A to Z command list

Note 💡
Use Ctrl+f to search keywords in desktop browsers, for mobile go to menu > find in page.

A

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

B

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C

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D

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

E

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

F

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

G

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

H

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

I

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

J

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

K

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

L

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

M

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N

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O

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P

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Q

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R

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

S

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T

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U

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

V

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W

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X

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Y

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Z

Credits: fossbytes & geeksforgeeks

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

Quick cheatsheet

Note 💡

• A single hyphen - is used to represent a short option, such as -a.
  
• A double hyphen -- is used to denote a long option, such as --all.
  
• 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.
  
• 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 History
• Navigating Directories
• Creating Directories
• Moving Directories
• Deleting Directories
• Creating Files
• Standard Output, Error and Input
• Moving Files
• Deleting Files
• Reading Files
• Sorting Files
• File Permissions
• Finding Files
• Find in Files
• Replace in Files
• File Editor
• Symbolic Links
• Compressing Files
• Decompressing Files
• Packages
• Disk Usage
• Memory Usage
• Shutdown and Reboot
• Identifying Processes
• Process Priority
• Killing Processes
• Date & Time
• Scheduled Tasks
• User Mangement
• HTTP Requests
• Network Troubleshooting
• DNS
• Hardware
• System Information
• Terminal Multiplexers
• Secure Shell Protocol (SSH)
• Secure Copy
• Bash Profile
• Bash Script

Command Information

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

Command History

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

Navigating Directories

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

Creating Directories

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

Moving Directories

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

Deleting Directories

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

Creating Files

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

Standard Output, Standard Error and Standard Input

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

Moving Files

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

Deleting Files

rm foo.txt            # Delete file
rm -f|--force foo.txt # Delete file, ignore nonexistent files and never prompt

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Reading Files

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

Sorting Files

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

File Permissions

For a directory, execute means you can enter a directory.

• u - User
• g - Group
• o - Others
• a - All of the above

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

Finding Files

Find binary files for a command.

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.

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.

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

Find in Files

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

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

File Editor

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

Symbolic Links

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

Compressing Files

zip

Compresses one or more files into *.zip files.

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.

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.

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

Decompressing Files

unzip

unzip foo.zip          # Unzip foo.zip into current directory

gunzip

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

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

Packages

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

tar zxvf sourcecode.tar.gz
cd sourcecode
./configure
make
make install

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Disk Usage

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

Memory Usage

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

Shutdown and Reboot

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

Identifying Processes

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

Process Priority

Process priorities go from -20 (highest) to 19 (lowest).

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

Killing Processes

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

Date & Time

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

Scheduled Tasks

   *      *         *         *           *
Minute, Hour, Day of month, Month, Day of the week

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

User Management

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

HTTP Requests

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

Network Troubleshooting

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

DNS

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

Hardware

lsusb                  # List USB devices
lspci                  # List PCI hardware
lshw                   # List all hardware

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

System Information

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

Terminal Multiplexers

Start multiple terminal sessions. Active sessions persist reboots. tmux is more modern than screen.

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

Secure Shell Protocol (SSH)

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:

$ cat ~/.ssh/config
Host name
  User foo
  Hostname 127.0.0.1
  Port 8765
$ ssh name

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Secure Copy

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

Bash Profile

• bash - .bashrc
• zsh - .zshrc

# 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

Bash Script

Variables

#!/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

#!/bin/bash
set            # List all environment variables
echo $PATH     # Print PATH environment variable
export FOO=Bar # Set an environment variable

Functions

#!/bin/bash
greet() {
local world="World"
echo "$1 $world"
return "$1 $world"
}
greet "Hello"
greeting=$(greet "Hello")

Exit Codes

#!/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

#!/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

#!/bin/bash
[[ $USER = 'rehan' ]] && echo 'yes' || echo 'no'

While Loops

#!/bin/bash
[
declare -i counter
counter=10
while [$counter -gt 2]; do
echo The counter is $counter
counter=counter-1
done
]

For Loops

#!/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

#!/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

Inspired by RehanSaeed/Bash-Cheat-Sheet

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Special characters

Linux Special Characters

Note 💡
This symbol "└─>" represents an alternative meaning of some characters.

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

Keyboard controls

Linux Keyboard Shortcuts

Some of these shortcuts may vary depending on your terminal and system.

Nano (text editor)

Vim (text editor)

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

Cheat Sheet for quick references of commands and codes

cheat.sh

ℹ️CHEAT.SH SOURCESℹ️

Cheat sheets	Repository	C/U*	Stars	Creation Date
UNIX/Linux, programming	cheat.sheets			May 1, 2017
UNIX/Linux commands	tldr-pages/tldr			Dec 8, 2013
UNIX/Linux commands	chrisallenlane/cheat			Jul 28, 2013
Programming languages	adambard/learnxinyminutes-docs			Jun 23, 2013
Go	a8m/go-lang-cheat-sheet			Feb 9, 2014
Perl	pkrumnis/perl1line.txt			Nov 4, 2011
Programming languages	StackOverflow	14M	N/A

Usage (Online)

Terminal :

curl cht.sh/keyword
# or
curl cheat.sh/keyword

Browser :

https://cht.sh/keyword
or
https://cheat.sh/keyword

Offline usage install cheat script manually

Install globally(all users) :

curl -s https://cht.sh/:cht.sh | sudo tee /usr/local/bin/cht.sh && sudo chmod +x /usr/local/bin/cht.sh

Run :

cht.sh keyword

Note - More info on usage :

https://cht.sh/:help