/bash-cheat-sheet

THE BOURNE - AGAIN SHELL

File , Directory and Access Management

Code Snippet Description
ls List the files and directories in the current directory
man ls Gives you more specific user guide/manual with the command man by giving the program name as argument
cd dir/ Change directory to the directory named dir
pwd print working directory,In Linux the home folder of a user is usually located in /home/user/, and in MacOS it’s in /Users/user/
~ It referes to users home directory, e.g the Downloads folder in Linux would be either /home/user/Downloads or ~/Downloads
. or .. Dots are often used in relative paths. One dot . refers to the current folder, and two dots .. refers to the folder the current folder is in
mkdir dir Create a new directory named dir
touch file Create a new empty file named file
rm file Delete the file named file
rm -r dir Delete the directory named dir and all its contents
chmod u+rwx file_or_directory To give read,write, and execute permissions to the owner of a file or directory
chmod g+rwx file_or_directory To give read, write, and execute permissions to the group associated with a file or directory:
chmod a+rwx file_or_directory To give read, write, and execute permissions to all users (i.e. the owner, group, and others):
chmod a-x file_or_directory To remove execute permission for all users from a file or directory:
chmod 755 file_or_directory To set the permissions of a file or directory to a specific octal value, for example, 755 (rwxr-xr-x):
chmod -R permissions file_or_directory To set the permissions of a file or directory recursively, including all files and subdirectories within it:

File Mods(permissions)

Mod Value Shorthand
Read 4 r
Write 2 w
Execute 1 x

Classes of users

Shorthand Class Description
u Owner /user Who own the file
g Group users in the file's group
o Others All other users
a All evertything above

Common Unix commands

Code Snippet Description
cal Show Calender
clear clear screen
wc Count number of lines, characters, words etc wc /tmp/test.txt
whoami Print current user name
uname Show system Information uname -a
df get Information about disk usage capacity df -h

Unix file system

Code Snippet Description
/ Root of the file system
/bin Binary - containing executable programs(such as ls,cp)
/dev Devices - containing files represeting devices
/dev/null If you dont want to show the output you can send it to /dev/null, ls -l jfdkjfd 2>/dev/null (2 & 1 means using the same target for both output & error streams, /dev/null is a null file) the error message will go to the null file which will descarded, ls -l >/dev/null this is a correct message will go also to null file
/etc Containing system configurations & databases
/home Home directory for users
/lib Containing system libraries & device drivers
/tmp For temprary files
/usr Containing non system-critical libraries, executables

Moving and Renaming files

Code Snippet Description
cp cp (copy) It takes the path to the file to be copied and the target path as arguments
cp example.txt example2.txt copies the file example.txt as a file called example2.txt in the current folder.
cp example.txt ~/Documents/example2.txt copies the file example.txt to the Documents folder and renames it to example2.txt
cp example.txt ~/Documents/ copies the file to Documents and keeps the name as example.txt
cp -R testFolder2/ testForlder/ copies the folder2 to folder
mv exmple.txt example.txt Renames the file exmple.txt to example.txt.
mv example.txt ~ Moves the file example.txt from the current folder to the home folder.
mv exmple.txt ~/example.txt renames the file exmple.txt from the current folder to example.txt and moves it to the home folder.
mv ~/example.txt ~/Downloads/ moves the file example.txt from the home folder to the Downloads folder.
rm -r CS2 or rm -r -f CS2 would remove the directory named "CS2" and all its contents without prompting for confirmation.-r stands for recursive and will remove all directories and files within the specified directory
-f stands for force and will not prompt for confirmation before removing files or directories, It's important to use this command with caution

Wild Cards

Wild cards allow one to perform operations on several files at the same time.

Code Snippet Description
* It corresponds to any amount of any given symbol.
mv *.txt example/ moves all the files in the current directory ending with .txt to a folder caller example
mv test* tests/ would move all the files starting with test to a folder called tests.

System Information and Management

Code Snippet Description
ps List the currently running processes
top Display real-time system information, including CPU usage and memory usage
htop Interactive process viewer, similar to top
lscpu Check CPU Information
lsmem Check Memory(RAM) Information
kill pid Terminate the process with the specified process ID
sudo command Run the specified command with administrative privileges
ps -ax | less View and navigate long file
ps -ax | grep /usr/local/bin/node | awk {print $1} Print process ID (pid) of node programs

Shell vs Scripts

Code Snippet Description
shell Is an interface bn user and kernel
bash When a user login the bash starts, bash => name of your shell
echo $0 To check what shell is active when a user login
echo $SHELL to see the default shell
cat /etc/shells To see a list of default shells

