Difference between revisions of "Core utilities"

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{{Related|Command-line shell}}
 
{{Related|Command-line shell}}
 
{{Related|General recommendations}}
 
{{Related|General recommendations}}
{{Related|GNU}}
 
{{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}}
 
{{Related|chmod}}
 
{{Related|chown}}
 
 
{{Related articles end}}
 
{{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.
+
''Core utilities'' are the basic, fundamental tools of a [[GNU]]/[[Linux]] system. On Arch Linux they are found in the {{Grp|base}} group. This article provides an incomplete overview of them, links their documentation and describes useful alternatives. Most core utilities are traditional [[Wikipedia:Unix|Unix]] tools (see [[Heirloom]]) and many were standardized by [[Wikipedia:POSIX|POSIX]] but have been developed further to provide more features.
  
 
Most command-line interfaces are documented in [[man page]]s, utilities by the [[GNU Project]] are documented in [[Info manual]]s, some [[shell]]s provide a {{ic|help}} command for [[shell]] builtin commands. Additionally most commands print their usage when run with the {{ic|--help}} flag.
 
Most command-line interfaces are documented in [[man page]]s, utilities by the [[GNU Project]] are documented in [[Info manual]]s, some [[shell]]s provide a {{ic|help}} command for [[shell]] builtin commands. Additionally most commands print their usage when run with the {{ic|--help}} flag.
  
== File management ==
+
== Essentials ==
  
{| class="wikitable"
+
The following table lists important commands, Arch Linux users should be familiar with. See also {{man|1|intro}}.
! Command
+
 
! Description
+
{| class=wikitable
! Manual page
+
! Package !! Command !! Description !! Documentation !! Alternatives
! Example
+
|-
 +
| shell built-ins || cd || change directory || {{man|1p|cd}}
 +
|-
 +
|rowspan=12| GNU {{Pkg|coreutils}}
 +
| ls || list directory || {{man|1|ls}}, [https://www.gnu.org/software/coreutils/manual/html_node/ls-invocation.html info] || {{Pkg|exa}}, {{Pkg|tree}}
 +
|-
 +
| cat || concatenate files to stdout || {{man|1|cat}}, [https://www.gnu.org/software/coreutils/manual/html_node/cat-invocation.html info] || {{man|1|tac}}
 +
|-
 +
| mkdir || make directory || {{man|1|mkdir}}, [https://www.gnu.org/software/coreutils/manual/html_node/mkdir-invocation.html info]
 +
|-
 +
| rmdir || remove empty directory || {{man|1|rmdir}}, [https://www.gnu.org/software/coreutils/manual/html_node/rmdir-invocation.html info]
 +
|-
 +
| rm || remove files or directories || {{man|1|rm}}, [https://www.gnu.org/software/coreutils/manual/html_node/rm-invocation.html info] || [[shred]]
 +
|-
 +
| cp || copy files or directories || {{man|1|cp}}, [https://www.gnu.org/software/coreutils/manual/html_node/cp-invocation.html info]
 +
|-
 +
| mv || move files or directories || {{man|1|mv}}, [https://www.gnu.org/software/coreutils/manual/html_node/mv-invocation.html info]
 +
|-
 +
| ln || make hard or symbolic links || {{man|1|ln}}, [https://www.gnu.org/software/coreutils/manual/html_node/ln-invocation.html info]
 
|-
 
|-
| cd
+
| [[chown]] || change file owner and group || {{man|1|chown}}, [https://www.gnu.org/software/coreutils/manual/html_node/chown-invocation.html info]
| Change directory (shell built-in command)
 
| {{man|1p|cd}}
 
| cd /etc/pacman.d
 
 
|-
 
|-
| mkdir
+
| [[chmod]] || change file permissions || {{man|1|chmod}}, [https://www.gnu.org/software/coreutils/manual/html_node/chmod-invocation.html info]
| Create a directory
 
| {{man|1|mkdir}}
 
| mkdir ~/newfolder
 
 
|-
 
|-
| rmdir
+
| [[dd]] || convert and copy a file || {{man|1|dd}}, [https://www.gnu.org/software/coreutils/manual/html_node/dd-invocation.html info]
| Remove empty directory
 
| {{man|1|rmdir}}
 
| rmdir ~/emptyfolder
 
 
|-
 
|-
| rm
+
| df || report file system disk space usage || {{man|1|df}}, [https://www.gnu.org/software/coreutils/manual/html_node/df-invocation.html info]
| Remove a file
 
