Basic Linux commands
last modified October 18, 2023
This article is an introduction to basic Linux commands on the shell. The tutorial presents a variety of basic Linux commands.
At the beginning, we assume an empty directory.
pwd command
We start in our home directory. The pwd command prints the current
working directory of the user.
$ pwd /home/jano/Documents/prog/linux/basic-commands
clear command
The clear command clears the terminal screen. Instead of this
command, we can use the Ctrl + L shortcut.
$ clear
whoami command
The whoami command prints the user name. This command is useful
when administrators are logged into multiple boxes.
$ whoami jano
hostname command
The hostname gives the name of the host. The hostname is the name
of the machine on then network.
$ hostname andromeda
date command
The date command prints the current local date.
$ date So 7. január 2023, 12:46:30 CET
The command prints the current local datetime.
$ date -u So 7. január 2023, 11:48:20 UTC
This command prints the current datetime in UTC.
$ date +%Y 2023 $ date +%F 2023-01-07
We print the date in the specified format.
$ date +%s 1673092327
This is the Unix time--the number of seconds that have elapsed since 00:00:00 UTC on 1 January 1970.
uptime command
$ uptime 04:39:18 up 45 min, 1 user, load average: 0.00, 0.01, 0.00
The uptime command tells how long the system is up.
man command
The man command gives us the manual for the command. There we can
find all the options for the command.
$ man date
cal command
The cal command gives us the calendar.
$ cal
Január 2023
Ne Po Ut St Št Pi So
1 2 3 4 5 6 7
8 9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31
$ cal -3
December 2022 Január 2023 Február 2023
Ne Po Ut St Št Pi So Ne Po Ut St Št Pi So Ne Po Ut St Št Pi So
1 2 3 1 2 3 4 5 6 7 1 2 3 4
4 5 6 7 8 9 10 8 9 10 11 12 13 14 5 6 7 8 9 10 11
11 12 13 14 15 16 17 15 16 17 18 19 20 21 12 13 14 15 16 17 18
18 19 20 21 22 23 24 22 23 24 25 26 27 28 19 20 21 22 23 24 25
25 26 27 28 29 30 31 29 30 31 26 27 28
With the -3 option, we get three months: the current, previous, and
next.
arch command
The arch command gives the machine architecture.
$ arch x86_64
$ arch --help
Usage: arch [OPTION]...
Print machine architecture.
--help display this help and exit
--version output version information and exit
...
Most commands have the --help option which gives a short help
information about a command.
uname command
The uname command gives system information. The -a
option lists all information.
$ uname Linux $ uname -a Linux andromeda 5.15.0-56-generic #62-Ubuntu SMP Tue Nov 22 19:54:14 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
who command
The who command lists users who are currently logged in.
$ who jano tty7 2023-01-07 10:04 (:0)
We have one logged user.
w command
$ w 12:56:24 up 2:55, 1 user, load average: 0,54, 0,50, 0,46 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT jano tty7 :0 10:04 2:55m 4:41 0.18s xfce4-session
The w command shows who is logeed in and what the users are doing.
echo command
The echo command prints a line of text to the terminal.
$ echo an old falcon an old falcon
We print a small message.
$ echo "an old falcon" | sed 's/falcon/wolf/' an old wolf
The sed command is used to transform text. We change the falcon
word to wolf in the text string.
$ echo $LANG $PWD en_US.UTF-8 /home/jano/Documents/prog/linux/basic-commands $ echo $SHELL $RANDOM $HOSTNAME /bin/bash 15604 andromeda
Here we print a couple of environment variables.
printf command
With the printf command, we can output formatted strings.
$ printf "%s is %d years old\n" Jane 17 Jane is 17 years old
We build a message with printf.
ping command
The ping command is used to check the network connectivity.
$ ping webcode.me PING webcode.me (46.101.248.126) 56(84) bytes of data. 64 bytes from 46.101.248.126 (46.101.248.126): icmp_seq=1 ttl=54 time=29.2 ms 64 bytes from 46.101.248.126 (46.101.248.126): icmp_seq=2 ttl=54 time=27.9 ms ...
The ping continuously sends requests until we terminate it with
Ctrl + C.
$ ping -c 4 webcode.me PING webcode.me (46.101.248.126) 56(84) bytes of data. 64 bytes from 46.101.248.126 (46.101.248.126): icmp_seq=1 ttl=54 time=32.1 ms 64 bytes from 46.101.248.126 (46.101.248.126): icmp_seq=2 ttl=54 time=34.6 ms 64 bytes from 46.101.248.126 (46.101.248.126): icmp_seq=3 ttl=54 time=33.4 ms 64 bytes from 46.101.248.126 (46.101.248.126): icmp_seq=4 ttl=54 time=37.9 ms --- webcode.me ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3004ms rtt min/avg/max/mdev = 32.100/34.497/37.876/2.145 ms
With the -c option, we specify the amout of requests sent.
df command
The df command reports the file system disk space usage.
