Introduction to Bash
Bash (Bourne Again SHell) is a Unix shell and command-line interpreter that serves as the default shell on most Linux distributions and macOS. It provides a powerful interface for interacting with the operating system, automating tasks, and managing files and processes.
Key Concepts
- Commands: Programs or built-in functions that perform specific tasks
- Arguments: Inputs passed to commands to modify their behavior
- Options: Flags that change how commands work (usually start with
-or--) - Pipes: Connect commands together using
| - Redirection: Control input/output streams using
>,>>,< - Variables: Store data for later use
- Scripts: Files containing sequences of commands
1. Basic Command Structure
# Basic syntax: command [options] [arguments] ls -la /home/user # Command with long options ls --all --long /home/user # Multiple commands on one line (separated by ;) cd /tmp; ls -la; pwd # Conditional execution mkdir newdir && cd newdir # Only cd if mkdir succeeds rm file || echo "Failed" # Echo only if rm fails # Command substitution current_date=$(date) echo "Today is $current_date" # Process substitution diff <(ls dir1) <(ls dir2)
2. File System Navigation
Directory Navigation Commands
# pwd - Print Working Directory pwd # Output: /home/username # ls - List Directory Contents ls # List current directory ls -l # Long format with details ls -a # Show all files (including hidden) ls -la # Long format with all files ls -lh # Human-readable sizes ls -lt # Sort by modification time ls -ltr # Reverse time sort ls -R # Recursive listing ls *.txt # List only .txt files # cd - Change Directory cd # Go to home directory cd /var/log # Go to absolute path cd .. # Go up one level cd ../.. # Go up two levels cd - # Go to previous directory cd ~ # Go to home directory cd ~/Documents # Go to Documents in home # tree - Display directory tree (may need installation) tree # Show directory tree tree -L 2 # Limit to 2 levels deep tree -d # Show only directories # pushd/popd - Directory stack pushd /tmp # Save current dir and go to /tmp pushd /var/log # Save and go to /var/log dirs # Show directory stack popd # Return to previous directory popd # Return to original directory
Path Navigation Shortcuts
# Special path characters
. # Current directory
.. # Parent directory
~ # Home directory
- # Previous directory
# Path completion examples
cd /u/lo/b<TAB> # Tab completion expands to /usr/local/bin
# Using wildcards
ls *.txt # All .txt files
ls file?.txt # file1.txt, file2.txt, etc.
ls file[0-9].txt # file0.txt through file9.txt
ls file[a-z].txt # filea.txt through filez.txt
ls {file1,file2}.txt # file1.txt and file2.txt
ls *.{txt,pdf} # All .txt and .pdf files
3. File Operations
Creating and Deleting Files
# touch - Create empty file or update timestamp
touch file.txt # Create empty file
touch -t 202403101200 file # Set specific timestamp
# mkdir - Create directories
mkdir newdir # Create single directory
mkdir -p path/to/nested/dir # Create parent directories as needed
mkdir -m 755 newdir # Create with specific permissions
mkdir dir{1..5} # Create dir1, dir2, dir3, dir4, dir5
# rm - Remove files/directories
rm file.txt # Remove file
rm -i file.txt # Interactive (ask before remove)
rm -f file.txt # Force remove (no prompt)
rm -r directory # Remove directory recursively
rm -rf directory # Force remove directory recursively (careful!)
