Linux Command Quick Reference

clear

Clear your terminal window. You can also use control + l.

history

Shows all previously entered commands. Use the up arrow and down arrow to navigate command history.

pwd

Prints the full path of the directory you're currently in. Always helpful when you get turned around navigating with cd.

man

Shows the manual page for any command. This is the most important thing you can learn early on — how to find help for things you don't know. Before searching the internet, use man.

man ls       # read all options and examples
man grep

Inside man, press / to search, q to quit. Most commands also accept --help for a quick overview.

Tip: use man to look up every flag listed here. For example, man rm shows the full list of options beyond -r and -f.

ls

Lists the contents of a directory.

ls                # filenames only
ls -l             # details: owner, permissions, size, time
ls -al            # include hidden files (starting with .)
ls -lh            # human-readable file sizes

cd

Changes to a different directory. Directories are case sensitive!

cd ..                    # parent directory
cd /full/path            # absolute path from root
cd mydir                 # relative path (from current directory)
cd ~/mydir               # relative path in your home directory
cd ~                     # home directory

mkdir

Creates a directory.

mkdir -p a/b/c     # create nested directories automatically
mkdir -v mydir     # verbose output
mkdir my\ dir      # directories with spaces: escape the space

touch

Creates a blank file. If the file exists, it updates the timestamp without changing contents.

cp

Copies files or directories.

cp file1.txt file2.txt          # copy a file
cp -r mydir mydir-copy          # copy a directory (recursive)
cp -p file1.txt file2.txt       # preserve permissions/timestamps

rm

Removes files and directories. THIS ACTION CANNOT BE UNDONE!!

rm myfile.txt      # remove a file
rm -rf mydir       # remove directory recursively (force)
rm -v myfile.txt   # verbose output

rmdir

Removes an empty directory only. If there's content inside, use rm -r instead.

mv

Moves or renames files and directories.

mv oldname.txt newname.txt      # rename
mv file.txt /path/to/dest/      # move to directory

cat

Displays the contents of a file on the terminal. Not suitable for large files — use less instead.

cat file.txt

less

Opens a file in scrollable read-only mode. Press j to scroll down, k to scroll up. Press q to exit. Press / to search, n/N for next/previous match.

echo

Prints text to the terminal or writes it into a file using redirection.

echo "content" > file.txt   # overwrite
echo "line" >> file.txt     # append

grep

Searches for text in files.

grep "word" file.txt           # search a file
grep -R "word" /path/to/dir/   # search recursively
grep -i "word" file.txt        # case-insensitive
grep -c "word" file.txt        # count matches
grep -n "word" file.txt        # show line numbers
grep -v "error" logfile.txt    # invert matching

find

Searches for files and directories by name, type, or size.

find . -name "*.txt"           # by name
find . -type d -name "logs"    # by type (directory)
find . -type f -size +100M     # files larger than 100MB

Pipe (|)

The pipe symbol | chains commands together, sending the output of one as input to the next.

ls -t | head -n 5

Shows the 5 most recently modified files. ls -t orders by modification time, and head limits the output.

sort

Sorts lines of input.

sort file.txt
sort -n numbers.txt   # numeric sort
sort -r file.txt      # reverse
sort -u file.txt      # unique only

sed

Finds and replaces text in files.

sed 's/old/new/g' file.txt

The g replaces all occurrences per line. Redirect output to a new file or use -i to edit in-place.

> and >>

ls > filelist.txt           # overwrite
echo "line" >> file.txt     # append
sort < unsorted.txt > sorted.txt   # redirect from file

chmod

Changes file and directory permissions. Four digit notation: 4=read, 2=write, 1=execute.

ls -l                              # see current permissions: drwxr-xr-x

chmod 755 script.sh    # rwxr-xr-x
chmod 644 file.txt     # rw-r--r--
chmod 600 secret.key   # rw-------

chmod u+x script.sh    # add execute for owner
chmod g-w file.txt     # remove write for group

ps

Shows running processes.

ps aux                # all processes
ps aux | grep nginx   # find a specific process

kill

Stops a running process by its process ID (PID).

kill 1234             # polite request (SIGTERM)
kill -9 1234          # force kill (SIGKILL - use as last resort)
pkill nginx           # kill by name

df

Shows available disk space.

df -h                 # human-readable sizes

Check this if you get "No space left on device" errors.

du

Shows disk usage of a file or directory.

du -sh mydir/         # total size in human-readable format

tar

tar -czvf archive.tar.gz mydir/   # create gzipped archive
tar -xzvf archive.tar.gz           # extract
tar -tzvf archive.tar.gz           # list contents

Variables

The shell stores values in named variables, referenced with $.

export MYVAR="hello"
echo $MYVAR

Common built-ins: $? (last exit status), $HOME, $PATH, $USER.

Wildcards

Match multiple files with a single pattern.

rm *.txt              # all .txt files

Aliases

A shortcut for a longer command. Define in ~/.bashrc.

alias ll='ls -la'
alias cls='clear'

List all with alias, remove one with unalias ll.

which

Finds the full path to a command:

which python

Job control

Run commands in the background:

cp largefile.txt /dest/ &
jobs
fg %1

Press Ctrl + Z to pause, then fg %1 or bg %1 to resume.