Quick review for commands

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

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

Command History

history                                # View all previous commands
history | grep saman                   # View the commands using a specific word
history | grep -E|--extended-regexp -i|--ignore-case 'saman1|saman2|saman3' # 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 saman.sh                         # <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<┐
chmod +x !$                            # !$ is the last argument of the last command i.e. saman.sh <<<<┘

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 saman.txt            # List size, created and modified timestamps for a file
stat saman                # 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 saman                  # Go to saman sub-directory
cd                        # Go to home directory
cd ~                      # Go to home directory
cd -                      # Go to the previously chosen directory
pushd saman               # Go to saman sub-directory and add previous directory to stack
popd                      # Go back to directory in stack saved by `pushd`

Creating Directories

mkdir saman                        # Create a directory
mkdir saman bar                    # Create multiple directories
mkdir -p|--parents saman/bar       # Create nested directory
mkdir -p|--parents {saman,bar}/baz # Create multiple nested directories

mktemp -d|--directory              # Create a temporary directory

Moving Directories

cp -R|--recursive saman bar                              # Copy directory
mv saman bar                                             # Move directory

rsync -z|--compress -v|--verbose /saman /bar             # Copy directory, overwrites destination
rsync --ignore-existing -a|--archive -z|--compress -v|--verbose /saman /bar # Copy directory, without overwriting destination
rsync -avz /saman username@hostname:/bar                 # Copy local directory to remote directory
rsync -avz username@hostname:/saman /bar                 # Copy remote directory to local directory

Deleting Directories

rmdir saman                        # Delete non-empty directory
rm -r|--recursive saman            # Delete directory including contents
rm -r|--recursive -f|--force saman # Delete directory including contents, ignore nonexistent files and never prompt

Creating Files

touch saman.txt          # Create file or update existing files modified timestamp
touch saman.txt bar.txt  # Create multiple files
touch {saman,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

Standard Output, Standard Error and Standard Input

echo "saman" > bar.txt     # Overwrite file with content
echo "saman" >> 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 saman                 # Read from standard input and write to the variable saman

Moving Files

cp saman.txt bar.txt                                 # Copy file
mv saman.txt bar.txt                                 # Move file

rsync -z|--compress -v|--verbose /saman.txt /bar     # Copy file quickly if not changed
rsync -z|--compress -v|--verbose /saman.txt /bar.txt # Copy and rename file quickly if not changed

Deleting Files

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

Reading Files

cat saman.txt              # Print all contents
less saman.txt             # Print some contents at a time (g - go to top of file, SHIFT+g, go to bottom of file, /saman to search for 'saman')
head saman.txt             # Print top 10 lines of file
tail saman.txt             # Print bottom 10 lines of file
tail -f|--follow saman.txt # Print bottom 10 lines of file updating with new data
open saman.txt             # Open file in the default editor
wc saman.txt               # List number of lines words and characters in the file

Sorting Files

sort saman.txt                                  # Sort file (ascending order) 
sort -r|--reverse saman.txt                     # Sort file (descending order) 
sort -n|--numeric-sort saman.txt                # Sort numbers instead of strings 
sort -t|--field-separator: -k 3n /saman/saman.txt # Sort by the third column of a file

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

ls -l /saman.sh            # List file permissions
chmod +100 saman.sh        # Add 1 to the user permission
chmod -100 saman.sh        # Subtract 1 from the user permission
chmod u+x saman.sh         # Give the user execute permission
chmod g+x saman.sh         # Give the group execute permission
chmod u-x,g-x saman.sh     # Take away the user and group execute permission
chmod u+x,g+x,o+x saman.sh # Give everybody execute permission
chmod a+x saman.sh         # Give everybody execute permission
chmod +x saman.sh          # Give everybody execute permission

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 saman.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 saman.txt                   # Find a file
find /path -iname saman.txt                  # Find a file with case insensitive search
find /path -name "*.txt"                   # Find all text files
find /path -name saman.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 saman.txt           # Find a file
find /path -type d -name saman               # Find a directory
find /path -type l -name saman.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

Find in Files

grep 'saman' /bar.txt                         # Search for 'saman' in file 'bar.txt'
grep 'saman' /bar -r|--recursive              # Search for 'saman' in directory 'bar'
grep 'saman' /bar -R|--dereference-recursive  # Search for 'saman' in directory 'bar' and follow symbolic links
grep 'saman' /bar -l|--files-with-matches     # Show only files that match
grep 'saman' /bar -L|--files-without-match    # Show only files that don't match
grep 'saman' /bar -i|--ignore-case            # Case insensitive search
grep 'saman' /bar -x|--line-regexp            # Match the entire line
grep 'saman' /bar -C|--context 1              # Add N line of context above and below each search result
grep 'saman' /bar -v|--invert-match           # Show only lines that don't match
grep 'saman' /bar -c|--count                  # Count the number lines that match
grep 'saman' /bar -n|--line-number            # Add line numbers
grep 'saman' /bar --colour                    # Add colour to output
grep 'saman\|bar' /baz -R                     # Search for 'saman' or 'bar' in directory 'baz'
grep --extended-regexp|-E 'saman|bar' /baz -R # Use regular expressions
grep -E 'saman|bar' /baz -R                   # Use regular expressions

