BASH

• #!/bin/bash # this is shibang use this so if your shell is not default for bin bash this will still make it run

• echo hello world # this is used to print something on the screen Flags: -e —> is used to interpret blackslash escape for example \n for a new line will work if echo has an -e flag e.g echo -e “here \n a new line “ OR echo -e “the value for \$a is: $a”

• cat file.txt # this will display the contant of the file, it can also be used to write to a file OR create a file and write to it e.g —> <cat >> file.txt> to append to a file and <cat > file.txt> to overwrite a file , it will take your input and then to finish press ctrl + d

• hi this is a commment # this is used for commenting a line in bash

: ‘ this is used for multiple line comments ‘

any_value this is also used for multiple line comments any_value

• $variable # To call a variable use dollar sign $ for example a=10 echo $a Note : if you call a variable using ${var1} method then this method is usefull for modifying the variable , So in other words you can use this way to modify and call a variable for Example: echo “${name:0:3}” will output the value of name but from index 0 to index 3 OR for Example echo ${MESSAGE/learning/Reading} this will replace learning with reading in the value
• a=10 # to assign a variable Note that you cannot use space when signing a variable for example a = 10 this will not work and will generate an error

capture the output of a command and store it in a variable

• The syntax $(command) is used in Bash scripting to capture the output of a command and store it in a variable. for example a=$(ls), the ls command lists the files and directories in the current directory, and its output is captured and stored in the variable a. so echo $a will list everything that was stored in the directory when the variable was signed

read

• read name # ( Read is used to take input from the user ). this will take the input and make a variable named name for example hello from terminal read -p "Enter your name: " name # this is a command to take an input . <read> is used for taking input <-p> is used to display the message before taking input and <name> is then signing a value to the taken input
• echo $name this will print the value of name that is hello in the terminal # if you have used read without arguments then use echo $reply

Debugging mode

• in Debugging mode it will first show the line of code and then its working to enable or disable debugging mode one can use this —> set -x # debugging mode on OR set +x # debugging mode off. AND it will also show the error in the line it self example:
  echo when it is on when it is on ./bash: line 40: syntax error near unexpected token (' ./bash: line 40: echo Vs when it is off (bellow)' # it shows the error right in the output line and the syntax used

tr command

• tr # this is used to replace or delete a word in linux for example echo "hello world" | tr 'a-z' 'A-Z’ This command converts all lowercase letters (a-z) in "hello world" to uppercase letters (A-Z) using the pipe ( | ) to send the output of echo as input to tr # You can also use -d to only delete something

Conditional Statements in Bash