Linux Command Line Cheatsheet for Developers

Fluency in the Linux terminal multiplies your productivity as a developer. Whether you're SSH'd into a server, working in CI/CD, or debugging a container, these are the commands you'll use daily.

Navigation and File Operations

# Navigation
pwd                    # print working directory
cd /var/log            # absolute path
cd ../..               # two levels up
cd -                   # go back to previous directory
ls -lah                # list all files with human-readable sizes
tree -L 2              # directory tree, 2 levels deep

# File operations
cp -r src/ dst/        # copy directory recursively
mv old.txt new.txt     # move/rename
rm -rf dist/           # delete directory (careful!)
mkdir -p a/b/c         # create nested directories
touch file.txt         # create empty file or update timestamp

# Links
ln -s /actual/path /symlink  # create symlink
ls -la | grep "^l"           # list symlinks

# Find files
find . -name "*.log" -type f
find . -name "*.ts" -newer package.json
find /var/log -mtime -1       # modified in last 24 hours
find . -size +10M             # larger than 10MB
find . -name "node_modules" -prune -o -name "*.ts" -print  # exclude dir

Text Search and Processing

# grep — search for patterns
grep "error" app.log
grep -r "TODO" src/                   # recursive
grep -rn "deprecated" src/            # with line numbers
grep -v "DEBUG" app.log               # invert — lines NOT matching
grep -E "error|warning" app.log       # extended regex
grep -c "404" access.log              # count matching lines
grep -l "TODO" src/**/*.ts            # only print filenames

# Find process using a port
grep -r "localhost:3000" ./

# awk — field processing
awk '{print $1, $3}' access.log       # print columns 1 and 3
awk -F',' '{print $2}' data.csv       # CSV — use comma delimiter
awk '{sum += $5} END {print sum}' log  # sum column 5
awk 'NR>1 && $3 > 100 {print $0}' f   # filter: skip header, col3 > 100

# sed — stream editor
sed 's/foo/bar/g' file.txt            # replace foo with bar
sed 's/foo/bar/g' file.txt > new.txt  # save to new file
sed -i 's/foo/bar/g' file.txt         # in-place edit
sed -i.bak 's/foo/bar/g' file.txt     # in-place with backup
sed '/^#/d' config.txt                # delete comment lines
sed -n '10,20p' file.txt              # print lines 10-20

File Content and Manipulation

# View files
cat file.txt                # print entire file
less file.txt               # paginated (q to quit, / to search)
head -20 file.txt           # first 20 lines
tail -50 file.txt           # last 50 lines
tail -f app.log             # follow (live updates)
tail -f app.log | grep ERROR # follow + filter

# Count
wc -l file.txt              # count lines
wc -w file.txt              # count words

# Sort and deduplicate
sort file.txt
sort -r file.txt            # reverse
sort -n numbers.txt         # numeric sort
sort file.txt | uniq        # remove duplicate lines
sort file.txt | uniq -c     # count occurrences

# Pipe combinations
cat access.log | grep "404" | awk '{print $7}' | sort | uniq -c | sort -rn | head -20
# → top 20 404 URLs

Permissions

# Permission format: -rwxr-xr-x
# [type][owner][group][others]
# r=4, w=2, x=1

chmod 755 script.sh        # rwxr-xr-x
chmod 644 config.txt       # rw-r--r--
chmod +x script.sh         # add execute for all
chmod -R 755 public/       # recursive

chown user:group file.txt  # change owner and group
chown -R www-data:www-data /var/www/

# Common permissions
# 777 → everyone can do everything (dangerous)
# 755 → owner: all; others: read+execute (directories, scripts)
# 644 → owner: read+write; others: read only (config files)
# 600 → owner only (private keys: ~/.ssh/id_rsa)

# Secure SSH key (required by SSH)
chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_rsa
chmod 644 ~/.ssh/id_rsa.pub

Process Management

# List processes
ps aux                      # all processes
ps aux | grep node          # filter
top                         # interactive process monitor
htop                        # better top (install separately)

# Find and kill
kill 12345                  # SIGTERM (graceful)
kill -9 12345               # SIGKILL (force)
pkill node                  # kill by name
killall node

# Find what's using a port
lsof -i :3000
ss -tulpn | grep :3000
fuser 3000/tcp

# Background jobs
command &                   # run in background
nohup command &             # run after terminal closes
jobs                        # list background jobs
fg %1                       # bring job 1 to foreground
bg %1                       # send to background

# Run command and keep after disconnect
screen -S mysession         # start named session
tmux new -s mysession       # tmux alternative (recommended)

Disk and Memory

# Disk usage
df -h                       # disk space by filesystem
du -sh *                    # size of each item in current dir
du -sh /* 2>/dev/null | sort -rh | head -10  # top 10 largest dirs

# Memory
free -h                     # RAM usage
vmstat 1 5                  # VM stats every 1s, 5 times

Shell Scripting Essentials

#!/bin/bash
set -euo pipefail  # exit on error, undefined var, pipe failure

# Variables
NAME="Alice"
echo "Hello, $NAME"
echo "Files: $(ls | wc -l)"  # command substitution

# Conditionals
if [[ -f "package.json" ]]; then
  echo "Node project"
elif [[ -f "requirements.txt" ]]; then
  echo "Python project"
else
  echo "Unknown"
fi

# Loops
for file in *.log; do
  echo "Processing $file"
  gzip "$file"
done

# Functions
log() {
  echo "[$(date +%H:%M:%S)] $1"
}
log "Starting deployment"

# Read .env file
export $(grep -v '^#' .env | xargs)

Cron Jobs

crontab -e   # edit cron jobs
crontab -l   # list cron jobs

# Format: minute hour day month weekday command
# ┌─ minute (0-59)
# │ ┌─ hour (0-23)
# │ │ ┌─ day of month (1-31)
# │ │ │ ┌─ month (1-12)
# │ │ │ │ ┌─ day of week (0-7, 0=Sun)

0 2 * * *       /usr/bin/backup.sh         # daily at 2 AM
*/15 * * * *    /usr/bin/check_health.sh   # every 15 minutes
0 0 1 * *       /usr/bin/monthly_report.sh # 1st of month at midnight
0 9 * * 1-5     /usr/bin/work_reminder.sh  # weekdays at 9 AM

# Redirect output to log file
0 2 * * * /usr/bin/backup.sh >> /var/log/backup.log 2>&1