Bash Cheatsheet

Navigation

Command	Description
pwd	Print current directory
cd <dir>	Change directory
cd ~	Go to home directory
cd -	Go to previous directory
ls	List directory contents
ls -la	List all files including hidden, long format
pushd <dir>	Push directory onto stack and cd to it
popd	Pop directory from stack and return to it

File Operations

Command	Description
cp src dst	Copy file
cp -r src dst	Copy directory recursively
mv src dst	Move or rename file/directory
rm <file>	Delete file
rm -rf <dir>	Delete directory and contents (use with care)
mkdir <dir>	Create directory
mkdir -p a/b/c	Create nested directories
touch <file>	Create empty file or update timestamp
ln -s target link	Create symbolic link
find . -name "*.log"	Find files matching pattern
chmod 755 <file>	Set file permissions
chown user:group <file>	Change file owner and group

Viewing Files

Command	Description
cat <file>	Print file contents
less <file>	Paginated viewer (q to quit, / to search)
head -n 20 <file>	Show first 20 lines
tail -n 20 <file>	Show last 20 lines
tail -f <file>	Follow file as it grows (useful for logs)
grep "pattern" <file>	Search file for pattern
grep -r "pattern" .	Recursive search in current directory
wc -l <file>	Count lines in file
sort <file>	Sort lines alphabetically
uniq	Remove duplicate adjacent lines (use after sort)

Redirection & Pipes

Syntax	Description
cmd > file	Redirect stdout to file (overwrite)
cmd >> file	Redirect stdout to file (append)
cmd < file	Feed file as stdin to cmd
cmd1 | cmd2	Pipe stdout of cmd1 to stdin of cmd2
cmd 2> err.log	Redirect stderr to file
cmd &> file	Redirect both stdout and stderr to file
cmd 2>/dev/null	Suppress stderr
cmd1 && cmd2	Run cmd2 only if cmd1 succeeds
cmd1 || cmd2	Run cmd2 only if cmd1 fails
cmd1 ; cmd2	Run both regardless of exit codes

Variables

Syntax	Description
VAR=value	Assign (no spaces around =)
$VAR or ${VAR}	Expand variable
${VAR:-default}	Use default if VAR is unset or empty
${VAR:?error}	Exit with error if VAR is unset
readonly VAR=value	Make variable read-only
export VAR	Make variable available to child processes
unset VAR	Remove variable
${#VAR}	Length of variable value
$0, $1, $2…	Script name, positional args
$@	All arguments as separate words
$#	Number of arguments
$?	Exit code of last command
$$	PID of current shell

Conditionals

# if / elif / else
if [[ "$VAR" == "hello" ]]; then
  echo "greeting"
elif [[ "$VAR" == "bye" ]]; then
  echo "farewell"
else
  echo "other"
fi

# File tests
if [[ -f "$FILE" ]]; then echo "is a file"; fi
if [[ -d "$DIR" ]]; then echo "is a directory"; fi
if [[ -z "$STR" ]]; then echo "empty string"; fi
if [[ -n "$STR" ]]; then echo "non-empty string"; fi
if [[ -e "$PATH" ]]; then echo "exists"; fi

Test Flag	Meaning
-f	Is a regular file
-d	Is a directory
-e	Exists (file or dir)
-z	String is empty
-n	String is non-empty
-r / -w / -x	File is readable / writable / executable
-eq / -ne / -lt / -gt	Numeric: equal / not equal / less / greater

Loops

# for loop over values
for item in a b c; do
  echo "$item"
done

# for loop over files
for f in *.txt; do
  echo "$f"
done

# C-style for loop
for ((i=0; i<5; i++)); do
  echo "$i"
done

# while loop
while [[ $count -lt 10 ]]; do
  ((count++))
done

# until loop
until [[ $count -ge 10 ]]; do
  ((count++))
done

Functions

# Define
greet() {
  local name="$1"       # local variable
  echo "Hello, $name!"
  return 0              # exit code
}

# Call
greet "World"
result=$(greet "World") # capture output

Keyboard Shortcuts

Shortcut	Action
Ctrl+C	Interrupt (kill) current process
Ctrl+Z	Suspend current process (resume with fg)
Ctrl+D	Send EOF / exit shell
Ctrl+L	Clear screen
Ctrl+R	Search command history (reverse search)
!!	Re-run last command (e.g. sudo !!)
Ctrl+A	Move cursor to start of line
Ctrl+E	Move cursor to end of line
Ctrl+W	Delete word to the left
Tab	Autocomplete command or path

Process Management

Command	Description
ps aux	List all running processes
kill <pid>	Send SIGTERM to process
kill -9 <pid>	Force kill (SIGKILL)
pkill <name>	Kill processes by name
jobs	List background jobs
bg %1	Resume job 1 in background
fg %1	Bring job 1 to foreground
nohup cmd &	Run cmd immune to hangups, in background