rm *.tmp # Remove all .tmp files
# rmdir - Remove empty directories
rmdir emptydir # Remove empty directory
rmdir -p path/to/emptydir # Remove nested empty directories
# ln - Create links
ln -s target linkname # Create symbolic link
ln target linkname # Create hard link
Copying and Moving Files
# cp - Copy files/directories cp file.txt copy.txt # Copy file cp -i file.txt copy.txt # Interactive (prompt before overwrite) cp -v file.txt copy.txt # Verbose output cp -r sourcedir destdir # Copy directory recursively cp -a sourcedir destdir # Archive mode (preserve attributes) cp file1.txt file2.txt dir/ # Copy multiple files to directory cp -u source dest # Update (copy only when source is newer) # mv - Move/rename files mv oldname.txt newname.txt # Rename file mv file.txt dir/ # Move file to directory mv -i file.txt dir/ # Interactive move mv -v *.txt backup/ # Move multiple files mv sourcedir/* destdir/ # Move contents of directory mv dir1 dir2 # Rename directory # install - Copy and set attributes install -m 755 script.sh /usr/local/bin/ # Copy with permissions install -d /path/to/new/dir # Create directory
Viewing File Contents
# cat - Concatenate and display files cat file.txt # Display file contents cat file1.txt file2.txt # Display multiple files cat -n file.txt # Show line numbers cat > file.txt # Create file from keyboard input (Ctrl+D to end) # less/more - Page through files less largefile.txt # View file page by page more largefile.txt # Simpler pager # In less: /search, n/N next/prev match, q quit, g/G top/bottom # head - Display first lines head file.txt # First 10 lines head -n 20 file.txt # First 20 lines head -c 100 file.txt # First 100 bytes # tail - Display last lines tail file.txt # Last 10 lines tail -n 20 file.txt # Last 20 lines tail -f logfile.txt # Follow file as it grows tail -f -n 50 logfile.txt # Last 50 lines and follow # nl - Number lines nl file.txt # Display with line numbers nl -b a file.txt # Number all lines nl -w 4 file.txt # Set width of line numbers # od - Octal dump (view binary files) od -x file.bin # Hexadecimal dump od -c file.bin # Character dump # xxd - Hex dump xxd file.bin # Hexadecimal view xxd -r hex.txt > binary.bin # Convert hex back to binary
4. Text Processing
Searching Text
# grep - Search text patterns grep "pattern" file.txt # Search for pattern grep -i "pattern" file.txt # Case-insensitive grep -r "pattern" ./ # Recursive search grep -l "pattern" *.txt # List files with match grep -c "pattern" file.txt # Count matches grep -v "pattern" file.txt # Invert match (lines without pattern) grep -w "word" file.txt # Match whole word only grep -n "pattern" file.txt # Show line numbers grep -A 2 "pattern" file.txt # Show 2 lines after match grep -B 2 "pattern" file.txt # Show 2 lines before match grep -C 2 "pattern" file.txt # Show 2 lines before and after grep -E "pattern1|pattern2" file.txt # Extended regex (OR) grep -e "pattern1" -e "pattern2" file.txt # Multiple patterns # egrep/fgrep - Variants (egrep = grep -E, fgrep = grep -F) egrep "pattern1|pattern2" file.txt # Extended regex fgrep "literal*string" file.txt # Fixed strings (no regex) # ag/silver searcher - Faster alternative ag "pattern" ./ # Fast recursive search
Cutting and Sorting
# cut - Remove sections from lines cut -d':' -f1 /etc/passwd # First field, delimited by : cut -c1-10 file.txt # First 10 characters of each line cut -f1,3 -d',' data.csv # Fields 1 and 3 from CSV # sort - Sort lines sort file.txt # Sort alphabetically sort -n file.txt # Sort numerically sort -r file.txt # Reverse sort sort -u file.txt # Unique sort (remove duplicates) sort -k2 -t',' data.csv # Sort by second field sort -h file.txt # Human-numeric sort (2K, 1G) sort -M file.txt # Sort by month name # uniq - Report or omit repeated lines uniq file.txt # Remove consecutive duplicates uniq -c file.txt # Count occurrences uniq -d file.txt # Only show duplicates uniq -u file.txt # Only show unique lines sort file.txt | uniq # Remove all duplicates # wc - Word count wc file.txt # Lines, words, characters wc -l file.txt # Lines only wc -w file.txt # Words only wc -c file.txt # Bytes only wc -m file.txt # Characters only
Text Transformation
# tr - Translate characters
tr 'a-z' 'A-Z' < file.txt # Convert to uppercase
tr -d ' ' < file.txt # Delete spaces
tr -s ' ' < file.txt # Squeeze repeated spaces
tr '\n' ' ' < file.txt # Replace newlines with spaces
tr -cd 'a-zA-Z0-9' < file.txt # Keep only alphanumeric
# sed - Stream editor
sed 's/old/new/' file.txt # Replace first occurrence per line
sed 's/old/new/g' file.txt # Replace all occurrences
sed -i 's/old/new/g' file.txt # Edit file in-place
sed '/pattern/d' file.txt # Delete lines matching pattern
sed '1,10d' file.txt # Delete lines 1-10
sed -n '5,10p' file.txt # Print lines 5-10
sed 's/^/ /' file.txt # Indent each line
sed 's/$/;/' file.txt # Add semicolon at end of lines
