Linux commands

A non-exhaustive list of common linux command you will likely need

File and directory

Command	Description
pwd	Return path to current directory.
ls	List directories and files here.
ls dir	List directories and files in a directory.
ls -d */	List the name of all subdirectory.
ls -a	List all files including hidden files.
ls -lh	List including more data in readable format.
cd dir	Change directory.
cd	Go to home directory.
pushd dir	Save current directory (push onto stack) and go to dir.
popd dir	Return (pop from the stack) to last saved directory.
dirs	List all saved directories (the stack).
touch file	Create an empty file.
mkdir dir	Create an empty directory.
ln -s file	Create a soft link here to file/dir
mv dir1 dir2	Move or renames a file.
cp file1 file2	Copy file1 to file2.
cp -r dir1 dir2	Copy dir1 to dir2 including subdirectories.
rmdir dir	Remove an empty directory.
rm file	Remove a file.
rm -r dir	Remove a directory and its subdirectories and files.
rm -f file	Remove a file, suppress all warning.
find dir -name pattern	Search for file name matching pattern in dir.

Text viewing

Command	Description
less file	View a file.
less -N file	View file with line numbers.
less -S file	View file, wrap long lines.
cat file	Print file to STDOUT.
tac file	Print file to STDOUT in reverse line order.
head file	Print first lines from a file.
head -n 5 file	Print first 5 lines from a file.
tail file	Print last lines from a file.
tail -n 5 file	Print last 5 lines from a file.
grep str file	Display lines containing str in file.
grep -c 'pattern' file	Count lines matching a pattern.
sort file	Sort lines from a file.
sort -u file	Sort and return unique lines.
uniq -c file	Filter adjacent repeated lines.
wc file	Count file for line, word and characters.
wc -l file	Count number of line for file.
diff file1 file2	Show difference between file1 and file2.
cut -f 1,3 file	Retrieve data from 1,3 columns in a tab-delimited file.

Text editing

Command	Description
paste file1 file2	Join file1 and file2 line by line.
truncate -s size file	Remove contents in file.
nano -S file	Nano editor with smooth scrolling.

Compression

Command	Description
tar -cf file.tar dir	Group files.
tar -xf file.tar	Ungroup files.
tar -zcf file.tar.gz dir	Group and compress files.
tar -zxf file.tar.gz	Extract and ungroup files.

Remote Access

Command	Description
wget url	Download url.
ssh user@server	SSH to a server.
scp -r local_dir user@server:remote_dir	Copy file from local to remote computer.
scp -r user@server:remote_dir local_dir	Copy file from remote to local computer.

IO redirection

Command	Description
cmd > file	Write stdout to file.
cmd >> file	Append stdout to file.
cmd	tee file
cmd	tee -a file
cmd 2>&1	Redirect stderr to stdout.
cmd1	cmd2
cmd < file	Read file as stdin.
cmd << eof-str	Use multiline text as stdin, terminated by the specific sequence eof-str.
text
eof-str
cmd <<< str	Use string as stdin.

File attributes

Command	Description
chmod +x file	Set execute permission to file.
chmod -x file	Unset execute permission to file.
chmod IJK file	Set permission denoted by IJK to file. I, J, K = 0 to 7, to calculate, sum all permissions, read=4, write=2, execute=1.
	I is for user, J is for group, K is for everyone.
chmod -R IJK dir	Set permission denoted by IJK to dir and all subdirectories and files.
chown -R user:group dir	Change the ownership of dir and all subdirectories and files.

Misc

Command	Description
echo string	Print the string to STDOUT
printf format-str args	C like printf
date	Display current date time information.
time cmd	Time the execution of cmd
sleep N	Wait for N secs.
watch cmd	Repeatedly execute cmd every 2s and display result.
which cmd	Display the resolved command directory.
seq a b incr	Generate a list of number starting from a to b incremented by incr.
yes	Keep saying yes
yes str	Keep saying str, usually used to say "no".

Useful files

Command	Description
Descriptor 0	STDIN
Descriptor 1	STDOUT
Descriptor 2	STDERR
/dev/null	A file that discard information
/dev/zero	A file that provides 0x00
/dev/urandom	A file that provide random bytes
~	Home directory
~+	Directory pointed by PWD
~-	Directory pointed by OLDPWD
.	Current directory
..	Parent directory
/	Root directory
~/.profile	A shell-independent initialization file, not preferred.
~/.bash_profile	Configure environment and preferences for login shell
~/.bashrc	Configure environment and preferences for interactive shell
~/.bash_login	Bash script to execute on login
~/.bash_logout	Bash script to execute before logout
~/.bash_history	Bash command history

Quotes in bash

Command	Description
'string'	Represents a string exactly as is.
"string"	Represents a string exactly, except substitution and escaping
$var	Replace by value of var
${var}	Sometimes you need this for replacing by value of var
$(expr)	Evaluate expr and substitute the result
expr	Evaluate expr and substitute the result
$[arithmetic-expr]	Evaluate arithmetic-expr and substitute value

Read Manual

For details of every command

Command	Description
help	Display bash help.
help cmd	Show usage of built-in commands.
man cmd	Show usage of most commands.
info cmd	Show more info about command.

Others

These are useful: sed, awk, make, rsync, git, some bash or python scripting