Core utilities

Related articles

• Command-line shell
• General recommendations
• GNU
• sudo
• cron
• man page
• Securely wipe disk#shred
• File permissions and attributes
• Color output in console
• Archiving and compression
• chmod
• chown

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.

The -l option (long format) can be used to display file type, permissions, owner user & group, size, modification timestamp and more, see the info document.

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.

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.

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 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

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 -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.

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.

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.

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 || cwdiff^AUR, cwdiff-git^AUR

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.

• 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.

Tip: There are grep alternatives optimized for VCS source code, such as ripgrep, the_silver_searcher, and ack. There also is mgrep^AUR, a multiline grep.

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/ || mawk^AUR

• 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 shows all available block devices along with their partitioning schemes.

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 was used in older Linux systems. It is deprecated in Arch Linux; use ip instead.

ss

See Network configuration#Investigate sockets.

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.

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.

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

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.

See also Archiving and compression.

wipefs

wipefs can list or erase file system, RAID or partition-table signatures (magic strings) from the specified device.

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