sed 's/ */ /g' file.txt # Replace multiple spaces with one
# awk - Pattern scanning and processing
awk '{print $1}' file.txt # Print first field
awk '/pattern/' file.txt # Print lines matching pattern
awk -F':' '{print $1}' /etc/passwd # Use custom delimiter
awk '{sum+=$1} END {print sum}' file.txt # Sum first column
awk 'NR>1 && NR<10' file.txt # Print lines 2-9
awk '{printf "%s\t%s\n", $1, $2}' file.txt # Formatted output
# paste - Merge lines of files
paste file1.txt file2.txt # Merge side by side
paste -d',' file1.txt file2.txt # Use comma delimiter
paste -s file.txt # Merge all lines into one
# join - Join lines of two files on common field
join -t',' -1 1 -2 1 file1.csv file2.csv # Join on first field
Comparing Files
# diff - Compare files line by line diff file1.txt file2.txt # Show differences diff -u file1.txt file2.txt # Unified format diff -c file1.txt file2.txt # Context format diff -r dir1 dir2 # Compare directories recursively diff -q file1.txt file2.txt # Only indicate if different diff -y file1.txt file2.txt # Side-by-side comparison # cmp - Compare byte by byte cmp file1.bin file2.bin # First difference cmp -l file1.bin file2.bin # All differences with byte numbers # comm - Compare sorted files line by line comm file1.txt file2.txt # 3-column output (file1 only, file2 only, common) comm -12 file1.txt file2.txt # Show only common lines # patch - Apply diff to file patch file.txt < changes.patch # Apply patch patch -R file.txt < changes.patch # Reverse patch
5. File Permissions and Ownership
Permission Commands
# chmod - Change file mode (permissions) chmod 755 script.sh # rwxr-xr-x chmod u+x script.sh # Add execute for user chmod g-w file.txt # Remove write for group chmod o+r file.txt # Add read for others chmod a+x script.sh # Add execute for all chmod -R 755 directory/ # Recursive change # chown - Change file owner chown user file.txt # Change owner chown user:group file.txt # Change owner and group chown :group file.txt # Change group only chown -R user:group directory/ # Recursive change # chgrp - Change group ownership chgrp group file.txt # Change group chgrp -R group directory/ # Recursive change # umask - Set default permissions umask # Show current mask umask 022 # Set mask (files: 644, dirs: 755) umask 077 # Set mask (files: 600, dirs: 700) # ls with permissions ls -l file.txt # Show permissions ls -ld directory/ # Show directory permissions getfacl file.txt # Get ACL (Access Control List) setfacl -m u:user:rw file.txt # Set ACL
Understanding Permission Notation
# Permission types r (4) - Read w (2) - Write x (1) - Execute - (0) - No permission # Permission groups u - User (owner) g - Group o - Others a - All # Examples -rwxr-xr-x 1 user group 1024 Mar 10 10:00 script.sh # -: regular file # rwx: user can read, write, execute # r-x: group can read, execute # r-x: others can read, execute # Numeric notation chmod 644 file.txt # rw-r--r-- (6=4+2 for user, 4 for group, 4 for others) chmod 755 file.txt # rwxr-xr-x (7=4+2+1 for user, 5=4+1 for group/others) chmod 700 file.txt # rwx------ (7 for user, 0 for group, 0 for others)
6. Process Management
Viewing Processes
# ps - Process status ps # Current shell processes ps aux # All processes with details ps -ef # Full format listing ps -u username # Processes for user ps -C command # Processes by command name ps -p PID # Process by PID ps -eo pid,user,command --sort=-pcpu # Custom format sorted by CPU # top - Dynamic process viewer top # Interactive process viewer htop # Enhanced top (may need install) # In top: P (CPU sort), M (memory sort), k (kill), q (quit) # pgrep - Find processes by name pgrep bash # Find bash process IDs pgrep -u user bash # Find user's bash processes pgrep -l bash # Show PID and name # pstree - Show process tree pstree # Tree view of processes pstree -p # Show PIDs pstree username # Processes for user
Managing Processes
# kill - Terminate processes kill PID # Terminate process kill -9 PID # Force kill (SIGKILL) kill -15 PID # Graceful termination (SIGTERM) kill -l # List all signals killall process_name # Kill all processes by name pkill process_name # Kill processes by pattern # bg/fg/jobs - Job control command & # Run in background Ctrl+Z # Suspend foreground job jobs # List jobs bg %1 # Resume job 1 in background fg %1 # Bring job 1 to foreground disown %1 # Remove job from shell control # nice/renice - Process priority nice -n 10 command # Run with lower priority renice -n 5 -p PID # Change priority of running process
System Monitoring
