pwd
Print working directory
/home/user/projects
ls -la
List all files with details
Shows hidden files, permissions, size
ls -lh
List files with human-readable sizes
-rw-r--r-- 1 user group 1.2M file.tar
cd -
Go to previous directory
Toggle between two directories
pushd /path && popd
Push/pop directory stack
pushd /tmp; work; popd
find . -name '*.txt'
Find files by name pattern
find /var/log -name '*.log' -mtime -7
find . -type f -size +100M
Find files larger than 100MB
find / -type f -size +100M 2>/dev/null
tree -L 2
Show directory tree (2 levels)
tree -L 3 --dirsfirst
du -sh *
Disk usage of current directory items
du -sh /var/log/*
df -h
Disk free space (human-readable)
Shows all mounted filesystems
ls -lt | head -10
10 most recently modified files
Sort by modification time, newest first
cp -r src/ dest/
Copy directory recursively
cp -rp /etc/nginx /etc/nginx.bak
mv file1 file2
Move/rename file
mv old_name.txt new_name.txt
rm -rf dir/
Remove directory and all contents
Be careful โ no recycle bin!
mkdir -p a/b/c
Create nested directories
Creates all intermediate dirs
touch file.txt
Create empty file or update timestamp
touch -t 202501010000 file.txt
ln -s /path/to/file link
Create symbolic link
ln -s /usr/local/bin/python3 /usr/bin/python
tar -czf archive.tar.gz dir/
Create gzipped tarball
tar -czf backup-$(date +%Y%m%d).tar.gz /data
tar -xzf archive.tar.gz
Extract gzipped tarball
tar -xzf archive.tar.gz -C /dest/
zip -r archive.zip dir/
Create zip archive
zip -r site.zip public/
rsync -avz src/ user@host:dest/
Sync files to remote host
rsync -avz --delete /local/ remote:/dest/
diff file1 file2
Show differences between files
diff -u file1.txt file2.txt | less
wc -l file.txt
Count lines in file
wc -l *.log | sort -n
cat file.txt
Print file contents
cat -n file.txt (with line numbers)
less file.txt
Page through file contents
Use arrow keys, q to quit, /search
head -n 20 file.txt
Show first 20 lines
head -n 20 /var/log/syslog
tail -f logfile
Follow file as it grows
tail -f /var/log/nginx/access.log
grep -rn 'pattern' dir/
Recursively search for pattern
grep -rn 'TODO' src/ --include='*.ts'
grep -v 'pattern'
Lines NOT matching pattern
grep -v '^#' config.conf (skip comments)
sed 's/old/new/g' file
Replace text (global)
sed -i 's/localhost/production.com/g' config.yml
awk '{print $1,$3}'Print specific columns
awk '{sum+=$2} END{print sum}' data.txtsort -k2 -n file
Sort by column 2 numerically
sort -t',' -k3 -n -r data.csv
sort | uniq -c | sort -rn
Count and rank unique lines
cat access.log | awk '{print $1}' | sort | uniq -c | sort -rn | headcut -d',' -f1,3
Extract comma-separated fields 1,3
cut -d':' -f1 /etc/passwd
tr '[:lower:]' '[:upper:]'
Convert to uppercase
echo 'hello' | tr '[:lower:]' '[:upper:]'
ps aux | grep process
Find process by name
ps aux | grep nginx
kill -9 PID
Force kill process by PID
kill -TERM PID (graceful first)
pkill -f 'pattern'
Kill processes matching pattern
pkill -f 'python my_script.py'
top / htop
Interactive process viewer
htop for a better interface
nohup cmd &
Run command immune to hangups
nohup ./server.sh > server.log 2>&1 &
jobs / fg / bg
Manage background jobs
Ctrl+Z to suspend, bg to resume
time command
Measure command execution time