| {{man|1|rm}}
 
| rm ~/file.txt
 
 
|-
 
|-
| rm -r
+
| GNU {{Pkg|tar}} || [[tar]] || tar archiver || {{man|1|tar}}, [https://www.gnu.org/software/tar/manual/html_chapter/index.html info] || [[archive]]rs
| Remove directory and contents
 
|
 
| rm -r ~/.cache
 
 
|-
 
|-
| ls
+
| GNU {{Pkg|less}} || less || terminal pager || {{man|1|less}} || [[terminal pager]]s
| List files
 
| {{man|1|ls}}
 
| ls *.mkv
 
 
|-
 
|-
| ls -a
+
| GNU {{Pkg|findutils}} || find || search files or directories || {{man|1|find}}, [https://www.gnu.org/software/findutils/manual/html_node/find_html/index.html info], [[GregsWiki:UsingFind|GregsWiki]] || [[#find alternatives]]
| List hidden files
 
|
 
| ls -a /home/archie
 
 
|-
 
|-
| ls -al
+
| GNU {{Pkg|diffutils}} || diff || compare files line by line || {{man|1|diff}}, [https://www.gnu.org/software/diffutils/manual/html_node/Invoking-diff.html info] || [[#diff alternatives]]
| List hidden files and file properties
 
|
 
|
 
 
|-
 
|-
| mv
+
| GNU {{Pkg|grep}} || grep || print lines matching a pattern || {{man|1|grep}}, [https://www.gnu.org/software/grep/manual/html_node/index.html info] || [[#grep alternatives]]
| Move a file
 
| {{man|1|mv}}
 
| mv ~/compressed.zip ~/archive/compressed2.zip
 
 
|-
 
|-
| cp
+
| GNU {{Pkg|sed}} || sed || stream editor || {{man|1|sed}}, [https://www.gnu.org/software/sed/manual/html_node/index.html info], [http://sed.sourceforge.net/sed1line.txt one-liners]
| Copy a file
 
| {{man|1|cp}}
 
| cp ~/.bashrc ~/.bashrc.bak
 
 
|-
 
|-
| chmod +x
+
| GNU {{Pkg|gawk}} || awk || pattern scanning and processing language || {{man|1|gawk}}, [https://www.gnu.org/software/gawk/manual/html_node/index.html info] || {{Pkg|nawk}}, {{AUR|mawk}}
| Make a file [[executable]]
 
| {{man|1|chmod}}
 
| chmod +x ~/.local/bin/myscript.sh
 
 
|-
 
|-
| cat
+
|rowspan=5| {{Pkg|util-linux}}
| Show file contents
+
| [[lsblk]] || list block devices || {{man|8|lsblk}}
| {{man|1|cat}}
 
| cat /etc/hostname
 
 
|-
 
|-
| find
+
| [[mount]] || mount a filesystem || {{man|8|mount}}
| Search for a file
 
| {{man|1|find}}
 
| find ~ -name myfile
 
|}
 
 
 
=== ls ===
 
 
 
[[Wikipedia:ls|ls]] lists directory contents.
 
 
 
See the {{ic|ls}} [[Info manual]] ([https://www.gnu.org/software/coreutils/manual/html_node/ls-invocation.html#ls-invocation online version]) 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. ''exa'' is available as the {{Pkg|exa}} package.
 
 
 
The {{ic|-l}} option (long format) can be used to display file type, [[permissions]], owner [[user]] & [[group]], size, modification timestamp and more, see the [https://www.gnu.org/software/coreutils/manual/html_node/What-information-is-listed.html#index-long-ls-format info document].
 
 
 
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.
 
 
 
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.
 
 
 
=== 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 does not 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.
 
 
 
{{Note|"Security aliases" are dangerous because you get used to them, resulting in potential data loss when you use another system / user that does not 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 {{ic|-I}} with {{ic|-i}} if you prefer to confirm even for one file.
 
 
 
Zsh users may want to prefix {{ic|noglob}} to avoid implicit expansions.
 
 
 
To remove directories believed to be empty, use ''rmdir'' as it fails if there are files inside the target.
 
 
 
=== find ===
 
 
 
''find'' is part of the {{Pkg|findutils}} package, which belongs to the {{Grp|base}} package group.
 
 
 
{{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.}}
 
 
 
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 {{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.
 
 
 
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''.
 
 
 
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].
 