# uptime - System load uptime # How long system has been running # w - Who's logged in w # Show logged-in users # who - Show who is logged in who # List logged-in users who -b # Last boot time who -r # Current runlevel # free - Memory usage free -h # Human-readable memory info free -m # Memory in MB free -s 5 # Update every 5 seconds # vmstat - Virtual memory statistics vmstat 2 10 # Stats every 2 seconds, 10 times # iostat - I/O statistics iostat # CPU and I/O stats iostat -x 2 # Extended stats every 2 seconds # netstat - Network statistics netstat -tulpn # Listening ports netstat -an # All connections ss -tulpn # Modern alternative to netstat # lsof - List open files lsof # All open files lsof -u username # Files opened by user lsof -i :8080 # Processes using port 8080 lsof -p PID # Files opened by process
7. Input/Output Redirection
Basic Redirection
# Standard streams 0 - stdin (standard input) 1 - stdout (standard output) 2 - stderr (standard error) # Output redirection command > file.txt # Redirect stdout to file (overwrite) command >> file.txt # Redirect stdout to file (append) command 2> error.txt # Redirect stderr to file command 2>> error.txt # Append stderr to file command > file.txt 2>&1 # Redirect both stdout and stderr command &> file.txt # Same as above (bash) command > file.txt 2> /dev/null # Stdout to file, stderr to null # Input redirection command < input.txt # Read stdin from file command << EOF # Here document > line1 > line2 > EOF # Here string command <<< "string" # Pass string as stdin
Pipes and Process Substitution
# Pipes - Connect commands command1 | command2 # Pass output of command1 to command2 command1 | command2 | command3 # Chain multiple commands # Common pipe examples ls -la | grep "^d" # List only directories ps aux | grep firefox # Find firefox processes cat file.txt | sort | uniq # Sort and remove duplicates tail -f log.txt | grep error # Monitor log for errors # Named pipes (FIFO) mkfifo mypipe # Create named pipe command1 > mypipe & # Write to pipe in background command2 < mypipe # Read from pipe # Process substitution diff <(ls dir1) <(ls dir2) # Compare directory listings while read line; do echo $line; done < <(command)
Advanced Redirection
# Redirect to multiple files command | tee file.txt # Output to file and stdout command | tee -a file.txt # Append to file command | tee file1.txt file2.txt # Write to multiple files command 2>&1 | tee file.txt # Capture stdout and stderr # Redirect to both stdout and stderr command | tee /dev/stderr # Output to stderr as well # Using /dev/null command > /dev/null # Discard stdout command 2> /dev/null # Discard stderr command &> /dev/null # Discard all output # File descriptors exec 3> file.txt # Open file descriptor 3 for writing echo "Hello" >&3 # Write to fd 3 exec 3>&- # Close fd 3 exec 4< file.txt # Open file descriptor 4 for reading cat <&4 # Read from fd 4 exec 4<&- # Close fd 4
8. Variables and Environment
Shell Variables
# Variable assignment
name="John" # No spaces around =
age=30
echo $name # Reference variable
echo ${name} # Same, but allows concatenation
# Variable types
readonly var="constant" # Read-only variable
declare -i number=42 # Integer variable
declare -r constant="fixed" # Read-only (same as readonly)
declare -l lowercase="HELLO" # Auto-lowercase
declare -u uppercase="hello" # Auto-uppercase
# Array variables
array=(one two three) # Indexed array
echo ${array[0]} # First element
echo ${array[@]} # All elements
echo ${#array[@]} # Array length
array+=(four) # Append element
# Associative arrays (declare -A)
declare -A user
user[name]="John"
user[age]=30
echo ${user[name]}
# Special variables
$0 - Script name
$1, $2, ... - Positional parameters
$# - Number of arguments
$@ - All arguments as separate words
$* - All arguments as single word
$? - Exit status of last command
$$ - Current shell PID
$! - PID of last background command
$- - Current shell options
$_ - Last argument of previous command
Environment Variables
# Environment variables export PATH=$PATH:/usr/local/bin # Add to PATH export EDITOR=vim # Set default editor export LANG=en_US.UTF-8 # Set locale # Common environment variables HOME - User home directory USER - Current username SHELL - Current shell PWD - Current working directory OLDPWD - Previous working directory PATH - Command search path TERM - Terminal type LANG - Language/locale # View environment env # Show all environment variables printenv # Same as env printenv PATH # Show specific variable set # Show all variables and functions # Set for a single command LANG=C command # Run command with specific locale PATH=/custom/path command # Run with custom PATH # Remove variable unset VAR # Remove variable
9. Shell Scripting Basics
Script Structure
#!/bin/bash
# Shebang line - tells system which interpreter to use
# Comments start with #
# Good practice to include description
# Script: example.sh
# Purpose: Demonstrate bash scripting
# Author: User
# Date: 2024-03-10
# Exit on error
set -e # Exit on any error
set -u # Exit on undefined variable
set -o pipefail # Pipe failures cause exit
# Debugging
set -x # Print commands as they execute
set -v # Print input lines as read
# Functions
greet() {
local name=$1 # Local variable
echo "Hello, $name!"