time npm run build
watch -n 5 'command'
Repeat command every 5 seconds
watch -n 1 'ps aux | grep myapp'
lsof -p PID
List files opened by process
lsof -i :3000 (port 3000)
strace -p PID
Trace system calls of process
strace -e trace=openat ls
curl -I https://example.com
Fetch HTTP headers only
curl -sI https://api.example.com | head -5
curl -X POST -H 'Content-Type: application/json' -d '{...}' urlPOST JSON to endpoint
curl -s -o /dev/null -w '%{http_code}' urlwget -q -O file.tar.gz url
Download file quietly to name
wget -q --show-progress url
ssh user@host -p 2222
SSH with custom port
ssh -i ~/.ssh/key.pem user@host
scp file user@host:/path/
Secure copy to remote
scp -r user@host:/remote/ /local/
netstat -tlnp
Show listening TCP ports + PIDs
ss -tlnp (modern replacement)
ss -s
Socket statistics summary
ss -tlnp | grep :80
ping -c 4 host
Ping host 4 times
ping -i 0.2 -c 100 host
traceroute host
Trace route to host
mtr host (combined ping+traceroute)
nmap -p 80,443 host
Scan specific ports
nmap -sV -p 1-65535 host
chmod 755 file
rwxr-xr-x (owner full, others r+x)
chmod +x script.sh
chmod -R 644 dir/
Set 644 recursively on directory
chmod -R u=rw,go=r dir/
chown user:group file
Change file owner and group
chown -R www-data:www-data /var/www
umask 022
Set default permission mask
umask 027 (group can't write, others nothing)
stat file
Show file metadata and permissions
stat -c '%A %U %G' /etc/passwd
sudo -u user command
Run command as another user
sudo -u postgres psql
visudo
Edit sudoers file safely
Adds user ALL=(ALL) NOPASSWD: ALL
getfacl / setfacl
Get/set POSIX access control lists
setfacl -m u:bob:rw file
VAR="value"
Set local variable (no spaces around =)
NAME="World"; echo "Hello $NAME"
export VAR=value
Export variable to child processes
export NODE_ENV=production
echo ${VAR:-default}Use default if VAR is unset
PORT=${PORT:-3000}readonly VAR=value
Create read-only variable
readonly PI=3.14159
VAR=$(command)
Assign command output to variable
DATE=$(date +%Y-%m-%d)
env
List all environment variables
env | grep PATH
unset VAR
Remove variable
unset MY_SECRET
declare -a arr=(a b c)
Declare array
arr=("one" "two" "three"); echo ${arr[0]}${#VAR}String length
echo ${#HOME}${VAR#prefix}Remove prefix from value
${file%.txt} (remove .txt extension)if [ condition ]; then cmd fi
Basic if statement
if [ -f file.txt ]; then echo "exists"; fi
[[ ... ]]
Extended test โ prefer over [ ]
[[ -n "$VAR" && "$VAR" =~ ^[0-9]+$ ]]
for i in {1..10}; do
cmd
doneLoop over range
for f in *.txt; do echo "$f"; done
while IFS= read -r line; do echo "$line" done < file.txt
Read file line by line
while read line; do ...; done < input.txt
case $VAR in 'a') cmd;; *) default;; esac
Case/switch statement
case "$OS" in linux) apt;; darwin) brew;; esac
cmd1 && cmd2
Run cmd2 only if cmd1 succeeds
make && make install
cmd1 || cmd2
Run cmd2 if cmd1 fails
ping -c1 host || echo 'unreachable'
set -e
Exit script on any error
set -euo pipefail (strict mode)
trap 'cleanup' EXIT
Run cleanup on script exit
trap 'rm -f $TMPFILE' EXIT
function_name() {
local var="value"
echo "$var"
}Define a function with local vars
greet() { local name="$1"; echo "Hello $name"; }$1 $2 $@
Function/script arguments ($1=first...)
