some of these ''tar'' arguments may be considered legacy, but they are still useful when performing specific operations. See {{man|1|tar}} for details.
  
{{Tip|More powerful alternatives are [[Wikipedia:AWK|AWK]] and even [[Wikipedia:Perl|Perl]] language.}}
+
{{Note|Although GNU's ''tar'' is installed as the default ''tar'' program, official Arch Linux projects like [[pacman]] and [[mkinitcpio]] use ''bsdtar'' from the {{Pkg|libarchive}} package.}}
  
== seq ==
+
=== wipefs ===
  
'''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|Wikipedia]].
+
{{Expansion|Why would you want to erase magic strings?}}
  
== shred ==
+
''wipefs'' can list or erase [[file system]], [[RAID]] or [[partition|partition-table]] signatures (magic strings) from the specified device. It does not erase the file systems themselves nor any other data from the device.
  
[[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:
+
See {{man|8|wipefs}} for more information.
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.
 
  
== sudo ==
+
For example, to erase all signatures from the device {{ic|/dev/sdb}} and create a signature backup {{ic|~/wipefs-sdb-''offset''.bak}} file for each signature:
  
[[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]].
+
# wipefs --all --backup /dev/sdb
  
 
== 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] - Overview of commands in coreutils
+
* [http://pubs.opengroup.org/onlinepubs/9699919799/idx/utilities.html POSIX Utilities]
 +
* [https://www.gnu.org/software/coreutils/manual/coreutils.html GNU Coreutils online documentation]
 +
* [http://www.reddit.com/r/commandline/comments/19garq/a_sampling_of_coreutils_120/ A sampling of coreutils on Reddit] [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
 +
* [https://www.linuxquestions.org/questions/linux-newbie-8/learn-the-dd-command-362506/ Learn the DD command]

Latest revision as of 14:19, 20 July 2018

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.

Most command-line interfaces are documented in man pages, GNU commands tend to be documented in info(1) pages, some shells provide a help command for shell-builtin commands. Additionally most commands print their usage when run with the --help argument.

File management

Command Description Manual page Example
cd Change directory (shell built-in command) cd(1p) cd /etc/pacman.d
mkdir Create a directory mkdir(1) mkdir ~/newfolder
rmdir Remove empty directory rmdir(1) rmdir ~/emptyfolder
rm Remove a file rm(1) rm ~/file.txt
rm -r Remove directory and contents rm -r ~/.cache
ls List files ls(1) ls *.mkv
ls -a List hidden files ls -a /home/archie
ls -al List hidden files and file properties
mv Move a file mv(1) mv ~/compressed.zip ~/archive/compressed2.zip
cp Copy a file cp(1) cp ~/.bashrc ~/.bashrc.bak
chmod +x Make a file executable chmod(1) chmod +x ~/.local/bin/myscript.sh
cat Show file contents cat(1) cat /etc/hostname
find Search for a file find(1) find ~ -name myfile

ls

ls lists directory contents.

See info ls or the online manual for more information.

exa is a modern, and more user friendly alternative to ls and tree, that has more features, such as displaying Git modifications along with filenames, colouring differently each columnn in --long mode, or displaying --long mode metadata along with a tree view. exa

Long format

The -l option displays some metadata, for example:

$ ls -l /path/to/directory
total 128
drwxr-xr-x 2 archie users  4096 Jul  5 21:03 Desktop
drwxr-xr-x 6 archie users  4096 Jul  5 17:37 Documents
drwxr-xr-x 2 archie users  4096 Jul  5 13:45 Downloads
-rw-rw-r-- 1 archie users  5120 Jun 27 08:28 customers.ods
-rw-r--r-- 1 archie users  3339 Jun 27 08:28 todo
-rwxr-xr-x 1 archie users  2048 Jul  6 12:56 myscript.sh

The total value represents the total disk allocation for the files in the directory, by default in number of blocks.