}
# Main script
main() {
greet "World"
}
# Call main if script is executed directly
if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
main "$@"
fi
Conditional Statements
# if-then-else if [ condition ]; then # commands elif [ another condition ]; then # commands else # commands fi # Test conditions [ -f file ] # True if file exists and is regular file [ -d dir ] # True if directory exists [ -e file ] # True if file exists [ -r file ] # True if file is readable [ -w file ] # True if file is writable [ -x file ] # True if file is executable [ -s file ] # True if file size > 0 [ -L file ] # True if file is symbolic link [ -z string ] # True if string is empty [ -n string ] # True if string is not empty [ string1 = string2 ] # String equality [ string1 != string2 ] # String inequality [ num1 -eq num2 ] # Numeric equality [ num1 -ne num2 ] # Numeric not equal [ num1 -gt num2 ] # Numeric greater than [ num1 -ge num2 ] # Numeric greater than or equal [ num1 -lt num2 ] # Numeric less than [ num1 -le num2 ] # Numeric less than or equal # Combining conditions [ condition1 -a condition2 ] # AND [ condition1 -o condition2 ] # OR [ ! condition ] # NOT # Double brackets (bash-specific, more features) [[ -f file && -r file ]] # AND [[ -f file || -d file ]] # OR [[ string == pattern ]] # Pattern matching [[ string =~ regex ]] # Regex matching
Loops
# for loop
for i in 1 2 3 4 5; do
echo "Number: $i"
done
# for loop with range
for i in {1..5}; do
echo "Number: $i"
done
# for loop with step
for i in {1..10..2}; do
echo "Odd: $i"
done
# C-style for loop
for ((i=0; i<5; i++)); do
echo "i = $i"
done
# for loop with files
for file in *.txt; do
echo "Processing: $file"
done
# while loop
count=1
while [ $count -le 5 ]; do
echo "Count: $count"
((count++))
done
# until loop
count=1
until [ $count -gt 5 ]; do
echo "Count: $count"
((count++))
done
# Reading file line by line
while IFS= read -r line; do
echo "Line: $line"
done < file.txt
# Loop control
break # Exit loop
continue # Skip to next iteration
Functions
# Function definition
function myfunc {
echo "Function called"
}
# Alternative syntax
myfunc() {
echo "Function called"
}
# Function with parameters
greet() {
local name=$1
local greeting=${2:-Hello} # Default value
echo "$greeting, $name!"
}
# Function returning value (via echo)
get_name() {
echo "John"
}
name=$(get_name) # Capture output
# Function returning exit status
check_file() {
if [ -f "$1" ]; then
return 0 # Success
else
return 1 # Failure
fi
}
if check_file "test.txt"; then
echo "File exists"
fi
# Variable scope
var="global"
test_scope() {
local var="local" # Local variable
echo "Inside: $var"
}
test_scope
echo "Outside: $var" # Still "global"
10. Advanced Commands
Text Processing Tools
# find - Search for files
find . -name "*.txt" # Find by name
find . -type f -size +1M # Files > 1MB
find . -mtime -7 # Modified in last 7 days
find . -user username # Owned by user
find . -perm 755 # With specific permissions
find . -exec rm {} \; # Execute command on each
find . -print0 | xargs -0 command # Handle spaces in filenames
# xargs - Build and execute command lines
find . -name "*.txt" | xargs rm # Remove all .txt files
find . -name "*.log" | xargs grep "error" # Search in log files
cat files.txt | xargs -n 1 echo # One argument per line
seq 1 10 | xargs -P 4 -I {} ./script {} # Parallel execution
# locate - Fast file search (requires updatedb)
locate file.txt # Find file by name
locate -i "*.pdf" # Case-insensitive pattern
# which - Locate a command
which bash # Show path to bash
which -a ls # Show all matches
# type - Show command type
type ls # ls is aliased to 'ls --color=auto'
type -a echo # All locations of echo
Archive and Compression
# tar - Tape archive tar -cf archive.tar file1 file2 # Create archive tar -xf archive.tar # Extract archive tar -czf archive.tar.gz directory/ # Create gzipped archive tar -xzf archive.tar.gz # Extract gzipped archive tar -cjf archive.tar.bz2 directory/ # Create bzipped archive tar -tvf archive.tar # List contents tar -uf archive.tar newfile # Update archive # gzip/gunzip gzip file.txt # Compress file gunzip file.txt.gz # Decompress gzip -l file.txt.gz # List compression info zcat file.txt.gz # View compressed file # bzip2/bunzip2 bzip2 file.txt # Better compression bunzip2 file.txt.bz2 # Decompress bzcat file.txt.bz2 # View compressed # zip/unzip zip archive.zip file1 file2 # Create zip unzip archive.zip # Extract zip unzip -l archive.zip # List contents zip -r archive.zip directory/ # Zip directory # 7z (p7zip) 7z a archive.7z file.txt # Add to 7z archive 7z x archive.7z # Extract 7z
Networking Commands
