Bash / Terminal Commands
Essential commands for navigation, files, search, permissions, processes, network, and archives
Navigation
| Command | Options | Example | Output | Description |
|---|---|---|---|---|
ls
|
-la, -lh, -R |
ls -la /etc |
file list | List directory contents; -l long format, -a hidden files, -h human sizes |
cd
|
-, ~, .. |
cd ~/projects |
changes dir | Change directory; cd - goes back, cd ~ goes home |
pwd
|
|
pwd |
/home/user | Print working directory (full path) |
tree
|
-L n, -a |
tree -L 2 |
tree view | Display directory tree; -L limits depth (may need install) |
find
|
-name -type -mtime |
find . -name '*.log' |
file paths | Search for files/dirs matching criteria |
locate
|
-i |
locate nginx.conf |
file paths | Fast file search using database index; run updatedb first |
File Operations
| Command | Options | Example | Output | Description |
|---|---|---|---|---|
cp
|
-r, -i, -u |
cp -r src/ dst/ |
copies file | Copy files; -r for directories, -i prompt before overwrite |
mv
|
-i, -n |
mv old.txt new.txt |
moves/renames | Move or rename files; -i prompt before overwrite |
rm
|
-r, -f, -i |
rm -rf dist/ |
deleted | Remove files/dirs; -r recursive, -f force — use carefully |
mkdir
|
-p |
mkdir -p a/b/c |
new dir | Create directory; -p creates parent dirs as needed |
touch
|
|
touch index.html |
empty file | Create empty file or update file timestamp |
ln
|
-s |
ln -s /etc/nginx nginx |
symlink | Create hard link; -s for symbolic link |
Viewing Files
| Command | Options | Example | Output | Description |
|---|---|---|---|---|
cat
|
-n, -A |
cat -n file.txt |
file content | Print file; -n adds line numbers, -A shows non-printable chars |
head
|
-n N |
head -n 20 log.txt |
first N lines | Show first lines of file (default 10) |
tail
|
-n N, -f |
tail -f app.log |
last N lines | Show last lines; -f follows new content in real time |
less
|
/search, q |
less large.log |
paged view | Page through file; / to search, q to quit, space to page |
wc
|
-l, -w, -c |
wc -l file.txt |
count | Word count; -l lines, -w words, -c bytes/chars |
Searching & Text Processing
| Command | Options | Example | Output | Description |
|---|---|---|---|---|
grep
|
-r -i -n -v -E |
grep -rn 'error' logs/ |
matched lines | Search text patterns; -r recursive, -i case-insensitive, -n line numbers |
grep -v
|
|
grep -v 'debug' app.log |
non-matching | Invert match — show lines NOT containing pattern |
grep -E
|
|
grep -E 'warn|error' log |
matched lines | Extended regex — use | for OR, + for one-or-more |
awk
|
'{print $N}' |
awk '{print $1}' f |
column value | Pattern-action text processing; $1 first field, $NF last field |
sed
|
-i 's/a/b/g' |
sed -i 's/foo/bar/g' f |
modified text | Stream editor; s/search/replace/g substitutes globally |
sort
|
-n -r -k N |
sort -n numbers.txt |
sorted output | Sort lines; -n numeric, -r reverse, -k sort by column N |
uniq
|
-c, -d |
sort f | uniq -c |
unique lines | Remove duplicate adjacent lines; usually piped after sort |
Permissions
| Command | Options | Example | Output | Description |
|---|---|---|---|---|
chmod
|
755, 644, +x |
chmod +x script.sh |
perms changed | Change file permissions; 755=rwxr-xr-x, 644=rw-r--r-- |
chown
|
-R user:group |
chown -R www-data:www-data /var/www |
owner changed | Change file owner and group; -R recursive |
ls -la
|
|
ls -la /var/www |
perms listing | Show permissions, owner, group, size for all files |
umask
|
022, 027 |
umask 022 |
default perms | Set default permission mask for new files (022 → 644 files) |
sudo
|
-u user |
sudo systemctl restart nginx |
elevated cmd | Run command as superuser; -u to run as different user |
Process Management
| Command | Options | Example | Output | Description |
|---|---|---|---|---|
ps
|
aux, -ef |
ps aux | grep nginx |
process list | List processes; aux=all users, -ef=full format |
top
|
q, k, M |
top |
live view | Interactive process monitor; q quit, k kill, M sort by memory |
htop
|
F3, F9 |
htop |
live view | Enhanced top with colors; F3 search, F9 kill (may need install) |
kill
|
-9, -15 |
kill -9 1234 |
signal sent | Send signal to PID; -15 SIGTERM (graceful), -9 SIGKILL (force) |
killall
|
-9, -u |
killall node |
signal sent | Kill all processes by name |
jobs
|
-l |
jobs -l |
job list | List background/stopped jobs in current shell |
bg / fg
|
%N |
fg %1 |
resumed | bg sends job to background, fg brings to foreground |
Network
| Command | Options | Example | Output | Description |
|---|---|---|---|---|
curl
|
-o -L -X -H -d |
curl -O https://example.com/f |
response | Transfer data via HTTP/FTP; -L follow redirects, -o save to file |
wget
|
-O -r -q |
wget -q https://example.com |
saved file | Download files; -O rename output, -r recursive, -q quiet |
ping
|
-c N |
ping -c 4 google.com |
RTT ms | Test network connectivity; -c limits packet count |
ssh
|
-i -p -L |
ssh user@host -p 2222 |
shell | Secure shell; -i key file, -p port, -L local port forward |
scp
|
-r -P -i |
scp file user@host:~/ |
copied | Secure copy over SSH; -r recursive, -P port (capital) |
netstat
|
-tuln |
netstat -tuln |
port list | Show network connections; -t TCP, -u UDP, -l listening, -n numeric |
ss
|
-tuln |
ss -tuln |
port list | Modern replacement for netstat; faster and more detailed |
Archives & Compression
| Command | Options | Example | Output | Description |
|---|---|---|---|---|
tar -czf
|
-czf out.tar.gz |
tar -czf arc.tar.gz dir/ |
archive | Create gzip compressed tarball; c=create, z=gzip, f=filename |
tar -xzf
|
-xzf file.tar.gz |
tar -xzf arc.tar.gz -C /tmp |
extracted | Extract gzip tarball; x=extract, -C destination directory |
tar -tf
|
|
tar -tf archive.tar.gz |
file list | List contents of tarball without extracting |
zip
|
-r, -9 |
zip -r out.zip dir/ |
zip file | Create zip archive; -r recursive, -9 max compression |
unzip
|
-d, -l |
unzip archive.zip -d out/ |
extracted | Extract zip; -d destination, -l list contents without extracting |
gzip / gunzip
|
-k, -d |
gzip -k file.txt |
compressed | gzip single file; -k keep original, gunzip to decompress |
Environment & Shell
| Command | Options | Example | Output | Description |
|---|---|---|---|---|
env
|
|
env | grep PATH |
var=value | Print all environment variables; pipe with grep to filter |
export
|
|
export NODE_ENV=production |
var set | Set environment variable for current session and child processes |
echo $VAR
|
|
echo $HOME |
value | Print variable value; use ${VAR} for disambiguation in strings |
which
|
|
which node |
path | Show full path of command executable |
alias
|
|
alias ll='ls -la' |
shortcut | Create command shortcut; add to ~/.bashrc for persistence |
source
|
|
source ~/.bashrc |
reloaded | Execute file in current shell context (also: . ~/.bashrc) |
history
|
!N, !! |
history | tail -20 |
cmd list | Show command history; !! repeats last, !N runs Nth command |
Git Quick Reference
| Command | Options | Example | Output | Description |
|---|---|---|---|---|
git init
|
|
git init my-project |
repo created | Initialize new Git repository in directory |
git clone
|
--depth 1 |
git clone url |
repo cloned | Clone remote repository; --depth 1 for shallow clone |
git status
|
-s |
git status -s |
changes | Show working tree status; -s short format |
git add
|
-A, -p |
git add -p |
staged | Stage changes; -A all, -p interactive patch mode |
git commit
|
-m, --amend |
git commit -m 'msg' |
committed | Commit staged changes; --amend modify last commit |
git push
|
-u origin |
git push -u origin main |
pushed | Push to remote; -u sets upstream tracking branch |
git pull
|
--rebase |
git pull --rebase |
synced | Fetch and integrate remote changes; --rebase instead of merge |
git log
|
--oneline --graph |
git log --oneline -10 |
history | Show commit history; --oneline compact, --graph visual branch |
git stash
|
pop, list |
git stash pop |
restored | Temporarily save uncommitted work; pop to restore |
git diff
|
--staged |
git diff --staged |
diff | Show changes; --staged shows staged but uncommitted changes |
Frequently Asked Questions
sh (Bourne Shell) is the original Unix shell, standardized by POSIX. bash (Bourne Again Shell) is its successor and superset, adding arrays, extended test syntax [[]], arithmetic expansion $(( )), history, tab completion, and more. On most Linux systems /bin/sh is a symlink to bash or dash (a POSIX-only lightweight shell). Scripts using #!/bin/sh should stick to POSIX features for portability; scripts using #!/bin/bash can use bash-specific extensions.
Three steps: (1) Add a shebang line as the very first line: #!/bin/bash. (2) Make it executable with chmod +x script.sh. (3) Run it with ./script.sh (the ./ is needed because the current directory is not in $PATH by default). To run it from anywhere, move it to a directory in your PATH: mv script.sh ~/bin/ and ensure ~/bin is in your PATH.
Bash has three standard streams: stdin (0), stdout (1), stderr (2). Redirect stdout to file: command > file.txt (overwrite) or command >> file.txt (append). Redirect stderr: command 2> errors.txt. Redirect both: command > output.txt 2>&1 or command &> output.txt. Discard output: command > /dev/null 2>&1. Pipe stdout to next command: command1 | command2.
sudo (superuser do) runs a command with root (administrator) privileges. Use it only when required — for example installing system packages, editing files in /etc, or managing services. Avoid running development tools, scripts you did not write, or anything that modifies your home directory as root. Never use sudo with npm install -g unless necessary, as it can corrupt package ownership. The principle of least privilege: use the minimum permissions needed.