$ df -h Filesystem Size Used Avail Use% Mounted on tmpfs 1,6G 3,5M 1,6G 1% /run /dev/nvme0n1p2 468G 194G 251G 44% / tmpfs 7,8G 14M 7,7G 1% /dev/shm tmpfs 5,0M 4,0K 5,0M 1% /run/lock tmpfs 7,8G 0 7,8G 0% /run/qemu /dev/nvme0n1p1 511M 5,3M 506M 2% /boot/efi tmpfs 1,6G 140K 1,6G 1% /run/user/1000
The -h option shows the size in human-readable format, that is in
in powers of 1024.
type command
There are two kinds of commands: shell builtins and external commands. The
type command can be used to gives the command type.
$ type echo who echo is a shell builtin who is hashed (/usr/bin/who)
We check echo and who commands.
history command
The history gives the history of the user commands typed.
$ history ... 2017 man date 2018 date %F 2019 man date 2020 date -u 2021 man date 2022 date +%Y 2023 date +%F 2024 date +%s 2025 cal 2026 cal -3 2027 uname -a 2028 who 2029 w 2030 ping webcode.me 2031 df -h 2032 ping 2033 man ping 2034 ping -c 4 webcode.me 2035 man ping 2036 history ...
We show a partial list of executed commands.
curl command
The curl command can be used to generate HTTP requests.
$ curl webcode.me
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>My html page</title>
</head>
<body>
<p>
Today is a beautiful day. We go swimming and fishing.
</p>
<p>
Hello there. How are you?
</p>
</body>
</html>
We generate a GET request to a web page; we get a HTML document printed to the console.
$ curl -I webcode.me HTTP/1.1 200 OK Server: nginx/1.6.2 Date: Sat, 07 Jan 2023 12:05:49 GMT Content-Type: text/html Content-Length: 394 Last-Modified: Sun, 23 Jan 2022 10:39:25 GMT Connection: keep-alive ETag: "61ed305d-18a" Accept-Ranges: bytes
With the -I option, we generate a HEAD request, which returns the
header of the document containing some metadata.
wget command
The wget is a non-interactive network retriever.
$ wget -q webcode.me/words.txt $ wget -q webcode.me/thermopylae.txt
With the wget command, we dowload two small text files. The
-q (quiet) option supresses the output of the command.
$ ls thermopylae.txt words.txt
ls command
The ls command lists the contents of the current directory; we have
two files.
$ ls -l total 8 -rw-rw-r-- 1 jano jano 226 júl 26 2021 thermopylae.txt -rw-rw-r-- 1 jano jano 140 júl 26 2021 words.txt
With the -l we get a long listing format. We get additional
information including file permissions, ownership, size, and date of last
modification.
wc command
The wc command counts the number of lines, words, and bytes in the
file.
$ wc thermopylae.txt 4 38 226 thermopylae.txt
The thermopylae.txt file has 4 lines, 38 words, and 226 bytes.
$ wc -l thermopylae.txt 4 thermopylae.txt $ wc -w thermopylae.txt 38 thermopylae.txt $ wc -c thermopylae.txt 226 thermopylae.txt
We can get the information separately with the corresponding options.
cat command
The cat command concatenates files and prints them on the console.
The command is often used to display the contents of small files.
$ cat thermopylae.txt The Battle of Thermopylae was fought between an alliance of Greek city-states, led by King Leonidas of Sparta, and the Persian Empire of Xerxes I over the course of three days, during the second Persian invasion of Greece.
We show the contents of the thermopylae.txt file.
cp command
The cp command is used to copy files and directories.
$ cp thermopylae.txt thermopylae2.txt
With the cp command, we create a copy of the thermopylae.txt file.
The new file is called thermopylae2.txt.
$ echo "The battle took place simultaneously with the naval battle at Artemisium." >> thermopylae2.txt
With the echo command and the >> operator, we append a new
line to the thermopylae2.txt file.
$ cat thermopylae2.txt The Battle of Thermopylae was fought between an alliance of Greek city-states, led by King Leonidas of Sparta, and the Persian Empire of Xerxes I over the course of three days, during the second Persian invasion of Greece. The battle took place simultaneously with the naval battle at Artemisium.
We check the contents of the file with cat; it contains the new
line.
diff command
The diff command compares the two text files line by line.
$ diff thermopylae.txt thermopylae2.txt 4a5 > The battle took place simultaneously with the naval battle at Artemisium.