Below, each file and subdirectory is represented by a line divided into 7 metadata fields, in the following order:

  • type and permissions:
    • the first character is the entry type, see info ls -n "What information is listed" for an explanation of all the possible types; for example:
      • - denotes a normal file;
      • d denotes a directory, i.e. a folder containing other files or folders;
      • p denotes a named pipe (aka FIFO);
      • l denotes a symbolic link;
    • the remaining characters are the entry's permissions;
  • number of hard links for the entity; files will have at least 1, i.e. the showed reference itself; folders will have at least 2: the showed reference, the self-referencing . entry, and then a .. entry in each of its subfolders;
  • owner user name;
  • group name;
  • size;
  • last modification timestamp;
  • entity name.

File names containing spaces enclosed in quotes

By default, file and directory names that contain spaces are displayed surrounded by single quotes. To change this behavior use the -N or --quoting-style=literal options. Alternatively, set the QUOTING_STYLE environment variable to literal. [1]

cat

cat is a standard Unix utility that concatenates files to standard output.

  • Because cat is not built into the shell, on many occasions you may find it more convenient to use a redirection, for example in scripts, or if you care a lot about performance. In fact < file does the same as cat file.
  • cat can work with multiple lines:
$ cat << EOF >> path/file
first line
...
last line
EOF

Alternatively, using printf:

$ printf '%s\n' 'first line' ... 'last line'
  • If you need to list file lines in reverse order, there is a coreutil command called tac (cat reversed).

less

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: less is a complex beast, and this section should explain some of the basic less commands (Discuss in Talk:Core utilities#)
less is a terminal pager program used to view the contents of a text file one screen at a time. Whilst similar to other pagers such as more and the deprecated pg, less offers a more advanced interface and complete feature-set.

See List of applications#Terminal pagers for alternatives.

Vim as alternative pager

Vim includes a script to view the content of text files, compressed files, binaries and directories. Add the following line to your shell configuration file to use it as a pager:

~/.bashrc
alias less='/usr/share/vim/vim80/macros/less.sh'

There is also an alternative to the less.sh macro, which may work as the PAGER environment variable. Install vimpager 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.

mkdir

mkdir makes directories.

To create a directory and its whole hierarchy, the -p switch is used, otherwise an error is printed.

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 just want a temporary directory, a better alternative may be mktemp: mktemp -d

mv

mv moves and renames files and directories.

Note: "Security aliases" are dangerous because you get used to them, resulting in potential data loss when you use another system / user that doesn't have these aliases.

To limit potential damage caused by the command, use an alias:

alias mv='mv -iv'

This alias asks for confirmation before overwriting any existing files and lists the operations in progress.

rm

rm removes files or directories.

Note: "Security aliases" are dangerous because you get used to them, resulting in potential data loss when you use another system / user that doesn't have these aliases.

To limit potential damage caused by the command, use an alias:

alias rm='rm -Iv --one-file-system'

This alias asks confirmation to delete three or more files, lists the operations in progress, does not involve more than one file systems. Substitute -I with -i if you prefer to confirm even for one file.

Zsh users may want to prefix noglob to avoid implicit expansions.

To remove directories believed to be empty, use rmdir as it fails if there are files inside the target.

chmod

See File permissions and attributes#Changing permissions.

chown

See File permissions and attributes#Changing ownership.

find

find is part of the findutils package, which belongs to the base package group.

Tip: fd is a simple, fast and user-friendly alternative to find that provides more sensible defaults (e.g. ignores hidden files, directories and .gitignore'd files, fd PATTERN instead of find -iname '*PATTERN*'). It features colorized output (similar to ls), Unicode awareness, regular expressions and more.

One would probably expect a find command to take as argument a file name and search the filesystem for files matching that name. For a program that does exactly that see #locate below.

Instead, find takes a set of directories and matches each file under them against a set of expressions. This design allows for some very powerful "one-liners" that would not be possible using the "intuitive" design described above. See GregsWiki:UsingFind for usage details.

locate

Install the mlocate package. The package contains an updatedb.timer unit, which invokes a database update each day. The timer is enabled right after installation, start it manually if you want to use it before reboot. You can also manually run updatedb as root at any time. By default, paths such as /media and /mnt are ignored, so locate may not discover files on external devices. See updatedb(8) for details.