 
 
=== diff ===
 
 
 
''diff'' compares files line by line. Its output can be saved to a so-called patch file, which can be applied using the {{man|1|patch}} utility. The default Arch Linux ''diff'' is from the GNU {{Pkg|diffutils}}, which also provides ''cmp'' to compare files byte by byte.
 
 
 
A similar command, which lets you compare two sorted files line by line is ''comm'', see {{man|1|comm}}.
 
 
 
When comparing text files a word per word diff is often more desirable:
 
 
 
* [[git]]'s {{ic|git diff}} can do a word diff with {{ic|--color-words}}, using {{ic|--no-index}} it can also be used for files outside of Git working trees.
 
* {{App|dwdiff|A word diff front-end for the diff program; supports colors.|https://os.ghalkes.nl/dwdiff.html|{{Pkg|dwdiff}}}}
 
* {{App|GNU wdiff|A wordwise implementation of GNU diff; does not support colors.|https://www.gnu.org/software/wdiff/|{{Pkg|wdiff}}}}
 
* {{App|cwdiff|A GNU wdiff wrapper that colorizes the output.|https://github.com/junghans/cwdiff|{{AUR|cwdiff}}, {{AUR|cwdiff-git}}}}
 
 
 
== 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.
 
 
 
* 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''}}
 
 
 
For color support, see [[Color output in console#grep]].
 
 
 
See {{man|1|grep}} for more details.
 
 
 
{{Tip|There are ''grep'' alternatives optimized for VCS source code, such as {{Pkg|ripgrep}}, {{Pkg|the_silver_searcher}}, and {{Pkg|ack}}. There also is {{AUR|mgrep}}, a multiline grep.}}
 
 
 
=== 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.
 
 
 
== System administration ==
 
 
 
{| class="wikitable"
 
! Command
 
! Description
 
! Manual page
 
! Example
 
 
|-
 
|-
| mount
+
| [[umount]] || unmount a filesystem || {{man|8|umount}}
| Mount a partition
 
| {{man|8|mount}}
 
| mount /dev/sdc1 /media/usb
 
 
|-
 
|-
| df -h
+
| [[su]] || substitute user || {{man|1|su}} || [[sudo]]
| Show remaining space on all partitions
 
| {{man|1|df}}
 
|
 
 
|-
 
|-
| ps -A
+
| kill || terminate a process || {{man|1|kill}} || {{man|1|pkill}}, {{man|1|killall}}
| Show all running processes
 
| {{man|1|ps}}
 
|
 
 
|-
 
|-
| killall
+
|rowspan=2| {{Pkg|procps-ng}}
| Kill all running instances of a process
+
| ps || show information about processes || {{man|1|ps}} ||rowspan=2| {{man|1|top}}, {{Pkg|htop}}
| {{man|1|killall}}
 
|
 
 
|-
 
|-
| ss -at
+
| free || display amount of free and used memory || {{man|1|free}}
| Display a list of open TCP sockets
 
| {{man|8|ss}}
 
|
 
 
|}
 
|}
  
=== sudo ===
+
=== Preventing data loss ===
 
 
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}}:
+
rm, mv, cp and shell redirections happily delete or overwrite files without asking. rm, mv and cp all support the {{ic|-i}} flag to prompt the user before every removal / overwrite. Some users like to enable the {{ic|-i}} flag by default using [[alias]]es. Such shell settings are however dangerous because you get used to them, resulting in potential data loss when you use another system or user that does not have them. The best way to prevent data loss is to do [[backup]]s.
  
# journalctl $(which sshd)
+
== Nonessentials ==
  
=== lsblk ===
+
This table lists core utilities that often come in handy.
  
[[lsblk]] shows all available [[Wikipedia:Device file#Block devices|block devices]] along with their partitioning schemes.
+
{| class=wikitable
 
+
! Package !! Command !! Description !! Documentation !! Alternatives
=== ip ===
 
 
 
{{Remove|Duplicates [[Network configuration#Network management]] and {{man|8|ip}}. Table is unnecessary, documentation link is outdated.|section=Rewrite}}
 
 
 
[[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.
 