# ping - Test network connectivity ping google.com # Ping host continuously ping -c 4 google.com # Ping 4 times ping -i 2 google.com # 2 second interval # curl - Transfer data curl http://example.com # Get webpage curl -o file.html http://example.com # Save to file curl -I http://example.com # Get headers only curl -X POST -d "data" http://example.com # POST request curl -H "Header: value" http://example.com # Custom headers curl -u user:pass http://example.com # Basic auth # wget - Download files wget http://example.com/file.zip # Download file wget -c http://example.com/file.zip # Continue partial download wget -r http://example.com/ # Recursive download wget -O output.html http://example.com # Specify output name wget --limit-rate=200k http://example.com # Limit download speed # ssh - Secure Shell ssh user@host # Connect to host ssh -p 2222 user@host # Custom port ssh -i key.pem user@host # Use identity file ssh -L 8080:localhost:80 user@host # Port forwarding ssh -D 1080 user@host # SOCKS proxy # scp - Secure copy scp file.txt user@host:/path/ # Copy file to remote scp user@host:/path/file.txt . # Copy from remote scp -r directory/ user@host:/path/ # Copy directory # rsync - Remote sync rsync -av source/ user@host:/dest/ # Sync to remote rsync -avz source/ user@host:/dest/ # With compression rsync -av --delete source/ dest/ # Mirror (delete extra files) rsync -av --progress source/ dest/ # Show progress # wget - Download files wget http://example.com/file.zip # Download file wget -c http://example.com/file.zip # Continue partial download wget -r http://example.com/ # Recursive download wget -O output.html http://example.com # Specify output name wget --limit-rate=200k http://example.com # Limit download speed # ssh - Secure Shell ssh user@host # Connect to host ssh -p 2222 user@host # Custom port ssh -i key.pem user@host # Use identity file ssh -L 8080:localhost:80 user@host # Port forwarding ssh -D 1080 user@host # SOCKS proxy # scp - Secure copy scp file.txt user@host:/path/ # Copy file to remote scp user@host:/path/file.txt . # Copy from remote scp -r directory/ user@host:/path/ # Copy directory # rsync - Remote sync rsync -av source/ user@host:/dest/ # Sync to remote rsync -avz source/ user@host:/dest/ # With compression rsync -av --delete source/ dest/ # Mirror (delete extra files) rsync -av --progress source/ dest/ # Show progress
System Information
# uname - System information uname -a # All system info uname -s # Kernel name uname -r # Kernel release uname -m # Machine hardware # lsb_release - Distribution info (Linux) lsb_release -a # All distribution info lsb_release -d # Description lsb_release -c # Codename # hostname hostname # Show hostname hostname newname # Set hostname (as root) # date date # Current date/time date +"%Y-%m-%d %H:%M:%S" # Custom format date -d "yesterday" # Yesterday's date date -s "2024-03-10 12:00:00" # Set date/time (as root) # cal - Calendar cal # Current month cal 2024 # Year calendar cal 12 2024 # December 2024 # bc - Calculator echo "5+3" | bc # Basic calculation echo "scale=2; 10/3" | bc # With decimal places bc -l # Start interactive calculator
User Management
# whoami - Current username whoami # Show current user # id - User identity id # Show user and group IDs id -u # Show UID only id -g # Show GID only id username # Info for specific user # users/who - Who's logged in users # List logged-in users who # Detailed user info who -b # Last boot time # last - Login history last # Show login history last -n 10 # Last 10 logins last username # Logins for specific user # passwd - Change password passwd # Change own password passwd username # Change user's password (as root) # useradd/usermod/userdel - User management (as root) useradd newuser # Add user useradd -m -s /bin/bash newuser # Add with home and shell usermod -aG sudo username # Add user to group userdel username # Delete user userdel -r username # Delete user and home directory # groupadd/groupdel - Group management (as root) groupadd newgroup # Add group groupdel newgroup # Delete group
11. Job Control and Scheduling
Job Control