Replace in Files

sed 's/fox/bear/g' saman.txt                          # Replace fox with bear in saman.txt and output to console
sed 's/fox/bear/gi' saman.txt                         # Replace fox (case insensitive) with bear in saman.txt and output to console
sed 's/red fox/blue bear/g' saman.txt                 # Replace red with blue and fox with bear in saman.txt and output to console
sed 's/fox/bear/g' saman.txt > bar.txt                # Replace fox with bear in saman.txt and save in bar.txt
sed -i|--in-place 's/fox/bear/g' saman.txt            # Replace fox with bear and overwrite saman.txt
sed -i|--in-place '/red fox/i\blue bear' saman.txt    # Insert blue bear before red fox and overwrite saman.txt
sed -i|--in-place '/red fox/a\blue bear' saman.txt    # Insert blue bear after red fox and overwrite saman.txt
sed -i|--in-place '10s/find/replace/' saman.txt       # Replace the 10th line of the file 
sed -i|--in-place '10,20s/find/replace/' saman.txt    # Replace in the file 10-20 lines 

File Editor

nano                              # Open a new file in nano
nano saman.txt                      # Open a specific file
nano -m|--mouse saman.txt           # Enable the use of the mouse
nano -l|--linenumbers saman.txt     # Show line numbers in front of the text
nano +line,10 saman.txt             # Open file positioning the cursor at the specified line and column
nano -B|--backup saman.txt          # Create a backup file (`saman~`) when saving edits

Symbolic Links

ln -s|--symbolic saman bar            # Create a link 'bar' to the 'saman' folder
ln -s|--symbolic -f|--force saman bar # Overwrite an existing symbolic link 'bar'
ls -l                               # Show where symbolic links are pointing

Compressing Files

zip

Compresses one or more files into *.zip files.

zip saman.zip /bar.txt                # Compress bar.txt into saman.zip
zip saman.zip /bar.txt /baz.txt       # Compress bar.txt and baz.txt into saman.zip
zip saman.zip /{bar,baz}.txt          # Compress bar.txt and baz.txt into saman.zip
zip -r|--recurse-paths saman.zip /bar # Compress directory bar into saman.zip

gzip

Compresses a single file into *.gz files.

gzip /bar.txt saman.gz           # Compress bar.txt into saman.gz and then delete bar.txt
gzip -k|--keep /bar.txt saman.gz # Compress bar.txt into saman.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=saman.tgz /bar.txt /baz.txt # Compress bar.txt and baz.txt into saman.tgz
tar -c|--create -z|--gzip -f|--file=saman.tgz /{bar,baz}.txt    # Compress bar.txt and baz.txt into saman.tgz
tar -c|--create -z|--gzip -f|--file=saman.tgz /bar              # Compress directory bar into saman.tgz

Decompressing Files

unzip

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

gunzip

gunzip saman.gz           # Unzip saman.gz into current directory and delete saman.gz
gunzip -k|--keep saman.gz # Unzip saman.gz into current directory

tar -x

tar -x|--extract -z|--gzip -f|--file=saman.tar.gz # Un-compress saman.tar.gz into current directory
tar -x|--extract -f|--file=saman.tar              # Un-combine saman.tar into current directory

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
rpm -i|--install package_name.rpm   # Install rpm file 

Install package source code

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

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 /saman/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

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

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

Identifying Processes

top                    # List all processes interactively
htop                   # List all processes interactively
ps ax                  # List all processes
pidof saman              # Return the PID of all saman 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

Process Priority

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

nice -n -20 saman        # Change process priority by name
renice 20 PID          # Change process priority by PID
ps -o ni PID           # Return the process priority of PID

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 saman              # Shut down process by name gracefully. Sends TERM signal.
pkill -9 saman           # force shut down process by name. Sends SIGKILL signal.
killall saman            # Kill all process with the specified name gracefully.

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

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

* * * * * saman              # Run saman every minute
*/15 * * * * saman           # Run saman every 15 minutes
0 * * * * saman              # Run saman every hour
15 6 * * * saman             # Run saman daily at 6:15 AM
44 4 * * 5 saman             # Run saman every Friday at 4:44 AM
0 0 1 * * saman              # Run saman at midnight on the first of the month
0 0 1 1 * saman              # Run saman 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

User Management

sudo su                                            # Switch to root user
sudo saman                                           # Execute commands(has permission denied) as the root user
sudo nano /saman/saman.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

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 saman.txt https://example.com      # Output to a text file
curl -H|--header "User-Agent: saman" https://example.com # Add a HTTP header
curl -X|--request POST -H "Content-Type: application/json" -d|--data '{"saman":"bar"}' https://example.com # POST JSON
curl -X POST -H --data-urlencode saman="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 saman.txt https://example.com/file.txt # Output to a file with the specified name

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

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

Hardware

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

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

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 saman    # 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)

Secure Shell Protocol (SSH)

ssh hostname                 # Connect to hostname using your current user name over the default SSH port 22
ssh -i saman.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 saman
  Hostname 127.0.0.1
  Port 8765
$ ssh name

Secure Copy

scp saman.txt ubuntu@hostname:/home/ubuntu                  # Copy saman.txt into the specified remote directory
scp ubuntu@hostname:/home/ubuntu/saman.txt /C:\Users\Admin    # Copy saman.txt from the specified remote directory

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'

Conditional Statements

Boolean Operators

• $saman - Is true

• !$saman - 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 saman.txt - Check file exists

• -z saman - 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 [[$saman = 'bar']]; then
  echo 'one'
elif [[$saman = 'bar']] || [[$saman = 'baz']]; then
  echo 'two'
elif [[$saman = 'ban']] && [[$USER = 'bat']]; then
  echo 'three'
else
  echo 'four'
fi
]]

Inline If Statements

#!/bin/bash

[[ $USER = 'saman' ]] && 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