<aside> ⚠️ The space after the opening & before the closing paranthesis / bracket is very important. Not adding a white space will cause an error.

</aside>

• String Comparisons

  • [[ $s1 = $s2 ]] or [[ $s1 == $s2 ]] → Compare if two strings are equal.
  • [[ $s1 != $s2 ]] → Compare if two strings are not equal.
  • [[ $s1 < $s2 ]]< → Is $s1 less than $s2, in ASCII alphabetical order.
  • > → Is $s1 greater than $s2, in ASCII alphabetical order.
  • [ $s1 ] → True if $s1 is not empty.
  • [ -n $s1 ] → True if length of $s1 is greater than 0.
  • [ -z $s1 ] → True if length of $s1 is equal to 0.

• Number Comparisons

  • [ n1 -eq n2 ] → True if $n1 equal to$n2.
  • [ n1 -ne n2 ] → True if $n1 is not equal to $n2 .
  • [ n1 -ge n2 ] → True if $n1 is greater than or equal to $n2.
  • [ n1 -gt n2 ] → True if $n1 is greater than $n2.
  • [ n1 -le n2 ] → True if $n1 is less than or equal to $n2.
  • [ n1 -lt n2 ] → True if $n1 is less than $n2.

• File Test Operator:

  • [ -e $file_name] → Test if a file named file_name exists.
  • [ -f $file_name] → Test if a file named file_name exists and is a regular file or not.
  • [ -b $file_name] → Test if a file named file_name exists and is a block special file or not.
  • [ -c $file_name] → Test if a file named file_name exists and is a character special file or not.
  • [ -d $dir] → Test if a directory named dir exists.
  • [ -s $file_name] → Test if a file named file_name is empty.
  • [ -r $file_name] → Test if a file named file_name has read permission.
  • [ -w $file_name] → Test if a file named file_name has write permission.
  • [ -x $file_name] → Test if a file named file_name has execute permission.

• Logical Operator

  • There's three ways to implement the AND operation
    • [ expression1 ] && [ expression2 ]
    • [ expression1 -a expression2 ]
    • [[ expression1 && expression2 ]]
  • There's three ways to implement the OR operation
    • [ expression1 ] || [ expression2 ]
    • [ expresson1 -o expression2 ]
    • [[ expression1 || expression2 ]]

• Integer Arithmetic Operator

  <aside> 📌 The below mentioned operators only works on integer type numbers.

  </aside>

  • $(( num1 + num2 )) or $(expr $num1 + $num2 ) → Addition

  • $(( num1 - num2 )) or $(expr $num1 - $num2 )→ Subtraction

  • $(( num1 * num2 )) or $(expr $num1 \* $num2 )→ Multiplication

    <aside> ⚠️ In the second method i.e., expr, do not miss the escape character \.

    </aside>

  • $(( num1 / num2 )) or $(expr $num1 / $num2 )→ Division

  • $(( num1 % num2 )) or $(expr $num1 % $num2 )→ Modulus

• Floating Point Arithmetic Operation

  To perform floating point arithmetic operations we need to use a tool called bc. The way to use the bc command is to pass the expression as an input to the command.

  • "$num1+$num2" | bc → Floating point Addition
  • "$num1-$num2" | bc → Floating point Subtraction
  • "$num1*$num2 "| bc → Floating point Multiplication
  • "scale=x;$num1/$num2" | bc → Floating point Division By default the bc command will not give any decimal output i.e., 20.5/5 = 4. To be able to get the decimal part of the output we have to set the scale of the output i.e., scale=2;20.5/5 = 4.10.
  • "$num1%$num2" | bc → Floating point Modulus

  We use the -l option with the bc command to enable the math library.

  • "$num1^$num2" | bc -l → Exponentiation
  • "scale=x;sqrt($num1)" | bc -l → Square root

  <aside> 💡 The bc command has a lot more features. Check out its man page to know more.

  </aside>

• Increment & Decrement Operators

  • $(( n++ )) →Post Increment
  • $(( n-- )) →Post Decrement
  • $(( ++n )) →Pre Increment
  • $(( --n )) →Pre Decrement