The locate command is a common Unix tool for quickly finding files by name. It offers speed improvements over the find tool by searching a pre-constructed database file, rather than the filesystem directly. The downside of this approach is that changes made since the construction of the database file cannot be detected by locate.

Before locate can be used, the database will need to be created. To do this, execute updatedb as root.

See also How locate works and rewrite it in one minute.

Text streams

grep

grep is a command line text search utility originally written for Unix. The grep command searches files or standard input for lines matching a given regular expression, and prints these lines to standard output.

  • Remember that grep handles files, so a construct like cat file | grep pattern is replaceable with grep pattern file
  • There are grep alternatives optimized for VCS source code, such as ripgrep, the_silver_searcher, and ack.
  • To include file line numbers in the output, use the -n option.
  • grep can also be used for hexadecimal search in a binary file, to look for let say the A1 F2 sequence in a file, the command line is:
    $ LANG=C grep --text --perl-regexp "\xA1\xF2" /path/to/file
Note: Some commands send their output to stderr(3), and grep has no apparent effect. In this case, redirect stderr to stdout with command 2>&1 | grep args or (for Bash 4) command |& grep args. See also I/O Redirection.

For color support, see Color output in console#grep.

See grep(1) for more details.

sed

sed is stream editor for filtering and transforming text.

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

Tip: More powerful alternatives are awk and the Perl language.

awk

AWK is a pattern scanning and processing language. There are multiple implementations:

  • gawk — GNU version of awk, see gawk(1).
https://www.gnu.org/software/gawk/ || gawk (part of base)
  • nawk — The one, true implementation of AWK, see nawk(1).
https://www.cs.princeton.edu/~bwk/btl.mirror/ || nawk
  • mawk — A very fast AWK implementation.
http://invisible-island.net/mawk/ || mawkAUR
  • BusyBox also includes an AWK implementation.

pv

Tango-edit-cut.pngThis section is being considered for removal.Tango-edit-cut.png

Reason: Not part of coreutils, util-linux, or base. Is it a "core utility"? (Discuss in Talk:Core utilities#)

You can use pv to monitor the progress of data through a pipeline, for example:

# dd if=/source/filestream | pv -monitor_options -s size_of_file | dd of=/destination/filestream

In most cases pv functions as a drop-in replacement for cat.

System administration

Command Description Manual page Example
mount Mount a partition mount(8) mount /dev/sdc1 /media/usb
df -h Show remaining space on all partitions df(1)
ps -A Show all running processes ps(1)
killall Kill all running instances of a process killall(1)
ss -at Display a list of open TCP sockets ss(8)

sudo

See Sudo.

which

which shows the full path of shell commands. In the following example the full path of ssh is used as an argument for journalctl:

# journalctl $(which sshd)

lsblk

lsblk(8) will show all available block devices along with their partitioning schemes, for example:

$ lsblk -f
NAME   FSTYPE   LABEL       UUID                                 MOUNTPOINT
sda
├─sda1 vfat                 C4DA-2C4D                            /boot
├─sda2 swap                 5b1564b2-2e2c-452c-bcfa-d1f572ae99f2 [SWAP]
└─sda3 ext4                 56adc99b-a61e-46af-aab7-a6d07e504652 /

The beginning of the device name specifies the type of block device. Most modern storage devices (e.g. hard disks, SSDs and USB flash drives) are recognised as SCSI disks (sd). The type is followed by a lower-case letter starting from a for the first device (sda), b for the second device (sdb), and so on. Existing partitions on each device will be listed with a number starting from 1 for the first partition (sda1), 2 for the second (sda2), and so on. In the example above, only one device is available (sda), and that device has three partitions (sda1 to sda3), each with a different file system.

Other common block device types include for example mmcblk for memory cards and nvme for NVMe devices. Unknown types can be searched in the kernel documentation.

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.

