Core utilities: Difference between revisions
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{{Related articles start}} | {{Related articles start}} | ||
{{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 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. | ||
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 == | ||
{| class="wikitable" | |||
! Command | |||
{| class=wikitable | ! Description | ||
! Manual page | |||
! Example | |||
|- | |- | ||
| shell built- | | 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 | ||
| | |} | ||
|- | |||
| | === ls === | ||
|- | |||
| GNU {{Pkg|diffutils}} | [[Wikipedia:ls|ls]] lists directory contents. | ||
| | |||
| GNU {{ | 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. | ||
==== 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. | |||
{{Remove|Unnecessary detail found in man pages}} | |||
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| | |||
$ cat << EOF >> ''path/file'' | |||
''first line'' | |||
... | |||
''last line'' | |||
EOF | |||
}} | |||
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 ==== | |||
{{Move|Vim|Discusses a ''vim'' specifity}} | |||
[[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 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. | |||
=== chmod === | |||
See [[File permissions and attributes#Changing permissions]]. | |||
=== chown === | |||
See [[File permissions and attributes#Changing ownership]]. | |||
=== 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 == | |||
Shell [[Wikipedia:Pipeline (Unix)|pipelines]] operate on stdout by default. To operate on {{man|3|stderr}} you can redirect ''stderr'' to ''stdout'' with {{ic|''command'' 2>&1 {{!}} ''othercommand''}} or, for Bash 4, {{ic|''command'' {{!}}& ''othercommand''}}. See also [http://www.tldp.org/LDP/abs/html/io-redirection.html I/O Redirection]. | |||
=== 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|grep ''pattern'' < ''file''}} is replaceable with {{ic|grep ''pattern'' ''file''}}. | |||
* 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 | ||
| 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 / | |||
}} | |||
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]]. | |||
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]. | |||
=== 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. | |||
{{Note|The ''ip'' utility is provided by the {{Pkg|iproute2}} package, which is included in the {{Grp|base}} group.}} | |||
{| class=wikitable | {| class="wikitable" | ||
! | ! Object !! Purpose !! Manual page | ||
|- | |||
| ip addr || protocol address management || {{man|8|ip-address}} | |||
|- | |- | ||
| | | 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 {{ | 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 was used in older Linux systems. It 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. | |||
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 {{man|1|iconv}} for more details. | |||
==== Convert a file in place ==== | |||
{{Tip|You can use {{pkg|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, {{ic|sponge}} from the {{pkg|moreutils}} package can help: | |||
$ iconv -f WINDOWS-1251 -t UTF-8 ''foobar''.txt | sponge ''foobar''.txt | |||
See {{man|1|sponge}} for details. | |||
=== 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 === | |||
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.}} | |||
See also [[Archiving and compression]]. | |||
=== wipefs === | |||
{{Expansion|Why would you want to erase magic strings?}} | |||
''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. | |||
See {{man|8|wipefs}} for more information. | |||
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: | |||
# wipefs --all --backup /dev/sdb | |||
== See also == | == See also == | ||
* [https://www.gnu.org/software/coreutils/manual/coreutils.html GNU Coreutils documentation] | * [http://pubs.opengroup.org/onlinepubs/9699919799/idx/utilities.html POSIX Utilities] | ||
* [http:// | * [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] |
Revision as of 13:04, 23 August 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, 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.
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 the ls
Info manual (online version) 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 is available as the exa package.
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;
- the first character is the entry type, see
- 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 ascat 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
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.
mktemp -d
mv
mv moves and renames files and directories.
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.
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.
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.
diff
diff compares files line by line. Its output can be saved to a so-called patch file, which can be applied using the patch(1) utility. The default Arch Linux diff is from the GNU 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 comm(1).
When comparing text files a word per word diff is often more desirable:
- git's
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.
- GNU wdiff — A wordwise implementation of GNU diff; does not support colors.
- cwdiff — A GNU wdiff wrapper that colorizes the output.
Text streams
Shell pipelines operate on stdout by default. To operate on stderr(3) you can redirect stderr to stdout with command 2>&1 | othercommand
or, for Bash 4, command |& othercommand
. See also I/O Redirection.
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
grep pattern < file
is replaceable withgrep pattern file
. - 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
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.
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).
- mawk — A very fast AWK implementation.
- BusyBox also includes an AWK implementation.
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.
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.
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 theFF 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.
status=progress
option to the command.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
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.
See also Archiving and compression.
wipefs
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
- POSIX Utilities
- GNU Coreutils online documentation
- A sampling of coreutils on Reddit , part 2 , part 3 - Overview of commands in coreutils
- Learn the DD command