 
 
{{Note|The ''ip'' utility is provided by the {{Pkg|iproute2}} package, which is included in the {{Grp|base}} group.}}
 
 
 
{| class="wikitable"
 
! Object !! Purpose !! Manual page
 
 
|-
 
|-
| ip addr || protocol address management || {{man|8|ip-address}}
+
|rowspan=3| shell built-ins
 +
| alias || define or display aliases || {{man|1|alias}}
 
|-
 
|-
| ip addrlabel || protocol address label management || {{man|8|ip-addrlabel}}
+
| type || print the type of a command || {{man|1|type}} || {{man|1|which}}
 
|-
 
|-
| ip l2tp || tunnel Ethernet over IP (L2TPv3) || {{man|8|ip-l2tp}}
+
| time || time a command || {{man|1|time}}
 
|-
 
|-
| ip link || network device configuration || {{man|8|ip-link}}
+
|rowspan=9| GNU {{Pkg|coreutils}}
 +
| tee || read stdin and write to stdout and files || {{man|1|tee}}, [https://www.gnu.org/software/coreutils/manual/html_node/tee-invocation.html info]
 
|-
 
|-
| ip maddr || multicast addresses management || {{man|8|ip-maddress}}
+
| mktemp || make a temporary file or directory || {{man|1|mktemp}}, [https://www.gnu.org/software/coreutils/manual/html_node/mktemp-invocation.html info]
 
|-
 
|-
| ip monitor || watch for netlink messages || {{man|8|ip-monitor}}
+
| od || dump files in octal and other formats || {{man|1|od}}, [https://www.gnu.org/software/coreutils/manual/html_node/od-invocation.html info] || {{man|1|hexdump}}, [[vim]]'s {{man|1|xxd}}
 
|-
 
|-
| ip mroute || multicast routing cache management || {{man|8|ip-mroute}}
+
| sort || sort lines || {{man|1|sort}}, [https://www.gnu.org/software/coreutils/manual/html_node/sort-invocation.html info]
 
|-
 
|-
| ip mrule || rule in multicast routing policy db ||
+
| uniq || report or omit repeated lines || {{man|1|uniq}}, [https://www.gnu.org/software/coreutils/manual/html_node/uniq-invocation.html info]
 
|-
 
|-
| ip neigh || neighbour/ARP tables management || {{man|8|ip-neighbour}}
+
| comm || compare two sorted files line by line || {{man|1|comm}}, [https://www.gnu.org/software/coreutils/manual/html_node/comm-invocation.html info]
 
|-
 
|-
| ip netns || process network namespace management || {{man|8|ip-netns}}
+
| head || output the first part of files || {{man|1|head}}, [https://www.gnu.org/software/coreutils/manual/html_node/head-invocation.html info]
 
|-
 
|-
| ip ntable || neighbour table configuration || {{man|8|ip-ntable}}
+
| tail || output the last part of files, or follow files || {{man|1|tail}}, [https://www.gnu.org/software/coreutils/manual/html_node/tail-invocation.html info]
 
|-
 
|-
| ip route || routing table management || {{man|8|ip-route}}
+
| wc || print newline, word and byte count || {{man|1|wc}}, [https://www.gnu.org/software/coreutils/manual/html_node/wc-invocation.html info]
 
|-
 
|-
| ip rule || routing policy database management || {{man|8|ip-rule}}
+
| GNU {{Pkg|binutils}} || strings || print printable characters in binary files || {{man|1|strings}}, [https://sourceware.org/binutils/docs/binutils/strings.html info]
 
|-
 
|-
| ip tcp_metrics || management for TCP Metrics || {{man|8|ip-tcp_metrics}}
+
| GNU {{Pkg|glibc}} || iconv || convert character encodings || {{man|1|iconv}} || {{Pkg|recode}}
 
|-
 
|-
| ip tunnel || tunnel configuration || {{man|8|ip-tunnel}}
+
| {{Pkg|file}} || file || guess file type || {{man|1|file}}
|-
 
| 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 {{Pkg|moreutils}} package provides useful tools like {{man|1|sponge}} that are missing from the GNU coreutils.
  
The [[Network configuration]] article shows how the ''ip'' command is used in practice for various common tasks.
+
== Alternatives ==
  
{{Note|You might be familiar with the [[Wikipedia:ifconfig|ifconfig]] command, which was used in older Linux systems. It is deprecated in Arch Linux; use ''ip'' instead. }}
+
Alternatives to the core utilities in the {{Grp|base}} group are [[BusyBox]], the [[Heirloom|Heirloom Toolchest]], {{Pkg|9base}}, {{AUR|sbase-git}} and {{AUR|ubase-git}}.
  