Note: The ip utility is provided by the iproute2 package, which is included in the base group.
Object Purpose Manual page
ip addr protocol address management ip-address(8)
ip addrlabel protocol address label management ip-addrlabel(8)
ip l2tp tunnel Ethernet over IP (L2TPv3) ip-l2tp(8)
ip link network device configuration ip-link(8)
ip maddr multicast addresses management ip-maddress(8)
ip monitor watch for netlink messages ip-monitor(8)
ip mroute multicast routing cache management ip-mroute(8)
ip mrule rule in multicast routing policy db
ip neigh neighbour/ARP tables management ip-neighbour(8)
ip netns process network namespace management ip-netns(8)
ip ntable neighbour table configuration ip-ntable(8)
ip route routing table management ip-route(8)
ip rule routing policy database management ip-rule(8)
ip tcp_metrics management for TCP Metrics ip-tcp_metrics(8)
ip tunnel tunnel configuration ip-tunnel(8)
ip tuntap manage TUN/TAP devices
ip xfrm manage IPsec policies ip-xfrm(8)

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. For advanced usage see the iproute2 documentation.

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 is deprecated in Arch Linux; use ip instead.

ss

ss is a utility to investigate network ports and is part of the iproute2 package in the base group. It has a similar functionality to the deprecated netstat utility.

Common usage includes:

Display all TCP Sockets with service names:

$ ss -at

Display all TCP Sockets with port numbers:

$ ss -atn

Display all UDP Sockets:

$ ss -au

For more information see ss(8) or ss.html from the iproute2 package.

Miscellaneous

Command Description Manual page Example
strings Show printable characters in binary files strings(1) strings /usr/bin/free

dd

dd is a utility for Unix and Unix-like operating systems whose primary purpose is to convert and copy a file.

Similarly to cp, by default dd makes a bit-to-bit copy of the file, but with lower-level I/O flow control features.

Some notable applications of dd are:

  • Binary file patching: let say one wants to replace offset 0x123AB of a file with the FF C0 14 hexadecimal sequence, this can be done with the command line:
    # printf '\xff\xc0\x14' | dd seek=$((0x123AB)) conv=notrunc bs=1 of=/path/to/file

For more information see dd(1) or the full documentation.

Tip: By default, dd outputs nothing until the task has finished. To monitor the progress of the operation, add the status=progress option to the command.
Warning: One should be extremely cautious using dd, as with any command of this kind it can destroy data irreversibly.

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 iconv(1) for more details.

Convert a file in place

Tip: You can use recode instead of iconv if you do not want to touch the mtime.

Unlike sed, iconv does not provide an option to convert a file in place. However, sponge from the moreutils package can help:

$ iconv -f WINDOWS-1251 -t UTF-8 foobar.txt | sponge foobar.txt

See sponge(1) for details.

od

The od (octal dump) command is useful for visualizing data that is not in a human-readable format, like the executable code of a program, or the contents of an unformatted device. See the manual for more information.

seq

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

tar

As an early Unix archiving format, .tar files—known as "tarballs"—are widely used for packaging in Unix-like operating systems. Both pacman and AUR packages are compressed tarballs, and Arch uses GNU's tar program by default.

For .tar archives, tar by default will extract the file according to its extension:

$ tar xvf file.EXTENSION

Forcing a given format:

File Type Extraction Command
file.tar tar xvf file.tar
file.tgz tar xvzf file.tgz
file.tar.gz tar xvzf file.tar.gz
file.tar.bz bzip -cd file.bz | tar xvf -
file.tar.bz2 tar xvjf file.tar.bz2
bzip2 -cd file.bz2 | tar xvf -
file.tar.xz tar xvJf file.tar.xz
xz -cd file.xz | tar xvf -
file.tar.zst tar -I zstd xvf file.tar.zst

The construction of some of these tar arguments may be considered legacy, but they are still useful when performing specific operations. See tar(1) for details.

Note: Although GNU's tar is installed as the default tar program, official Arch Linux projects like pacman and mkinitcpio use bsdtar from the libarchive package.

wipefs

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Why would you want to erase magic strings? (Discuss in Talk:Core utilities#)

wipefs can list or erase file system, RAID or partition-table signatures (magic strings) from the specified device. It does not erase the file systems themselves nor any other data from the device.

See wipefs(8) for more information.

For example, to erase all signatures from the device /dev/sdb and create a signature backup ~/wipefs-sdb-offset.bak file for each signature:

# wipefs --all --backup /dev/sdb

See also