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Credits: fossbytes.com [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ](#table)

>**Note**
> Examples like `-a|--all` option flags means, single `-` used for _short_ option(-a) **or**| double `--` used for _long_ option(--all). Both was added for educational purpose. ### Contents - [Command Information](#command-information) - [Command History](#command-history) - [Navigating Directories](#navigating-directories) - [Creating Directories](#creating-directories) - [Moving Directories](#moving-directories) - [Deleting Directories](#deleting-directories) - [Creating Files](#creating-files) - [Standard Output, Error and Input](#standard-output-standard-error-and-standard-input) - [Moving Files](#moving-files) - [Deleting Files](#deleting-files) - [Reading Files](#reading-files) - [File Permissions](#file-permissions) - [Finding Files](#finding-files) - [Find in Files](#find-in-files) - [Replace in Files](#replace-in-files) - [Symbolic Links](#symbolic-links) - [Compressing Files](#compressing-files) - [Decompressing Files](#decompressing-files) - [Packages](#packages) - [Disk Usage](#disk-usage) - [Memory Usage](#memory-usage) - [Shutdown and Reboot](#shutdown-and-reboot) - [Identifying Processes](#identifying-processes) - [Process Priority](#process-priority) - [Killing Processes](#killing-processes) - [Date & Time](#date--time) - [Scheduled Tasks](#scheduled-tasks) - [User Mangement](#user-management) - [HTTP Requests](#http-requests) - [Network Troubleshooting](#network-troubleshooting) - [DNS](#dns) - [Hardware](#hardware) - [System Information](#system-information) - [Terminal Multiplexers](#terminal-multiplexers) - [Secure Shell Protocol (SSH)](#secure-shell-protocol-ssh) - [Secure Copy](#secure-copy) - [Bash Profile](#bash-profile) - [Bash Script](#bash-script) # ## Command Information ```bash man chmod # Display page manual of a command man -f|--whatis chmod # Display short description about a command man -k|--apropos permission # Display all related commands from a specific keyword chmod --help # Display usage options of a command ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Command History ```bash history # View all previous commands history | grep foo # View the commands using a specific word history | grep -E|--extended-regexp -i|--ignore-case 'foo1|foo2|foo3' # View the commands using more than 1 specific word(case sensitive) history | head -n|--lines 3 # View the first 3 executed commands history 3 # View the last 3 executed commands history -d 99 # Clear a command from a specific line history -c # Clears all history commands !! # Run the last command executed touch foo.sh # <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<┐ chmod +x !$ # !$ is the last argument of the last command i.e. foo.sh <<<<┘ ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Navigating Directories ```bash pwd # Print current directory path ls # List directories ls -a|--all # List directories including hidden ls -l # List directories in long form ls -l -h|--human-readable # List directories in long form with human readable sizes ls -t # List directories by modification time, newest first stat foo.txt # List size, created and modified timestamps for a file stat foo # List size, created and modified timestamps for a directory tree # List directory and file tree tree -a # List directory and file tree including hidden tree -d # List directory tree cd foo # Go to foo sub-directory cd # Go to home directory cd ~ # Go to home directory cd - # Go to last directory pushd foo # Go to foo sub-directory and add previous directory to stack popd # Go back to directory in stack saved by `pushd` ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Creating Directories ```bash mkdir foo # Create a directory mkdir foo bar # Create multiple directories mkdir -p|--parents foo/bar # Create nested directory mkdir -p|--parents {foo,bar}/baz # Create multiple nested directories mktemp -d|--directory # Create a temporary directory ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Moving Directories ```bash cp -R|--recursive foo bar # Copy directory mv foo bar # Move directory rsync -z|--compress -v|--verbose /foo /bar # Copy directory, overwrites destination rsync --ignore-existing -a|--archive-a|--archive -z|--compress -v|--verbose /foo /bar # Copy directory, without overwriting destination rsync -avz /foo username@hostname:/bar # Copy local directory to remote directory rsync -avz username@hostname:/foo /bar # Copy remote directory to local directory ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Deleting Directories ```bash rmdir foo # Delete non-empty directory rm -r|--recursive foo # Delete directory including contents rm -r|--recursive -f|--force foo # Delete directory including contents, ignore nonexistent files and never prompt ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Creating Files ```bash touch foo.txt # Create file or update existing files modified timestamp touch foo.txt bar.txt # Create multiple files touch {foo,bar}.txt # Create multiple files touch test{1..3} # Create test1, test2 and test3 files touch test{a..c} # Create testa, testb and testc files mktemp # Create a temporary file ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Standard Output, Standard Error and Standard Input ```bash echo "foo" > bar.txt # Overwrite file with content echo "foo" >> bar.txt # Append to file with content ls exists 1> stdout.txt # Redirect the standard output to a file ls noexist 2> stderror.txt # Redirect the standard error output to a file ls > out.txt 2>&1 # Redirect standard output and error to a file ls > /dev/null # Discard standard output and error read foo # Read from standard input and write to the variable foo ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Moving Files ```bash cp foo.txt bar.txt # Copy file mv foo.txt bar.txt # Move file rsync -z|--compress -v|--verbose /foo.txt /bar # Copy file quickly if not changed rsync -z|--compress -v|--verbose /foo.txt /bar.txt # Copy and rename file quickly if not changed ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Deleting Files ```bash rm foo.txt # Delete file rm -f|--force foo.txt # Delete file, ignore nonexistent files and never prompt ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Reading Files ```bash cat foo.txt # Print all contents less foo.txt # Print some contents at a time (g - go to top of file, SHIFT+g, go to bottom of file, /foo to search for 'foo') head foo.txt # Print top 10 lines of file tail foo.txt # Print bottom 10 lines of file tail -f foo.txt # Print bottom 10 lines of file updating with new data open foo.txt # Open file in the default editor wc foo.txt # List number of lines words and characters in the file ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## File Permissions | # | Permission | rwx | Binary | | - | - | - | - | | 7 | read, write and execute | rwx | 111 | | 6 | read and write | rw- | 110 | | 5 | read and execute | r-x | 101 | | 4 | read only | r-- | 100 | | 3 | write and execute | -wx | 011 | | 2 | write only | -w- | 010 | | 1 | execute only | --x | 001 | | 0 | none | --- | 000 | For a directory, execute means you can enter a directory. | User | Group | Others | Description | | - | - | - | - | | 6 | 4 | 4 | User can read and write, everyone else can read (Default file permissions) | | 7 | 5 | 5 | User can read, write and execute, everyone else can read and execute (Default directory permissions) | - u - User - g - Group - o - Others - a - All of the above ```bash ls -l /foo.sh # List file permissions chmod +100 foo.sh # Add 1 to the user permission chmod -100 foo.sh # Subtract 1 from the user permission chmod u+x foo.sh # Give the user execute permission chmod g+x foo.sh # Give the group execute permission chmod u-x,g-x foo.sh # Take away the user and group execute permission chmod u+x,g+x,o+x foo.sh # Give everybody execute permission chmod a+x foo.sh # Give everybody execute permission chmod +x foo.sh # Give everybody execute permission ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Finding Files Find binary files for a command. ```bash type -a wget # Display all locations of executable which -a wget # Display all locations of executables whereis wget # Find the binary, source, and manual page files ``` `locate` uses an index and is fast. ```bash updatedb # Update the index locate foo.txt # Find a file locate --ignore-case # Find a file and ignore case locate f*.txt # Find a text file starting with 'f' ``` `find` doesn't use an index and is slow. ```bash find /path -name foo.txt # Find a file find /path -iname foo.txt # Find a file with case insensitive search find /path -name "*.txt" # Find all text files find /path -name foo.txt -delete # Find a file and delete it find /path -name "*.png" -exec pngquant {} # Find all .png files and execute pngquant on it find /path -type f -name foo.txt # Find a file find /path -type d -name foo # Find a directory find /path -type l -name foo.txt # Find a symbolic link find /path -type f -mtime +30 # Find files that haven't been modified in 30 days find /path -type f -mtime +30 -delete # Delete files that haven't been modified in 30 days ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Find in Files ```bash grep 'foo' /bar.txt # Search for 'foo' in file 'bar.txt' grep 'foo' /bar -r|--recursive # Search for 'foo' in directory 'bar' grep 'foo' /bar -R|--dereference-recursive # Search for 'foo' in directory 'bar' and follow symbolic links grep 'foo' /bar -l|--files-with-matches # Show only files that match grep 'foo' /bar -L|--files-without-match # Show only files that don't match grep 'Foo' /bar -i|--ignore-case # Case insensitive search grep 'foo' /bar -x|--line-regexp # Match the entire line grep 'foo' /bar -C|--context 1 # Add N line of context above and below each search result grep 'foo' /bar -v|--invert-match # Show only lines that don't match grep 'foo' /bar -c|--count # Count the number lines that match grep 'foo' /bar -n|--line-number # Add line numbers grep 'foo' /bar --colour # Add colour to output grep 'foo\|bar' /baz -R # Search for 'foo' or 'bar' in directory 'baz' grep --extended-regexp|-E 'foo|bar' /baz -R # Use regular expressions grep -E 'foo|bar' /baz -R # Use regular expressions ``` ### Replace in Files ```bash sed 's/fox/bear/g' foo.txt # Replace fox with bear in foo.txt and output to console sed 's/fox/bear/gi' foo.txt # Replace fox (case insensitive) with bear in foo.txt and output to console sed 's/red fox/blue bear/g' foo.txt # Replace red with blue and fox with bear in foo.txt and output to console sed 's/fox/bear/g' foo.txt > bar.txt # Replace fox with bear in foo.txt and save in bar.txt sed 's/fox/bear/g' foo.txt -i|--in-place # Replace fox with bear and overwrite foo.txt ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Symbolic Links ```bash ln -s|--symbolic foo bar # Create a link 'bar' to the 'foo' folder ln -s|--symbolic -f|--force foo bar # Overwrite an existing symbolic link 'bar' ls -l # Show where symbolic links are pointing ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Compressing Files ### zip Compresses one or more files into *.zip files. ```bash zip foo.zip /bar.txt # Compress bar.txt into foo.zip zip foo.zip /bar.txt /baz.txt # Compress bar.txt and baz.txt into foo.zip zip foo.zip /{bar,baz}.txt # Compress bar.txt and baz.txt into foo.zip zip -r|--recurse-paths foo.zip /bar # Compress directory bar into foo.zip ``` ### gzip Compresses a single file into *.gz files. ```bash gzip /bar.txt foo.gz # Compress bar.txt into foo.gz and then delete bar.txt gzip -k|--keep /bar.txt foo.gz # Compress bar.txt into foo.gz ``` ### tar -c Compresses (optionally) and combines one or more files into a single *.tar, *.tar.gz, *.tpz or *.tgz file. ```bash tar -c|--create -z|--gzip -f|--file=foo.tgz /bar.txt /baz.txt # Compress bar.txt and baz.txt into foo.tgz tar -c|--create -z|--gzip -f|--file=foo.tgz /{bar,baz}.txt # Compress bar.txt and baz.txt into foo.tgz tar -c|--create -z|--gzip -f|--file=foo.tgz /bar # Compress directory bar into foo.tgz ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Decompressing Files ### unzip ```bash unzip foo.zip # Unzip foo.zip into current directory ``` ### gunzip ```bash gunzip foo.gz # Unzip foo.gz into current directory and delete foo.gz gunzip -k|--keep foo.gz # Unzip foo.gz into current directory ``` ### tar -x ```bash tar -x|--extract -z|--gzip -f|--file=foo.tar.gz # Un-compress foo.tar.gz into current directory tar -x|--extract -f|--file=foo.tar # Un-combine foo.tar into current directory ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Packages ```bash apt update # Refreshes repository index apt search wget # Search for a package apt show wget # List information about the wget package apt list --all-versions wget # List all versions of the package apt install wget # Install the latest version of the wget package apt install wget=1.2.3 # Install a specific version of the wget package apt remove wget # Removes the wget package apt upgrade # Upgrades all upgradable packages apt clean # Clears out the local repository of downloaded package files dpkg -i|--install package_name.deb # Install deb file rpm -i|--install package_name.rpm # Install rpm file ``` ### Install package source code ```bash tar zxvf sourcecode.tar.gz cd sourcecode ./configure make make install ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Disk Usage ```bash df # List disks, size, used and available space df -h|--human-readable # List disks, size, used and available space in a human readable format du # List current directory, subdirectories and file sizes du /foo/bar # List specified directory, subdirectories and file sizes du -h|--human-readable # List current directory, subdirectories and file sizes in a human readable format du -d|--max-depth # List current directory, subdirectories and file sizes within the max depth du -d 0 # List current directory size ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Memory Usage ```bash free # Show memory usage free -h|--human # Show human readable memory usage free -h|--human --si # Show human readable memory usage in power of 1000 instead of 1024 free -s|--seconds 5 # Show memory usage and update continuously every five seconds ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Shutdown and Reboot ```bash shutdown # Shutdown in 1 minute shutdown now # Immediately shut down shutdown +5 # Shutdown in 5 minutes shutdown -r|--reboot # Reboot in 1 minute shutdown -r|--reboot now # Immediately reboot shutdown -r|--reboot +5 # Reboot in 5 minutes shutdown -c # Cancel a shutdown or reboot reboot # Reboot now reboot -f # Force a reboot ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Identifying Processes ```bash top # List all processes interactively htop # List all processes interactively ps ax # List all processes pidof foo # Return the PID of all foo processes CTRL+Z # Suspend a process running in the foreground bg # Resume a suspended process and run in the background fg # Bring the last background process to the foreground fg 1 # Bring the background process with the PID to the foreground sleep 30 & # Sleep for 30 seconds and move the process into the background jobs # List all background jobs jobs -p # List all background jobs with their PID lsof # List all open files and the process using them lsof -itcp:4000 # Return the process listening on port 4000 ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Process Priority Process priorities go from -20 (highest) to 19 (lowest). ```bash nice -n -20 foo # Change process priority by name renice 20 PID # Change process priority by PID ps -o ni PID # Return the process priority of PID ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Killing Processes ```bash CTRL+C # Kill a process running in the foreground kill PID # Shut down process by PID gracefully. Sends TERM signal. kill -9 PID # Force shut down of process by PID. Sends SIGKILL signal. pkill foo # Shut down process by name gracefully. Sends TERM signal. pkill -9 foo # force shut down process by name. Sends SIGKILL signal. killall foo # Kill all process with the specified name gracefully. ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Date & Time ```bash date # Print the date and time date --iso-8601 # Print the ISO8601 date date --iso-8601=ns # Print the ISO8601 date and time date -s "02 DEC 2020 12:02:02" # Manually change date and time dpkg-reconfigure tzdata # Change date/timezone uptime # Print how long the system has been running time tree # Print amount of time to tree takes to execute ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Scheduled Tasks ```pre * * * * * Minute, Hour, Day of month, Month, Day of the week ``` ```bash crontab -l # List cron tab crontab -e # Edit cron tab in Vim crontab /path/crontab # Load cron tab from a file crontab -l > /path/crontab # Save cron tab to a file * * * * * foo # Run foo every minute */15 * * * * foo # Run foo every 15 minutes 0 * * * * foo # Run foo every hour 15 6 * * * foo # Run foo daily at 6:15 AM 44 4 * * 5 foo # Run foo every Friday at 4:44 AM 0 0 1 * * foo # Run foo at midnight on the first of the month 0 0 1 1 * foo # Run foo at midnight on the first of the year at -l # List scheduled tasks at -c 1 # Show task with ID 1 at -r 1 # Remove task with ID 1 at now + 2 minutes # Create a task in Vim to execute in 2 minutes at 12:34 PM next month # Create a task in Vim to execute at 12:34 PM next month at tomorrow # Create a task in Vim to execute tomorrow ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## User Management ```bash adduser username # To add a new user passwd -l|--lock username # To change the password of a user userdel username # To remove user userdel -r|--remove username # To remove user with home directory and mail spool usermod -a|--append -G|--groups GROUPNAME USERNAME # To add a user to a group deluser USER GROUPNAME # To remove a user from a group last # Shows information of all the users logged in last username # Gives information of a particular user ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## HTTP Requests ```bash curl https://example.com # Return response body curl -i|--include https://example.com # Include status code and HTTP headers curl -L|--location https://example.com # Follow redirects curl -O|--remote-name foo.txt https://example.com # Output to a text file curl -H|--header "User-Agent: Foo" https://example.com # Add a HTTP header curl -X|--request POST -H "Content-Type: application/json" -d|--data '{"foo":"bar"}' https://example.com # POST JSON curl -X POST -H --data-urlencode foo="bar" http://example.com # POST URL Form Encoded wget https://example.com/file.txt # Download a file to the current directory wget -O|--output-document foo.txt https://example.com/file.txt # Output to a file with the specified name ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Network Troubleshooting ```bash ping example.com # Send multiple ping requests using the ICMP protocol ping -c 10 -i 5 example.com # Make 10 attempts, 5 seconds apart ip addr # List IP addresses on the system ip route show # Show IP addresses to router curl ifconfig.me # Obtain external IP address netstat -i|--interfaces # List all network interfaces and in/out usage netstat -l|--listening # List all open ports traceroute example.com # List all servers the network traffic goes through mtr -w|--report-wide example.com # Continually list all servers the network traffic goes through mtr -r|--report -w|--report-wide -c|--report-cycles 100 example.com # Output a report that lists network traffic 100 times nmap 0.0.0.0 # Scan for the 1000 most common open ports on localhost nmap 0.0.0.0 -p1-65535 # Scan for open ports on localhost between 1 and 65535 nmap 192.168.4.3 # Scan for the 1000 most common open ports on a remote IP address nmap -sP 192.168.1.1/24 # Discover all machines on the network by ping'ing them ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## DNS ```bash dig example.com # Show query information of domain A records dig -4 example.com # Show IPv4 A records dig -6 example.com # Show IPv6 AAA records dig example.com @nameserver # Show query of a specific nameserver dig example.com -p 123 # Show query of a specific port number cat /etc/resolv.conf # Nameservers file cat /etc/systemd/resolved.conf # DNS resolver config file ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Hardware ```bash lsusb # List USB devices lspci # List PCI hardware lshw # List all hardware ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## System Information ``` uname -s # Print kernel name uname -r # Print kernel release uname -m # Print Architecture uname -o # Print Operating System ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Terminal Multiplexers Start multiple terminal sessions. Active sessions persist reboots. `tmux` is more modern than `screen`. ```bash tmux # Start a new session (CTRL-b + d to detach) tmux ls # List all sessions tmux attach -t 0 # Reattach to a session screen # Start a new session (CTRL-a + d to detach) screen -ls # List all sessions screen -R 31166 # Reattach to a session exit # Exit a session ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Secure Shell Protocol (SSH) ```bash ssh hostname # Connect to hostname using your current user name over the default SSH port 22 ssh -i foo.pem hostname # Connect to hostname using the identity file ssh user@hostname # Connect to hostname using the user over the default SSH port 22 ssh user@hostname -p 8765 # Connect to hostname using the user over a custom port ssh ssh://user@hostname:8765 # Connect to hostname using the user over a custom port ``` Set default user and port in `~/.ssh/config`, so you can just enter the name next time: ```bash $ cat ~/.ssh/config Host name User foo Hostname 127.0.0.1 Port 8765 $ ssh name ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Secure Copy ```bash scp foo.txt ubuntu@hostname:/home/ubuntu # Copy foo.txt into the specified remote directory scp ubuntu@hostname:/home/ubuntu/foo.txt /C:\Users\Admin # Copy foo.txt from the specified remote directory ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Bash Profile - bash - `.bashrc` - zsh - `.zshrc` ```bash # Always run ls after cd function cd { builtin cd "$@" && ls } # Prompt user before overwriting any files alias cp='cp --interactive' alias mv='mv --interactive' alias rm='rm --interactive' # Always show disk usage in a human readable format alias df='df -h' alias du='du -h' ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents) ## Bash Script ### Variables ```bash #!/bin/bash foo=123 # Initialize variable foo with 123 declare -i foo=123 # Initialize an integer foo with 123 declare -r foo=123 # Initialize readonly variable foo with 123 echo $foo # Print variable foo echo ${foo}_'bar' # Print variable foo followed by _bar echo ${foo:-'default'} # Print variable foo if it exists otherwise print default export foo # Make foo available to child processes unset foo # Make foo unavailable to child processes and current session ``` ### Environment Variables ```bash #!/bin/bash set # List all environment variables echo $PATH # Print PATH environment variable export FOO=Bar # Set an environment variable ``` ### Functions ```bash #!/bin/bash greet() { local world="World" echo "$1 $world" return "$1 $world" } greet "Hello" greeting=$(greet "Hello") ``` ### Exit Codes ```bash #!/bin/bash exit 0 # Exit the script successfully exit 1 # Exit the script unsuccessfully echo $? # Print the last exit code ``` ### Conditional Statements #### Boolean Operators - `$foo` - Is true - `!$foo` - Is false #### Numeric Operators - `-eq` - Equals - `-ne` - Not equals - `-gt` - Greater than - `-ge` - Greater than or equal to - `-lt` - Less than - `-le` - Less than or equal to - `-e` foo.txt - Check file exists - `-z` foo - Check if variable exists #### String Operators - `=` - Equals - `==` - Equals - `-z` - Is null - `-n` - Is not null - `<` - Is less than in ASCII alphabetical order - `>` - Is greater than in ASCII alphabetical order #### If Statements ```bash #!/bin/bash [[ if [[$foo = 'bar']]; then echo 'one' elif [[$foo = 'bar']] || [[$foo = 'baz']]; then echo 'two' elif [[$foo = 'ban']] && [[$USER = 'bat']]; then echo 'three' else echo 'four' fi ]] ``` #### Inline If Statements ```bash #!/bin/bash [[ $USER = 'rehan' ]] && echo 'yes' || echo 'no' ``` #### While Loops ```bash #!/bin/bash [ declare -i counter counter=10 while [$counter -gt 2]; do echo The counter is $counter counter=counter-1 done ] ``` #### For Loops ```bash #!/bin/bash for i in {0..10..2} do echo "Index: $i" done for filename in file1 file2 file3 do echo "Content: " >> $filename done for filename in *; do echo "Content: " >> $filename done ``` #### Case Statements ```bash #!/bin/bash echo "What's the weather like tomorrow?" read weather case $weather in sunny | warm ) echo "Nice weather: " $weather ;; cloudy | cool ) echo "Not bad weather: " $weather ;; rainy | cold ) echo "Terrible weather: " $weather ;; * ) echo "Don't understand" ;; esac ``` [⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents)

Char.	Description
~	Home directory [tilde]. The path to a user's home directory location.