Commonly Used Bash Commands for Network Management

Code Snippet Description
ping [address] Sends an ICMP echo request to a specific network address to test network connectivity.
traceroute [address] Displays the path that packets take to reach a network address, along with the time taken by each hop.
netstat Displays active network connections, routing tables, and related network statistics.
netstat -tupan Display all the active TCP and UDP connections on your system along with the associated process or program name, IP address, and port number.
ifconfig Displays the configuration of network interfaces, including IP addresses and network masks.
route Displays and modifies the routing table of the network stack.
arp Displays and modifies the ARP cache, which maps network addresses to physical addresses.
ssh [user@]host Connects to a remote host over the network using the SSH protocol.
scp [options] [source] [destination] Copies files securely between hosts over the network using the SSH protocol.
wget [URL] Downloads files from the network using HTTP, HTTPS, or FTP protocols.
curl [options] [URL] Downloads or uploads data to or from the network using various protocols, including HTTP, HTTPS, FTP, and SCP.

Text Processing and Manipulation

Code Snippet Description
cat file Display the contents of the file named file
grep pattern file Search for lines in the file named file that match the specified pattern
sed 's/old/new/g' file Replace all occurrences of old with new in the file named file
awk '{print $1}' file Print the first field of each line in the file named file
cut -d',' -f1 file Extract the first column of a CSV file named file
> writing outputs to files , also overwrites the contents of the file with the given text
>> appends the new content to a new line, not affecting the old contents. like >
< Input Stream, or reading from a file cat < java.txt reads text from the file
wc -l countLinus.txt The wc command is used to find the number of lines, characters, words, and bytes of a file

Search commands from Terminal

Code Snippet Description
grep pattern file_name Search for the specified pattern in the specified file
grep -r pattern directory_name Search for the specified pattern in all files in the specified directory and its subdirectories
grep -i "unix" linux.txt Search for "unix" text in the linux file, ignoring case
grep U* linux.txt Search for text in the linux file, that begins with uppre case U
| usually called the pipe. With the pipe you can do more complicated operations which require several programs with just one line. `~/example$ ls
grep -i u* linux.txt > result.txt Write all the outputs from left side into right side file, creating the file if it doesn’t already exist.
grep -w pattern file_name Search for the specified word as a whole word in the specified file
ps -ax | grep /usr/local/bin/node | awk '{print $1}' > ./pids.txt What this command does?
find directory_path -name file_name Search for files with the specified name in the specified directory and its subdirectories
find directory_path -type f -mtime +n Search for files modified more than n days ago in the specified directory and its subdirectories
find directory_path -type f -size +n[cwbkMG] Search for files larger than n units (cwbkMG) in the specified directory and its subdirectories
history Display the list of commands executed in the current terminal session
history n Display the last n commands executed in the current terminal session
history -c Clear the command history for the current terminal session
history -a Append the commands executed in the current terminal session to the history file
history -r Read the commands from the history file and append them to the current session history
history grep pattern Search for commands that contain the specified pattern in the current session history
ls .bash_history get history file
cat .bash_history display list of history command
ctr + r Search commands In the Terminal

Bash in Vim Editor

Code Snippet Description
#!/bin/bash Its called shebang line for a Bash script, which specifies the interpreter that should be used to run the script. In this case, the shebang line specifies that the script should be run using the Bash interpreter. Its Always should be in first line
# This is a bash comment Single line comment
: ' Multiple line ' Multiple line comment
: set nu To insert code line number in Vim editor
:set nonu To remove code line number in Vim editor
set nu If you want to see code line number in Vim editor Every time, NB. no colun(:) in this case
chmod +x first_script.sh Run Bash on Terminal, always add execution Permission

Standard Streams

standard Image

Environment Variables(env)

Code Snippet Description
env It will print a list of all environment variables and their values, It also displays the current environment variables for the current shell session
env less Command is a text pager that allows you to view long text files or command output one page at a time.
env | grep user Search for user
printenv or printenv HOME Prints only the specified environment variable
printenv SHELL LC_TIME PWD prints the values accordingly
set | grep HIST Search valriables

Install packages / softwares in Linux environment

Code Snippet Description
apt
env less Command is a text pager that allows you to view long text files or command output one page at a time.
env | grep user Search for user
printenv or printenv HOME Prints only the specified environment variable
printenv SHELL LC_TIME PWD prints the values accordingly
set | grep HIST Search valriables

Others

Code Snippet Description
alias Is a shortcut to a command e.g alias server=ssh -p 2299 admin@189.24.5.6
alias alias_name=´command_to_run To create an alias, nano ~/.bashrc , eg. alias now=date +%F\ %T, then source ~/.bashrc, will update the bash