# Background and foreground command & # Run in background Ctrl+Z # Suspend foreground job jobs # List jobs bg %1 # Resume job in background fg %1 # Bring job to foreground disown %1 # Remove job from job table nohup command & # Run immune to hangups # Process priorities nice -n 10 command # Run with lower priority renice +5 -p PID # Increase niceness renice -5 -p PID # Decrease niceness (higher priority) # Screen/Tmux - Terminal multiplexers screen # Start screen session screen -S sessionname # Named session Ctrl+A d # Detach from screen screen -r # Reattach screen -ls # List sessions tmux # Start tmux session tmux new -s sessionname # New named session Ctrl+B d # Detach tmux attach -t sessionname # Attach tmux ls # List sessions
Task Scheduling
# at - One-time tasks at 14:30 # Schedule command at 14:30 > echo "Task executed" > ~/log.txt > Ctrl+D # End input atq # List pending jobs atrm job_id # Remove job # batch - Run when load is low batch # Schedule when system idle > long_running_command > Ctrl+D # cron - Recurring tasks crontab -l # List cron jobs crontab -e # Edit cron jobs crontab -r # Remove all cron jobs # Crontab format # * * * * * command # │ │ │ │ │ # │ │ │ │ └── Day of week (0-7, 0/7 = Sunday) # │ │ │ └──── Month (1-12) # │ │ └────── Day of month (1-31) # │ └──────── Hour (0-23) # └────────── Minute (0-59) # Examples 0 2 * * * /backup/script.sh # Daily at 2 AM */15 * * * * /monitor/check.sh # Every 15 minutes 0 9-17 * * 1-5 /work/script.sh # Weekdays 9 AM-5 PM hourly # systemd timers (modern alternative) systemctl list-timers # List timers systemctl enable --now timer-name # Enable timer
12. Bash Shortcuts and Productivity
Keyboard Shortcuts
# Navigation Ctrl+A # Go to beginning of line Ctrl+E # Go to end of line Alt+B # Move back one word Alt+F # Move forward one word Ctrl+XX # Toggle between current and previous position # Editing Ctrl+U # Cut from cursor to beginning Ctrl+K # Cut from cursor to end Ctrl+W # Cut word before cursor Alt+D # Cut word after cursor Ctrl+Y # Paste last cut text Ctrl+T # Swap last two characters Alt+T # Swap last two words Ctrl+_ # Undo # History Ctrl+R # Reverse search history Ctrl+G # Exit search mode Ctrl+P # Previous command Ctrl+N # Next command Alt+< # First command in history Alt+> # Last command in history !! # Repeat last command !$ # Last argument of previous command !^ # First argument of previous command !* # All arguments of previous command !string # Repeat last command starting with "string" !?string # Repeat last command containing "string" # Process control Ctrl+C # Terminate foreground process Ctrl+Z # Suspend foreground process Ctrl+D # Exit shell (EOF) Ctrl+L # Clear screen
Aliases and Functions
# Creating aliases
alias ll='ls -la' # List with details
alias ..='cd ..' # Go up one level
alias gs='git status' # Git shortcuts
alias rm='rm -i' # Interactive remove
# Permanent aliases (in ~/.bashrc)
echo "alias ll='ls -la'" >> ~/.bashrc
source ~/.bashrc
# Functions in .bashrc
mkcd() {
mkdir -p "$1" && cd "$1"
}
extract() {
if [ -f $1 ] ; then
case $1 in
*.tar.bz2) tar xjf $1 ;;
*.tar.gz) tar xzf $1 ;;
*.bz2) bunzip2 $1 ;;
*.rar) unrar e $1 ;;
*.gz) gunzip $1 ;;
*.tar) tar xf $1 ;;
*.tbz2) tar xjf $1 ;;
*.tgz) tar xzf $1 ;;
*.zip) unzip $1 ;;
*.Z) uncompress $1 ;;
*.7z) 7z x $1 ;;
*) echo "'$1' cannot be extracted via extract()" ;;
esac
else
echo "'$1' is not a valid file"
fi
}
Conclusion
Bash is an incredibly powerful tool for system administration, development workflows, and automation. This guide covers the essential commands and concepts, but there's always more to learn:
Key Takeaways
- File Operations:
ls,cp,mv,rm,mkdirfor basic file management - Text Processing:
grep,sed,awk,cutfor manipulating text - Permissions:
chmod,chownfor access control - Process Management:
ps,kill,jobsfor controlling processes - Redirection:
>,>>,|for managing input/output - Scripting: Variables, conditionals, loops for automation
- System Info:
uname,df,freefor monitoring - Networking:
ssh,scp,curlfor network operations
Best Practices
- Use tab completion to save time and avoid typos
- Test commands with
-ior--interactivebefore destructive operations - Quote variables to handle spaces and special characters
- Use
set -ein scripts to exit on errors - Keep backups before using
rm -rf - Learn one command at a time and practice regularly
- Read man pages (
man command) for detailed information - Customize your environment with aliases and functions
- Use version control for important scripts
- Be careful with sudo - only use when necessary
Further Learning
man bash- Bash manualhelp- Built-in help for shell commands- Online resources: tldr.sh, explainshell.com
- Practice with real tasks and automation
- Study other shells (zsh, fish) for inspiration
Bash mastery comes with practice. Start with simple commands and gradually build up to complex scripts and automation tasks.