-	Previous directory [dash]. Go back to previous directory.
/	Filename path separator [forward slash]. Separates the components of a filename. It also represents the path to root directory.
\	Escape [backslash]. A quoting mechanism for single characters. It preserves the literal value of the next character that follows, with the exception of newline.
│	Pipe. It passes the output (stdout) of a previous command to the input (stdin) of the next one, or to the shell. This is a method of chaining commands together.
||	The OR operator is used to chain commands. It will execute succeeded commands which follows and stops if the preceding command fails.
&&	The AND operator is used to chain commands. It will execute commands only if the first command is successful
;	Command separator [semicolon]. Used to separate multiple commands and execute all the ones that is successful.
&	Run job in background[and]. A command followed by an & will run in the background.
#	Comment [number sign]. Lines in files beginning with a # (with the exception of #!) are comments and will not be executed.
>, >>, <	Redirect a command's output or input into a file.
>|	Force redirection (even if the noclobber option is set). This will forcibly overwrite an existing file.
""	Double quotes protects the text inside them from being split into multiple words or arguments, yet allow substitutions to occur, meaning most other special characters is usually prevented.
' '	Single quotes protects the text inside them so that it has a literal meaning. This is a stronger form of quoting than double quotes.
" "	Whitespace. This is a tab, newline, vertical tab, form feed, carriage return, or space. Bash uses whitespace to determine where words begin and end.
:	Null command [colon]. This is the shell equivalent of a "NOP" (no op, a do-nothing operation). It may be considered a synonym for the shell builtin true.
!	Reverse (or negate) [exclamation]. The ! operator inverts the exit status of the command to which it is applied. It also inverts the meaning of a test operator.
*	Wild card [asterisk]. The * character serves as a "wild card" for filename expansion in globbing. By itself, it matches every filename in a given directory.
?	Wild card [question mark]. The ? character serves as a single-character "wild card" for filename expansion in globbing, as well as representing one character in an extended regular expression.
{ }	Inline group [curly brackets]. Commands inside the curly braces are treated as if they were one command. It is convenient to use these when Bash syntax requires only one command and a function doesn't feel warranted.
( )	Subshell group [bracket].Commands within are executed in a subshell (a new process) Used much like a sandbox, if a command causes side effects (like changing variables), it will have no effect on the current shell.
[ ]	Test expression between [ ]. It is part of the shell builtin test.
[[ ]]	Test expression between [[ ]]. It is more flexible than the single-bracket [ ] test.
(( ))	Integer expansion. Expand and evaluate integer expression.
;;	Terminator in a case option [double semicolon].
,, ,	Lowercase conversion in parameter substitution.
^, ^^	Uppercase conversion in parameter substitution.

| Key | Function | | :--: | :-- | | Ctrl+a | Moves cursor to beginning of text in line | | Ctrl+e | Moves cursor to end of text in line | | Ctrl+b | Moves cursor backward one character position | | Ctrl+f | Moves cursor forward one character position | | Ctrl+p | Fetch previous command from history list | | Ctrl+n | Fetch next command from history list | | Ctrl+d | Erase characters from cursor left to right | | Ctrl+u | Erase a line of input from cursor right to left of line | | Ctrl+k | Erase a line of input from cursor left to right of line | | Ctrl+w | Erase backwards to first non-alphanumeric character or empty space | | Ctrl+y | Fetch back command previously erased | | Ctrl+t | Reverses the position of the character the cursor is on with the previous character | | Ctrl+r | Reverse search commands from history list | | Ctrl+z | Pauses a foreground job | | Ctrl+c | Break/Terminate a foreground job | | Ctrl+o | Accept the current line for execution and fetch the next command | | Ctrl+l | Clear screen contents (command line needs to be empty) | | Ctrl+s | Suspend | | Ctrl+q | Resume | | Ctrl+d | Log out from a shell (similar to exit) |