=== ss ===
+
=== find alternatives ===
  
See [[Network configuration#Investigate sockets]].
+
* {{App|fd|Simple, fast and user-friendly alternative to find. Ignores hidden and {{ic|.gitignore}}'d files by default.|https://github.com/sharkdp/fd|{{Pkg|fd}}}}
  
== Miscellaneous ==
+
==== locate ====
  
{| class="wikitable"
+
[[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.
! Command
 
! Description
 
! Manual page
 
! Example
 
|-
 
| strings
 
| Show printable characters in binary files
 
| {{man|1|strings}}
 
| strings /usr/bin/free
 
|}
 
  
=== dd ===
+
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''.
  
[[dd]] is a utility for Unix and Unix-like operating systems whose primary purpose is to convert and copy a file.
+
Before ''locate'' can be used, the database will need to be created. To do this, execute {{ic|updatedb}} as root.
  
=== iconv ===
+
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].
  
''iconv'' converts the encoding of characters from one codeset to another.
+
=== diff alternatives ===
  
The following command will convert the file {{ic|''foo''}} from ISO-8859-15 to UTF-8, saving it to {{ic|''foo''.utf}}:
+
While {{Pkg|diffutils}} does not provide a word-wise diff, several other programs do:
  
$ iconv -f ISO-8859-15 -t UTF-8 ''foo'' > ''foo''.utf
+
* [[git]] diff can do a word diff with {{ic|--color-words}}, using {{ic|--no-index}} it can also be used for files outside of Git working trees.
 
+
* {{App|dwdiff|A word diff front-end for the diff program; supports colors.|https://os.ghalkes.nl/dwdiff.html|{{Pkg|dwdiff}}}}
See {{man|1|iconv}} for more details.
+
* {{App|GNU wdiff|A wordwise implementation of GNU diff; does not support colors.|https://www.gnu.org/software/wdiff/|{{Pkg|wdiff}}}}
 
+
* {{App|cwdiff|A GNU wdiff wrapper that colorizes the output.|https://github.com/junghans/cwdiff|{{AUR|cwdiff}}, {{AUR|cwdiff-git}}}}
{{Tip|You can use {{pkg|recode}} instead of iconv if you do not want to touch the mtime.}}
 
 
 
=== od ===
 
 
 
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.
 
 
 
=== 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:Seq (Unix)|Wikipedia]].
 
 
 
=== tar ===
 
 
 
{{Remove|Duplicates [[Archiving and compression#Archiving only]], table isn't needed, tar can autodetect the format.|section=Rewrite}}
 
 
 
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.
 
 
 
For ''.tar'' archives, ''tar'' by default will extract the file according to its extension:
 
 
 
$ tar xvf ''file.EXTENSION''
 
 
 
Forcing a given format:
 
 
 
{| 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}}
 
|}
 
 
 
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.
 
  
{{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.}}
+
=== grep alternatives ===
  
See also [[Archiving and compression]].
+
The following three tools aim to replace grep for code search. They do recursive search by default, skip binary files and respect {{ic|.gitignore}}.
  
=== wipefs ===
+
* {{App|ack|A Perl-based grep replacement, aimed at programmers with large trees of heterogeneous source code.|https://beyondgrep.com/|{{Pkg|ack}}}}
 +
* {{App|ripgrep (rg)|A search tool that combines the usability of ag with the raw speed of grep.|https://github.com/BurntSushi/ripgrep|{{Pkg|ripgrep}}}}
 +
* {{App|The Silver Searcher (ag)|Code searching tool similar to Ack, but faster.|https://github.com/ggreer/the_silver_searcher|{{Pkg|the_silver_searcher}}}}
  
[[wipefs]] can list or erase [[file system]], [[RAID]] or [[partition|partition-table]] signatures (magic strings) from the specified device.
+
And then there is also {{AUR|mgrep}}, a multiline grep.
  
 
== See also ==
 
== See also ==
  
* [http://pubs.opengroup.org/onlinepubs/9699919799/idx/utilities.html POSIX Utilities]
+
* [https://www.gnu.org/software/coreutils/manual/coreutils.html GNU Coreutils documentation]
* [https://www.gnu.org/software/coreutils/manual/coreutils.html GNU Coreutils online documentation]
+
* [http://pubs.opengroup.org/onlinepubs/9699919799/idx/utilities.html POSIX utilities]
* [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]
 

Revision as of 17:09, 31 August 2018

Core utilities are the basic, fundamental tools of a GNU/Linux system. On Arch Linux they are found in the base group. This article provides an incomplete overview of them, links their documentation and describes useful alternatives. Most core utilities are traditional Unix tools (see Heirloom) and many were standardized by POSIX but have been developed further to provide more features.

Most command-line interfaces are documented in man pages, utilities by the GNU Project are documented in Info manuals, some shells provide a help command for shell builtin commands. Additionally most commands print their usage when run with the --help flag.

Essentials

The following table lists important commands, Arch Linux users should be familiar with. See also intro(1).

Package Command Description Documentation Alternatives
shell built-ins cd change directory cd(1p)
GNU coreutils ls list directory ls(1), info exa, tree
cat concatenate files to stdout cat(1), info tac(1)
mkdir make directory mkdir(1), info
rmdir remove empty directory rmdir(1), info
rm remove files or directories rm(1), info shred
cp copy files or directories cp(1), info
mv move files or directories mv(1), info
ln make hard or symbolic links ln(1), info
chown change file owner and group chown(1), info
chmod change file permissions chmod(1), info
dd convert and copy a file dd(1), info
df report file system disk space usage df(1), info
GNU tar tar tar archiver tar(1), info archivers
GNU less less terminal pager less(1) terminal pagers
GNU findutils find search files or directories find(1), info, GregsWiki #find alternatives
GNU diffutils diff compare files line by line diff(1), info #diff alternatives
GNU grep grep print lines matching a pattern grep(1), info #grep alternatives
GNU sed sed stream editor sed(1), info, one-liners
GNU gawk awk pattern scanning and processing language gawk(1), info nawk, mawkAUR
util-linux lsblk list block devices lsblk(8)
mount mount a filesystem mount(8)
umount unmount a filesystem umount(8)
su substitute user su(1) sudo
kill terminate a process kill(1) pkill(1), killall(1)
procps-ng ps show information about processes ps(1) top(1), htop
free display amount of free and used memory free(1)

Preventing data loss

rm, mv, cp and shell redirections happily delete or overwrite files without asking. rm, mv and cp all support the -i flag to prompt the user before every removal / overwrite. Some users like to enable the -i flag by default using aliases. Such shell settings are however dangerous because you get used to them, resulting in potential data loss when you use another system or user that does not have them. The best way to prevent data loss is to do backups.

Nonessentials

This table lists core utilities that often come in handy.

Package Command Description Documentation Alternatives
shell built-ins alias define or display aliases alias(1)
type print the type of a command type(1) which(1)
time time a command time(1)
GNU coreutils tee read stdin and write to stdout and files tee(1), info
mktemp make a temporary file or directory mktemp(1), info
od dump files in octal and other formats od(1), info hexdump(1), vim's xxd(1)
sort sort lines sort(1), info
uniq report or omit repeated lines uniq(1), info
comm compare two sorted files line by line comm(1), info
head output the first part of files head(1), info
tail output the last part of files, or follow files tail(1), info
wc print newline, word and byte count wc(1), info
GNU binutils strings print printable characters in binary files strings(1), info
GNU glibc iconv convert character encodings iconv(1) recode
file file guess file type file(1)

The moreutils package provides useful tools like sponge(1) that are missing from the GNU coreutils.

Alternatives

Alternatives to the core utilities in the base group are BusyBox, the Heirloom Toolchest, 9base, sbase-gitAUR and ubase-gitAUR.

find alternatives

  • fd — Simple, fast and user-friendly alternative to find. Ignores hidden and .gitignore'd files by default.
https://github.com/sharkdp/fd || fd

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.

diff alternatives

While diffutils does not provide a word-wise diff, several other programs do:

  • git diff can do a word diff with --color-words, using --no-index it can also be used for files outside of Git working trees.
  • dwdiff — A word diff front-end for the diff program; supports colors.
https://os.ghalkes.nl/dwdiff.html || dwdiff
  • GNU wdiff — A wordwise implementation of GNU diff; does not support colors.
https://www.gnu.org/software/wdiff/ || wdiff
  • cwdiff — A GNU wdiff wrapper that colorizes the output.
https://github.com/junghans/cwdiff || cwdiffAUR, cwdiff-gitAUR

grep alternatives

The following three tools aim to replace grep for code search. They do recursive search by default, skip binary files and respect .gitignore.

  • ack — A Perl-based grep replacement, aimed at programmers with large trees of heterogeneous source code.
https://beyondgrep.com/ || ack
  • ripgrep (rg) — A search tool that combines the usability of ag with the raw speed of grep.
https://github.com/BurntSushi/ripgrep || ripgrep
  • The Silver Searcher (ag) — Code searching tool similar to Ack, but faster.
https://github.com/ggreer/the_silver_searcher || the_silver_searcher

And then there is also mgrepAUR, a multiline grep.

See also