Bash — Essential Commands Cheat Sheet

Navigation & File System#

pwd                      # Current directory
cd /path/to/dir          # Change directory
cd ~                     # Home
cd -                     # Previous directory
ls -la                   # List all with details
ls -lhS                  # Sort by size, human-readable
tree -L 2                # Tree view, 2 levels
du -sh */                # Size of each subdir
df -h                    # Disk usage by filesystem

File Operations#

# Create
touch file.txt           # Create/update timestamp
mkdir -p a/b/c           # Create nested dirs

# Copy / Move
cp -r src/ dest/         # Copy directory
mv old.txt new.txt       # Move / rename
rsync -av src/ dest/     # Sync with progress

# Delete
rm -rf directory/        # Delete recursively (careful!)
find . -name "*.tmp" -delete  # Find and delete

# View
cat file.txt             # Print file
less file.txt            # Page through (q to quit)
head -n 20 file.txt      # First 20 lines
tail -f /var/log/app.log # Follow live log

Pipes & Redirects#

cmd > file.txt           # Stdout → file (overwrite)
cmd >> file.txt          # Stdout → file (append)
cmd 2> err.txt           # Stderr → file
cmd &> all.txt           # Both stdout + stderr
cmd < input.txt          # Stdin from file
cmd1 | cmd2              # Pipe stdout to cmd2
cmd1 | tee file.txt | cmd2  # Pipe and also write file

Finding Files#

find . -name "*.log"             # By name
find . -type f -size +10M        # Files > 10 MB
find . -mtime -7                 # Modified last 7 days
find . -name "*.sh" -exec chmod +x {} \;  # Find & execute
grep -r "pattern" ./src/         # Recursive content search
grep -rn "TODO" . --include="*.py"  # With line numbers, filtered

Text Processing#

# grep
grep -i "error" app.log          # Case-insensitive
grep -v "DEBUG" app.log          # Invert match
grep -E "warn|error" app.log     # Extended regex

# sed
sed 's/old/new/g' file.txt       # Replace all
sed -i 's/localhost/prod.db/g' config.env    # In-place
sed -n '10,20p' file.txt         # Print lines 10-20

# awk
awk '{print $1, $3}' file.txt    # Print fields 1 and 3
awk -F: '{print $1}' /etc/passwd # Custom delimiter
awk 'NR==5' file.txt             # Print line 5
awk '{sum+=$1} END{print sum}'   # Sum a column

# sort / uniq
sort -k2 -n file.txt             # Sort by 2nd column numerically
sort file.txt | uniq -c | sort -rn  # Count + sort by frequency

# cut / wc
cut -d: -f1,3 /etc/passwd        # Cut fields 1 and 3
wc -l file.txt                   # Count lines

Variables & Strings#

NAME="Alice"
echo "Hello $NAME"
echo "${NAME:-default}"          # Use default if empty
echo "${#NAME}"                  # String length
echo "${NAME:0:5}"               # Substring
echo "${NAME,,}"                 # Lowercase
echo "${NAME//old/new}"          # Replace all

# Special vars
$0   # Script name
$1   # First argument
$@   # All arguments
$#   # Argument count
$?   # Last exit code
$$   # Current PID

Conditionals & Loops#

# if / else
if [[ -f file.txt ]]; then echo "exists"; fi
if [[ "$A" -gt 10 ]]; then echo "big"; else echo "small"; fi

# Common tests
[[ -f file ]]    # File exists
[[ -d dir  ]]    # Dir exists
[[ -z "$V" ]]    # Empty string
[[ -n "$V" ]]    # Non-empty string

# for
for i in {1..5}; do echo $i; done
for f in *.txt; do echo "$f"; done

# while
while IFS= read -r line; do echo "$line"; done < file.txt

Functions#

greet() {
  local name="$1"
  echo "Hello, $name!"
}
greet "Alice"   # Hello, Alice!

# Return a value via stdout
add() { echo $(($1 + $2)); }
result=$(add 3 7)   # result=10

Process Management#

command &        # Run in background
jobs             # List background jobs
fg %1            # Bring job 1 to foreground
kill -9 <PID>    # Force kill
nohup cmd &      # Survive terminal close
wait             # Wait for all background jobs

Useful One-Liners#

# Watch command every 2s
watch -n 2 'df -h'

# Check port is open
nc -zv hostname 443

# Disk usage top 20 dirs
du -sh */ | sort -rh | head -20

# Count files by extension
find . -type f | sed 's/.*\.//' | sort | uniq -c | sort -rn

# JSON pretty print
echo '{"a":1}' | jq .
cat file.json | python3 -m json.tool

# Generate random password
openssl rand -base64 16

# Base64 encode/decode
echo "hello" | base64
echo "aGVsbG8K" | base64 -d

# Archive / extract
tar -czf archive.tar.gz dir/      # Create
tar -xzf archive.tar.gz           # Extract

Script Template#

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

log()  { echo "[$(date '+%F %T')] $*"; }
die()  { log "ERROR: $*"; exit 1; }

main() {
  [[ $# -lt 1 ]] && die "Usage: $0 <arg>"
  log "Starting with: $1"
  # your logic
  log "Done"
}

main "$@"