Basic Commands:
- cd: Change directory
- Example:
cd Documents(Change to the “Documents” directory)
- Example:
- ls: List files and directories
- Example:
ls -l(List files and directories in long format)
- Example:
- pwd: Print working directory
- Example:
pwd(Display the current directory)
- Example:
- mkdir: Create a directory
- Example:
mkdir new_dir(Create a directory named “new_dir”)
- Example:
- rm: Remove files or directories
- Example:
rm file.txt(Remove a file named “file.txt”) - Example:
rm -r dir/(Remove a directory named “dir” and its contents)
- Example:
- cp: Copy files and directories
- Example:
cp file.txt new_file.txt(Copy “file.txt” to “new_file.txt”)
- Example:
- mv: Move or rename files and directories
- Example:
mv file.txt new_dir/(Move “file.txt” to “new_dir/”) - Example:
mv old_name.txt new_name.txt(Rename “old_name.txt” to “new_name.txt”)
- Example:
- cat: Concatenate and display file contents
- Example:
cat file.txt(Display the contents of “file.txt”)
- Example:
- touch: Create an empty file or update timestamp
- Example:
touch new_file.txt(Create an empty file named “new_file.txt”)
- Example:
- echo: Print a message or variable
- Example:
echo "Hello, World!"(Print the message “Hello, World!”) - Example:
echo $PATH(Print the value of the “PATH” environment variable)
- Example:
File Permissions:
- chmod: Change file permissions
- Example:
chmod +x script.sh(Grant execute permission to “script.sh”) - Example:
chmod 644 file.txt(Set read and write permissions for the owner, and read permissions for others on “file.txt”)
- Example:
- chown: Change file ownership
- Example:
chown user:group file.txt(Change the owner and group of “file.txt” to “user” and “group” respectively)
- Example:
File Manipulation:
- grep: Search for a pattern in files
- Example:
grep "pattern" file.txt(Search for “pattern” in “file.txt”)
- Example:
- sed: Stream editor for text manipulation
- Example:
sed 's/old/new/g' file.txt(Replace all occurrences of “old” with “new” in “file.txt”)
- Example:
- wc: Count lines, words, and characters in a file
- Example:
wc -l file.txt(Count the number of lines in “file.txt”)
- Example:
Scripting:
- Variables: Assign and use variables
- Example:
name="John"; echo "Hello, $name!"(Assign “John” to the variable “name” and print a message using the variable)
- Example:
- if-else: Conditional statements
- Example:
if [ $num -gt 10 ]; then echo "Greater than 10" else echo "Less than or equal to 10" fi(Check if the variable “num” is greater than 10 and print the appropriate message) - for loop: Iterate over a sequence
- Example:
for i in {1..5}; do echo "Number: $i" done(Iterate from 1 to 5 and print the number in each iteration)
- Example:
- while loop: Execute commands while a condition is true
- Example:
num=1 while [ $num -le 5 ]; do echo "Number: $num" num=$((num + 1)) done(Print numbers from 1 to 5 using a while loop)
- Example:
- Functions: Define and use functions
- Example:
greet() { echo "Hello, $1!" } greet "John"(Define a function called “greet” that takes a parameter and greets the person)
- Example:
- Command substitution: Use command output as a variable
- Example:
date=$(date +%Y-%m-%d) echo "Today's date is: $date"(Assign the current date to the variable “date” using command substitution)
- Example:
- Example:
Input and output redirection:
- Example:
command > output.txt(Redirect the output of a command to a file) - Pipes: Connect the output of one command to the input of another
- Example:
cat file.txt | grep "pattern"(Search for a pattern in the contents of a file using pipes)
- Example:
- Command line arguments: Access arguments passed to a script
- Example:
echo "The script name is: $0" echo "First argument: $1" echo "Second argument: $2"(Print the script name, along with the first and second arguments)
- Example:
Conditional Expressions:
- [[…]]: Extended test command with advanced conditionals
- Example:
if [[ $num -gt 10 && $num -lt 20 ]]; then echo "Number is between 10 and 20" fi(Check if the variable “num” is greater than 10 and less than 20)
- Example:
- case: Execute commands based on pattern matching
- Example:
case $option in "a") echo "Option A selected" ;; "b") echo "Option B selected" ;; *) echo "Invalid option" ;; esac(Execute different commands based on the value of the variable “option”)
- Example:
Command Line Tools:
- find: Search for files and directories in a directory hierarchy
- Example:
find . -name "*.txt"(Find all files with the extension “.txt” in the current directory and its subdirectories)
- Example:
- grep: Search for a pattern in files
- Example:
grep "pattern" file.txt(Search for the pattern “pattern” in the file “file.txt”)
- Example:
- awk: Text processing tool for extracting data and generating reports
- Example:bashCopy code
awk '{print $1}' file.txt(Print the first field of each line in “file.txt”)
- Example:bashCopy code
- sort: Sort lines of text files
- Example:
sort file.txt(Sort the lines in “file.txt” in ascending order)
- Example:
- cut: Extract specific columns from a file
- Example:
cut -d "," -f 1,3 file.csv(Extract the first and third columns from a CSV file, assuming comma as the delimiter)
- Example:
Shell Variables and Environment:
- $HOME: Home directory
- Example:
cd $HOME(Change to the user’s home directory)
- Example:
- $USER: Current user’s username
- Example:
echo "Hello, $USER!"(Print a personalized greeting for the current user)
- Example:
- $PATH: Colon-separated list of directories to search for executable files
- Example:
echo $PATH(Display the current value of the PATH variable)
- Example:
File Compression and Archiving:
- tar: Archive files into a tarball
- Example:
tar -cvf archive.tar file1.txt file2.txt(Create a tarball named “archive.tar” containing “file1.txt” and “file2.txt”)
- Example:
- gzip: Compress files using the gzip algorithm
- Example:
gzip file.txt(Compress “file.txt” and create “file.txt.gz”)
- Example:
- gunzip: Decompress gzip files
- Example:
gunzip file.txt.gz(Decompress “file.txt.gz” and restore the original “file.txt”)
- Example:
Process Management:
- ps: Report a snapshot of current processes
- Example:
ps aux(Display a detailed list of all running processes)
- Example:
- kill: Terminate a process by its process ID (PID)
- Example:
kill 1234(Terminate the process with PID 1234)
- Example:
- top: Monitor system processes in real-time
- Example:
top(Display the current CPU and memory usage, along with the list of processes)
- Example:
- bg: Move a suspended process to the background
- Example:
sleep 10 # Press Ctrl + Z to suspend the process bg # Move the suspended process to the background
- Example:
- fg: Bring a background process to the foreground
- Example:
sleep 10 & # Start a process in the background fg # Bring the background process to the foreground
- Example:
Text Manipulation:
- tr: Translate or delete characters
- Example:
echo "Hello" | tr 'el' 'XY'(Translate ‘e’ to ‘X’ and ‘l’ to ‘Y’ in the word “Hello”)
- Example:
- head: Output the first part of files
- Example:
head -n 5 file.txt(Display the first 5 lines of “file.txt”)
- Example:
- tail: Output the last part of files
- Example:
tail -n 10 file.txt(Display the last 10 lines of “file.txt”)
- Example:
- sort: Sort lines of text files
- Example:
sort file.txt(Sort the lines of “file.txt” in lexicographic order)
- Example:
- uniq: Report or omit repeated lines
- Example:
uniq file.txt(Remove consecutive duplicate lines from “file.txt”)
- Example:
Networking:
- ping: Send ICMP echo requests to a network host
- Example:
ping google.com(Send ICMP echo requests to “google.com”)
- Example:
- ifconfig: Configure and display network interface parameters
- Example:
ifconfig eth0(Display details of the “eth0” network interface)
- Example:
- ssh: Securely connect to a remote machine
- Example:
ssh user@hostname(Establish an SSH connection to “hostname” as “user”)
- Example:
- Job Control:
- jobs: List active jobs and their status
- Example:
jobs(Display a list of currently running jobs)
- Example:
- Ctrl + C: Interrupt the current foreground process
- Example: Pressing Ctrl + C in the terminal terminates the currently running command
- Ctrl + Z: Suspend the current foreground process
- Example: Pressing Ctrl + Z in the terminal suspends the currently running command
- nohup: Run a command immune to hangups, even if the terminal is closed
- Example:
nohup command &(Run “command” in the background, ignoring hangup signals)
- Example:
Environment Variables:
- export: Set an environment variable
- Example:
export VAR_NAME=value(Set the environment variable “VAR_NAME” with the value “value”)
- Example:
- $PATH: Environment variable containing the directories to search for executable files
- Example:
echo $PATH(Display the current value of the PATH variable)
- Example:
- $HOME: Environment variable representing the user’s home directory
- Example:
cd $HOME(Change to the user’s home directory)
- Example:
Process Control:
- &: Run a command in the background
- Example:
command &(Run “command” in the background)
- Example:
- ctrl+z: Suspend the current foreground process
- Example: Pressing Ctrl + Z in the terminal suspends the currently running command
- jobs: List active jobs and their status
- Example:
jobs(Display a list of currently running jobs)
- Example:
- fg: Bring a background process to the foreground
- Example:
fg %1(Bring the first background job to the foreground)
- Example:
- bg: Resume a suspended background process
- Example:
bg %1(Resume the first suspended background job)
- Example:
Shell Scripting:
- #!/bin/bash: Shebang line specifying the shell to execute the script
- Example:
#!/bin/bash(Place this line at the beginning of a script to specify Bash as the interpreter)
- Example:
- $0: Special variable representing the script’s name
- Example:
echo "Script name: $0"(Print the name of the script)
- Example:
- $1, $2, …: Positional parameters representing command-line arguments
- Example:
echo "First argument: $1"(Print the first command-line argument)
- Example:
- $@: All the command-line arguments as separate strings
- Example:
for arg in "$@"; do echo "Argument: $arg"; done(Print all command-line arguments)
- Example:
- $#: Number of command-line arguments
- Example:
echo "Number of arguments: $#"
- Example:
Input and Output:
- stdin, stdout, stderr: Standard input, output, and error streams
- Example:
command < input.txt(Redirect the contents of “input.txt” as input to the command) - Example:
command > output.txt(Redirect the command’s output to “output.txt”) - Example:
command 2> error.txt(Redirect the command’s error output to “error.txt”)
- Example:
- tee: Read from standard input and write to standard output and files
- Example:
command | tee output.txt(Pass the output of “command” to both the standard output and “output.txt”)
- Example:
System Information:
- uname: Print system information
- Example:
uname -a(Print all system information, including the kernel version)
- Example:
- uptime: Display system uptime and load average
- Example:
uptime(Display the system’s uptime and load average)
- Example:
- free: Display memory usage
- Example:
free -h(Display memory usage in a human-readable format)
- Example:
- df: Report file system disk space usage
- Example:
df -h(Display disk space usage in a human-readable format)
- Example:
Process Monitoring:
- ps: Report a snapshot of current processes
- Example:
ps aux(Display a detailed list of all running processes)
- Example:
- top: Monitor system processes in real-time
- Example:
top(Display the current CPU and memory usage, along with the list of processes)
- Example:
- htop: Interactive process viewer (requires installation)
- Example:
htop(Launch the interactive process viewer)
- Example:
- File Searching:
- locate: Find files by name
- Example:
locate myfile.txt(Find the file named “myfile.txt” on the system)
- Example:
- find: Search for files and directories based on various criteria
- Example:
find /path/to/search -name "*.txt"(Find all files with the extension “.txt” in the specified directory and its subdirectories)
- Example:
- Network Operations:
- curl: Transfer data from or to a server
- Example:
curl http://example.com(Retrieve the content of a web page)
- Example:
- wget: Download files from the web
- Example:
wget http://example.com/file.txt(Download the file “file.txt” from a web server)
- Example:
Conditional Execution:
- &&: Execute the next command if the previous command succeeds
- Example:
command1 && command2(Run “command2” only if “command1” succeeds)
- Example:
- ||: Execute the next command if the previous command fails
- Example:
command1 || command2(Run “command2” only if “command1” fails)
- Example:
Command Substitution:
- $(command): Substitute the output of a command
- Example:
echo "Today is $(date)"(Print the current date using the “date” command)
- Example:
command: (Backticks) Substitute the output of a command (older syntax)- Example:
echo "Today isdate"(Print the current date using the “date” command)
- Example:
Advanced Bash Scripting:
- Arrays: Store multiple values in a single variable
- Example:
my_array=("value1" "value2" "value3") echo "${my_array[0]}" # Access the first element echo "${my_array[@]}" # Print all elements
- Example:
Command History:
- history: Display a list of previously executed commands
- Example:
history(Display a list of recently executed commands)
- Example:
- !!: Repeat the last executed command
- Example:
!!(Execute the last command again)
- Example:
- !n: Repeat the nth command in the history
- Example:
!42(Execute the 42nd command in the history)
- Example:
- !string: Repeat the most recent command starting with “string”
- Example:
!ls(Execute the most recent command starting with “ls”)
- Example:
Debugging and Profiling:
- set -x: Enable debugging mode
- Example:
set -x(Enable debugging mode, displaying each command before executing it)
- Example:
- strace: Trace system calls and signals
- Example:
strace command(Trace system calls made by “command”)
- Example:
- time: Measure the execution time of a command
- Example:
time command(Measure the execution time of “command”)
- Example:
