all-in-one/ubuntu/shell-script.md

shell Programming

• Tutorial

#!/bin/sh

echo "File Name: $0"
echo "First Parameter : $1"
echo "Second Parameter : $2"
echo "Quoted Values: $@"
echo "Quoted Values: $*"
echo "Total Number of Parameters : $#"

• while loop

#!/bin/sh

a=0
while [ "$a" -lt 10 ]    # this is loop1
do
   b="$a"
   while [ "$b" -ge 0 ]  # this is loop2
   do
      echo -n "$b "
      b=`expr $b - 1`
   done
   echo
   a=`expr $a + 1`
done

• Assume variable a holds 10 and variable b holds 20 then

Operator	Description	Example
-eq	Checks if the value of two operands are equal or not; if yes, then the condition becomes true.	[ $a -eq $b ] is not true.
-ne	Checks if the value of two operands are equal or not; if values are not equal, then the condition becomes true.	[ $a -ne $b ] is true.
-gt	Checks if the value of left operand is greater than the value of right operand; if yes, then the condition becomes true.	[ $a -gt $b ] is not true.
-lt	Checks if the value of left operand is less than the value of right operand; if yes, then the condition becomes true.	[ $a -lt $b ] is true.
-ge	Checks if the value of left operand is greater than or equal to the value of right operand; if yes, then the condition becomes true.	[ $a -ge $b ] is not true.
-le	Checks if the value of left operand is less than or equal to the value of right operand; if yes, then the condition becomes true.	[ $a -le $b ] is true.

Operator	Description	Example
!	This is logical negation. This inverts a true condition into false and vice versa.	[ ! false ] is true.
-o	This is logical OR. If one of the operands is true, then the condition becomes true.	[ $a -lt 20 -o $b -gt 100 ] is true.
-a	This is logical AND. If both the operands are true, then the condition becomes true otherwise false.	[ $a -lt 20 -a $b -gt 100 ] is false.

• Other Operator