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Bash-learning/Bash Cheat Sheet.md
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---
title: Bash Cheat Sheet
created: '2025-06-29T16:47:55.778Z'
modified: '2025-06-29T16:57:39.219Z'
---
# Bash Cheat Sheet
### A cheat sheet for bash commands.
>**Note** 💡<br>
> - A single hyphen `-` is used to represent a short option, such as `-a`.<br>
> - A double hyphen `--` is used to denote a long option, such as `--all`.<br>
> - Example command : `ls -a|--all` (List all directories). Can use either use the short or long options.
> - Both short and long options were incorporated for educational purposes, allowing users to choose the preferred format.<br>
> - It's important to note that not all commands have both short and long options. Some commands may only have short options, while others may only have long options.
### 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)
- [Sorting Files](#sorting-files)
- [File Permissions](#file-permissions)
- [Finding Files](#finding-files)
- [Find in Files](#find-in-files)
- [Replace in Files](#replace-in-files)
- [File Editor](#file-editor)
- [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 the previously chosen 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 -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|--follow 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)
## Sorting Files
```bash
sort foo.txt # Sort file (ascending order)
sort -r|--reverse foo.txt # Sort file (descending order)
sort -n|--numeric-sort foo.txt # Sort numbers instead of strings
sort -t|--field-separator: -k 3n /foo/foo.txt # Sort by the third column of a 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 -i|--in-place 's/fox/bear/g' foo.txt # Replace fox with bear and overwrite foo.txt
sed -i|--in-place '/red fox/i\blue bear' foo.txt # Insert blue bear before red fox and overwrite foo.txt
sed -i|--in-place '/red fox/a\blue bear' foo.txt # Insert blue bear after red fox and overwrite foo.txt
sed -i|--in-place '10s/find/replace/' foo.txt # Replace the 10th line of the file
sed -i|--in-place '10,20s/find/replace/' foo.txt # Replace in the file 10-20 lines
```
[⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents)
### File Editor
```bash
nano # Open a new file in nano
nano foo.txt # Open a specific file
nano -m|--mouse foo.txt # Enable the use of the mouse
nano -l|--linenumbers foo.txt # Show line numbers in front of the text
nano +line,10 foo.txt # Open file positioning the cursor at the specified line and column
nano -B|--backup foo.txt # Create a backup file (`foo~`) when saving edits
```
[⬆ 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
dpkg -P package_name.deb # Remove a deb file installion (including configuration files)
rpm -i|--install package_name.rpm # Install a rpm file installion
rpm -e package_name.rpm # Remove rpm file installion (including dependencies)
```
### 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 a file editor
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 a file editor to execute in 2 minutes
at 12:34 PM next month # Create a task in a file editor to execute at 12:34 PM next month
at tomorrow # Create a task in a file editor to execute tomorrow
```
[⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ](#contents)
## User Management
```bash
sudo su # Switch to root user
sudo foo # Execute commands(has permission denied) as the root user
sudo nano /foo/foo.txt # Open directories and files(is not writable) as the root user
su username # Switch to a different user
passwd # To change the password of a user
adduser username # To add a new 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 # Display information of all the users logged in
last username # Display information of a particular user
w # Display who is online
```
[⬆ 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
ifconfig # Display all network card and interface information
ifconfig -a # Display information of all network cards (including those that are not started at boot)
ifconfig eth0 # Display specific device information
ifconfig eth0 up # Turn on the network card
ifconfig eth0 down # Turn off the network card
ifconfig eth0 192.168.120.56 # Configure IP address for network card
curl ifconfig.me # Obtain external IP address
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
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
```bash
uname -s # Print kernel name
uname -r # Print kernel release
uname -m # Print Architecture
uname -o # Print Operating System
uname -a # Print all Systen info
lsb_release -a # Print distribution-specific information
dpkg --print-architecture # Print-architecture by name
cat /proc/cpuinfo # Show cpu info
cat /proc/meminfo # Show memory info
```
[⬆ 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 -S foo # Start a new named session
screen -ls # List all sessions
screen -R 31166 # Reattach to a session
exit # Exit a session
reset # Reset the terminal(when binary and the terminal state is messed up)
```
[⬆ 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)
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