Complete Bash Exercises with Solutions
Practice Bash scripting with solved exercises to improve your command-line and scripting skills.
Link: https://macronepal.com/complete-bash-exercises-with-solutions/
Complete Guide to Bash Crontab Command
Learn how to schedule and automate tasks efficiently using the Bash crontab command.
Link: https://macronepal.com/complete-guide-to-bash-crontab-command-schedule-tasks/
Complete Guide to Bash Arrays
Understand how to create, manage, and use arrays in Bash scripting.
Link: https://macronepal.com/complete-guide-to-bash-arrays/
Bash Quiz: Test Your Knowledge
Test your Bash scripting knowledge with quizzes and practical questions.
Link: https://macronepal.com/bash-quiz-test-your-knowledge/
Complete Guide to Bash Functions
Learn how to write reusable Bash functions for cleaner and efficient scripts.
Link: https://macronepal.com/complete-guide-to-bash-functions/
Complete Guide to Bash Loops
Master loops in Bash for repetitive tasks and automation.
Link: https://macronepal.com/complete-guide-to-bash-loops/
Complete Guide to Bash If-Else Statements
Learn decision-making in Bash using conditional statements.
Link: https://macronepal.com/complete-guide-to-bash-ifelse-statements/
Complete Guide to Bash Operators
Explore arithmetic, logical, and comparison operators in Bash.
Link: https://macronepal.com/complete-guide-to-bash-operators/
Complete Guide to Bash Data Types
Understand variables and different data types used in Bash scripting.
Link: https://macronepal.com/complete-guide-to-bash-data-types/
Complete Guide to Bash Variables
Learn how to declare, assign, and use variables in Bash scripts.
Link: https://macronepal.com/complete-guide-to-bash-variables/
Complete Guide to Bash Scripting
A complete introduction to writing Bash scripts for automation.
Link: https://macronepal.com/complete-guide-to-bash-scripting/
Complete Guide to Basic Bash Syntax
Learn the fundamental syntax needed to write Bash commands and scripts.
Link: https://macronepal.com/complete-guide-to-basic-bash-syntax/
Complete Guide to Bash Chgrp Command
Learn how to change group ownership of files and directories.
Link: https://macronepal.com/complete-guide-to-bash-chgrp-command-change-group-ownership-2/
Complete Guide to Bash Chgrp Command (Alternate)
Another detailed explanation of Bash group ownership management.
Link: https://macronepal.com/complete-guide-to-bash-chgrp-command-change-group-ownership/
Complete Guide to Bash File Permissions and Ownership
Understand Linux file permissions and ownership management.
Link: https://macronepal.com/complete-guide-to-bash-file-permissions-and-ownership/
Complete Guide to Bash Chmod Command
Learn how to modify file permissions using chmod.
Link: https://macronepal.com/complete-guide-to-bash-chmod-command-change-file-permissions/
Complete Guide to Bash Chown Command
Change file ownership using the Bash chown command.
Link: https://macronepal.com/complete-guide-to-bash-chown-command-change-file-ownership/
Complete Guide to Bash SCP Command
Securely transfer files between systems using SCP.
Link: https://macronepal.com/complete-guide-to-bash-scp-command-secure-copy/
Complete Guide to Bash SSH Command
Learn secure remote access and server management using SSH.
Link: https://macronepal.com/complete-guide-to-bash-ssh-command/
Bash Wget Command Complete Guide
Download files from the internet using the wget command.
Link: https://macronepal.com/bash-wget-command-complete-guide-to-non-interactive-network-downloader/