Tips | Cheat sheets | Linux Command Library

LinuxCommandLibrary

Clear and reset the terminal

To clear the terminal, use the command below or press Ctrl+L on your keyboard.

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If you screw up the screen by e.g. accidentally reading a binary file with cat or less you might reinitialize the terminal with the reset command.

$ reset

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List of recent commands

Use the history command to list all recent commands.

$ history

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Search command history for query.

$ history | grep [query]

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Or press Ctrl+R to search and execute commands from the history.

Close a frozen window/application

Execute the command and click on the frozen window.

$ xkill

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Or find the process id of an application and kill it.

$ ps ax | grep firefox

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$ [processID] ?? S 0:00.22 firefox

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$ kill [processID]

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This might save you a lot of time. If you e.g. want to delete a file with a very long name you can type the first few characters of the name and press TAB to auto complete the name. If there is more than one possibility and you press TAB twice, you get a list of all possibilities.

Temporary aliases

Save yourself time and create aliases for your most used commands. Aliases are like custom shortcuts.

$ alias [name]="[command]"

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Example: Find out your external IP.

$ alias publicip="curl ifconfig.me"

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Permanent aliases

Use aliases between sessions or even distros.Find out what shell you have:

$ echo 0ドル

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Bash

$ vim ~/.bashrc

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ZSH

$ vim ~/.zshrc

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Fish

$ vim ~/.config/fish/config.fish

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Find a place in the file, where you want to keep the aliases. Usually you find them at the end of the file.

$ alias h="history"

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Chain commands

Automatically execute several commands in a row. Regardless of whether one of the commands fails:

$ command1 ; command2 ; command3

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Separated by double ampersands, the next command is executed only if the previous one was executed successfully.

$ command1 && command2

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Separated by double pipes, the next command is executed only if the previous one failed.

$ command1 || command2

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Command syntax

To find out the syntax of a command, it is best to check the manual page:

$ man [command]

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If there is no man page on your system, which hardly ever happens, you can check if the command has a help page in the most common way:

$ [command] --help

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A very useful tool that gives you general examples of how to use commands is TLDR.

$ tldr [command]

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Cursor navigation

ctrl + u Clear everything before the cursor

ctrl + a To beginning of line

ctrl + e To end of line

ctrl + f Forward one character

ctrl + b Back one character

ctrl + w Cut last word

ctrl + k Clear everything after cursor

ctrl + _ Undo

meta + f Forward one word

meta + b Back one word

These are for the default emacs mode.There is also a [vim](/man/vim) mode:

$ bindkey -v

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Redirection

You can redirect standard input, output and error by adding these sequences after a command.

> send output to file (overwriting and destroying whatever is in the file already)

$ echo "Write output to file" > example.txt

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>> append output to file

$ echo "Append this to file" >> example.txt

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< take input from file

$ cowsay < example.txt

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2> send error messages to file (overwriting). (This means that errors can be directed separately from normal output.)

$ rm -vf folder1 file1 > out.txt 2> err.txt

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Special characters in commands

Shell special characters are interpreted by the shell as soon as it is given the command. For example, if you type ls *.bak, the shell translates *.bak to the list of all files in the current folder whose names end in .bak. The ls command never sees the asterisk. So if you want to search for files which actually have an asterisk in their names, you have to escape the asterisk to stop the shell from interpreting it.

\\ escapes itself and other specials

\* stands for anything (including nothing)

$ find ex*.txt

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? stands for any single character

$ find ex?mple.txt

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[] encloses patterns for matching a single character

$ find ex[abc]mple.txt

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() runs the contents of the parentheses in a sub-shell

$ pwd && (cd /etc) && pwd

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; terminates a command pipeline - use it to separate commands on a single line

$ echo Hi ; uname

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'' The contents of the single quotes are passed to the command without any interpretation.

$ find '(echo abc)'*

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`` The contents of the backquotes are run as a command and its output is used as part of this command

$ echo \[uname](/man/uname)\``

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"" The contents of the quotes are treated as one argument; any specials inside the quotes, except for $ and \,円 are left uninterpreted.

$ cd "untitled folder"

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| Pipes allow you to send the output of a command to another command.

$ fortune | cowsay

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& Run a command in the background.

$ cowsay &

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&& Only execute the second command if the first one was successful.

$ ping localhost -c 1 && cowsay great

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|| Only execute the second command if the first one was unsuccessful.

$ ping "not.reachable" -c 1 || cowsay sorry

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>> These symbols are used for redirection.

!! Repeat the last command

$ sudo !!

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!* Change the command, keep all arguments

$ tail !*

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^ Quick history substitution, changing one string to another.

^png^xcf^

# Turns the line into a comment; the line is not processed in any way.

# hint text

Don't confuse shell special characters with special characters in regular expressions. Regular expressions must be protected from the shell by enclosing them in single quotes.

View file permissions

$ ls -l [file]

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Position	Meaning
1	File type: '-' for a regular file, 'd' for a directory, 'l' for a symbolic link.
2-4	Owner permissions (rwx)
5-7	Group permissions (rwx)
8-10	Other permissions (rwx)

Example: `-rwxr--r--` means the owner has read, write and execute permissions, but the group and others have only read permissions.

Modify file permissions

$ chmod [modification] [file]

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Example: Give the group read and write access to the test.txt file.

$ chmod g+rw test.txt

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Permission groups:

u Owner

g Group

o Other

Permission types:

r Read

w Write

x Execute

Operators for the modification command are + (plus) and - (minus).

Set file permissions via binary references

Example: Give the owner read and write permission, the group read permission and no permission to other.

$ chmod 640 test.txt

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The first number represents the owner permissions, the second the group permissions, and the last number the permissions for all other users. The numbers are a binary representation of the rwx string.

Permission	Value
r	4
w	2
x	1

Running commands in the background

If a command is taking a long time, you can suspend it with Ctrl+Z and then resume it in the background.

$ bg

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To bring a background job back to the foreground:

$ fg

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To list all background jobs in the current session:

$ jobs

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If you want a command to keep running even after you log out, use nohup.

$ nohup [command] &

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For long-running tasks or managing multiple terminal sessions, use tmux. It lets you detach and reattach sessions, so your work survives disconnects.

$ tmux new -s mysession

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Detach from a session with Ctrl+B then D. Reattach later with:

$ tmux attach -t mysession

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Scheduling tasks with cron

Edit your user's crontab to schedule recurring tasks.

$ crontab -e

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Each line in the crontab follows a five-field format:

Field	Value
Minute	0 - 59
Hour	0 - 23
Day of month	1 - 31
Month	1 - 12
Day of week	0 - 7 (0 and 7 are Sunday)

Example: Run a backup script every day at 2 AM.

$ 0 2 * * * /home/user/backup.sh

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