$# is number of args, $@ is all args
return 0
Return from function (0=success)
Non-zero return = error
source script.sh (or . script.sh)
Load functions/variables from file
source ~/.bashrc
cmd > file.txt
Redirect stdout to file (overwrite)
ls > files.txt
cmd >> file.txt
Append stdout to file
date >> log.txt
cmd 2> err.txt
Redirect stderr to file
make 2> errors.txt
cmd > out.txt 2>&1
Redirect both stdout and stderr
Capture all output to file
cmd 2>/dev/null
Discard stderr
Suppress error messages
cmd1 | cmd2
Pipe stdout of cmd1 to stdin of cmd2
cat file | sort | uniq -c
tee file.txt
Write to file AND stdout simultaneously
cmd | tee output.txt | grep error
xargs
Build commands from stdin
find . -name '*.log' | xargs rm -f
cmd < file.txt
Redirect file to stdin
mysql -u root < dump.sql
cmd <<EOF text EOF
Here-doc: multi-line stdin
ssh host <<EOF cd /app && git pull EOF
for h in host1 host2; do ssh $h 'uptime'; done
Run command on multiple hosts
Parallel: use & and wait
date +%Y-%m-%dT%H:%M:%S
ISO 8601 timestamp
file_$(date +%Y%m%d_%H%M%S).bak
openssl rand -hex 32
Generate random 32-byte hex string
Good for generating secrets/tokens
python3 -m http.server 8080
Quick HTTP file server
Serve current directory
nc -zv host port
Test TCP connectivity to port
nc -zv db.host 5432
jq '.key' file.json
Parse/query JSON (jq)
curl -s api.url | jq '.data[].name'
!! / !$ / !string
History: last cmd / last arg / last cmd starting with 'string'
sudo !! (re-run with sudo)
CTRL+R
Reverse search command history
Type to filter, Enter to run
column -t -s','
Format CSV as aligned table
cat data.csv | column -t -s','
diff <(cmd1) <(cmd2)
Diff output of two commands
diff <(sort file1) <(sort file2)
#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'
# Script metadata
readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
readonly SCRIPT_NAME="$(basename "${BASH_SOURCE[0]}")"
# Logging helpers
log() { echo "[$(date '+%Y-%m-%d %H:%M:%S')] $*"; }
warn() { log "WARN: $*" >&2; }
err() { log "ERROR: $*" >&2; exit 1; }
# Cleanup on exit
cleanup() {
log "Cleaning up..."
# remove temp files, etc.
}
trap cleanup EXIT
# Validate dependencies
require_cmd() {
command -v "$1" >/dev/null 2>&1 || err "Required command not found: $1"
}
require_cmd curl
require_cmd jq
# Main logic
main() {
local input="${1:-}"
[[ -z "$input" ]] && err "Usage: $SCRIPT_NAME <input>"
log "Processing: $input"
# ... your logic here
}
main "$@"set -euo pipefail is the bash strict mode: -e exits on error, -u treats unset variables as errors, -o pipefail catches errors in pipes.
$0Name of the script$1-$9Positional parameters (arguments)$@All arguments as separate words$*All arguments as a single word$#Number of arguments$?Exit status of last command$$PID of current shell$!PID of last background command$_Last argument of previous command$BASHPIDPID of current bash subshell$LINENOCurrent line number in script$RANDOMRandom integer 0-32767Enter a command or shell concept in the search field and read the matching example before copying it. Start with a small read only operation such as printing the current directory. The example below shows the command itself; its terminal output depends on the directory where you run it. Use the category filter when you need a specific group such as variables, loops, or file operations.
Replace sample paths and variable values before executing a copied command. Quoting matters when a value contains spaces or shell metacharacters, and commands can behave differently across shells. This page is a Bash reference rather than a shell session, so nothing runs when you search or copy. Check the target shell and permissions, especially before using examples that overwrite files, change permissions, or remove directories.
Search: pwd
Copied command: pwd
Purpose: print the current working directory
sh is the POSIX-compliant shell (Bourne shell), available on all Unix systems. Bash (Bourne Again SHell) is a superset of sh with additional features like arrays, extended conditionals, brace expansion, and more. On most Linux systems /bin/sh is bash or dash. Use #!/bin/bash for scripts that need bash-specific features.
Add a shebang line at the top (#!/bin/bash or #!/usr/bin/env bash), then run chmod +x script.sh to make it executable. Run it with ./script.sh or bash script.sh.
2>&1 redirects stderr (file descriptor 2) to the same place as stdout (file descriptor 1). Combined with > you can redirect all output: command > output.txt 2>&1 captures both stdout and stderr to the file.
Single quotes ('') preserve all characters literally โ no variable expansion, no special characters. Double quotes ("") allow variable expansion ($VAR), command substitution ($(cmd)), and escape sequences (\n). Use single quotes when you want literal strings, double quotes when you need variables.