The output tells that the 5th line from the second file must be appended to the 4th line to make the files identical. Lines preceded by a < are lines from the first file. Lines preceded by > are lines from the second file. The special characters are a (add), d (delete), and c (change).
head command
The head command prints the first n lines (defaults to ten) of each
file to standard output.
$ head words.txt sky blue falcon rock wood forest book small tension war
The head command prints the first ten lines of a file.
$ head -n 3 words.txt sky blue falcon
With the -n option, we can specify the number of lines to display.
$ head -n 3 words.txt thermopylae.txt ==> words.txt <== sky blue falcon ==> thermopylae.txt <== The Battle of Thermopylae was fought between an alliance of Greek city-states, led by King Leonidas of Sparta, and the Persian Empire of Xerxes I over the course of three days, during the second Persian invasion of Greece.
We can specify multiple files.
tail command
The tail command prints the last n lines (defaults to ten) of each
file to standard output.
$ tail words.txt pen purple bow rock falcon owl bear wolf fox storm
The tail command prints the last ten lines.
$ head -4 words.txt sky blue falcon rock $ tail -3 words.txt wolf fox storm
We can specify how many first/last lines to output.
mkdir command
The mkdir command creates a new directory.
$ mkdir docs
We create a new directory called docs.
$ ls -F docs/ thermopylae2.txt thermopylae.txt words.txt
The -F option appends indicators to the files; the /
tells that docs is a directory.
mv command
The mv command moves or renames files and directories.
$ mv thermopylae2.txt docs/
The mv command moves the given file to the directory.
tree command explicitly
via the apt command.
$ ls docs/ thermopylae2.txt
We list the contents of the docs directory; it contains one file.
Some commands may not installed on our machine by default. For instance on
Debian Linux, we need to install the tree command explicitly
via the apt command.
apt command
The apt provides a high-level commandline interface for the package
management system.
$ sudo apt install tree
The apt is a Debian-specific package manager. Here we also assume
that the sudo command is installed on the system and the user can
run sudo command.
tree command
The tree command lists the contents of the current directory in
a tree-like format.
$ tree . ├── docs │ └── thermopylae2.txt ├── thermopylae.txt └── words.txt 1 directory, 3 files
We can see the files and directories that we have created so far.
touch command
The touch command updates the access and modification times of each
file to the current time. It the file does not exist, it is created.
$ touch vals.txt $ ls -s vals.txt 0 vals.txt
With touch, we create an empty file called vals.txt. The
ls-s command prints the size of the file. We can see that it is
empty.
$ echo -e "8\n9\n11\n12\n7\n6\n3\n2\n4\n1\n5" >> vals.txt $ cat vals.txt 8 9 11 12 7 6 3 2 4 1 5
We insert 11 numbers into the vals.txt file with echo.
The -e option of echo evaluates backslash escapes.
$ ls -l vals.txt -rw-rw-r-- 1 jano jano 24 jan 7 13:24 vals.txt
Now the file has 24 bytes.
$ cat -E vals.txt 8$ 9$ 11$ 12$ 7$ 6$ 3$ 2$ 4$ 1$ 5$
There are 13 characters in the file and 11 newline characters; 13 and 11 is 24.
The -E option of cat prints the $ at newline
characters.
$ ls -l vals.txt | awk '{print $5}'
24
We can use the awk command to print only the size information; we
output the fifth column of the row.
sort command
The sort command sorts lines of text files.
$ sort words.txt | head bear blue book bow cloud cup falcon falcon forest fox
The sort command sorts the lines of text files. In our example, we sort the words and print the first ten lines.
$ sort -r words.txt | head wood wolf water warm war tension storm snow small sky
With the -r option, we sort in reverse order.
$ sort -n vals.txt 1 2 3 4 5 6 7 8 9 11 12
With the -n option, we sort the values numerically.
$ awk '{ print $0, "has", length($0), "chars"}' words.txt
sky has 3 chars
blue has 4 chars
falcon has 6 chars
rock has 4 chars
wood has 4 chars
forest has 6 chars
book has 4 chars
small has 5 chars
tension has 7 chars
war has 3 chars
water has 5 chars
warm has 4 chars
cup has 3 chars
...
The awk is a very complex command. Here we print the length of each
of the words in the words.txt file. The $0 is the
entire input record, one line from the file. The length function
gives the size of the given record.
$ ls docs thermopylae.txt vals.txt words.txt
At this moment, we have these files.
rm command
The rm command removes files or directories.
$ rm *.txt
We remove all text files with the rm command.
$ rm docs/thermopylae2.txt $ rmdir docs/
We remove a directory with rmdir command. The directory must be
empty before being deleted. We can also use the rm -rf command
to delete a directory in one go. Note that this command is dangerous and should
be used cautiosly.
$ ls
The directory is empty.
In this article we have presented basic Linux shell commands.
