Shell Script 16 - 20

Interview Questions on Shell Script

16. How to know the exit status of last executed command?

Use $?

17. How to declare and initialize an array?

Syntax :- array_name[index]=value
Ex :- 
NAME[0]="Zara"
NAME[1]="Qadir"
NAME[2]="Mahnaz"
NAME[3]="Ayan"
NAME[4]="Daisy"

18. How to access array values?

Syntax :- array_name[index]
Ex :- 
FirstName = NAME[0];

19. How compare two variables?

-eq :- Checks if the value of two operands are equal or not, if yes then condition becomes true. 
Ex:-[ $a -eq $b ] is not true.
-ne :- Checks if the value of two operands are equal or not, if values are not equal then condition becomes true. 
Ex :- [ $a -ne $b ] is true. 

-gt :- Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. 
Ex :- [ $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 condition becomes true. 
Ex :- [ $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 condition becomes true. 
Ex :- [ $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 condition becomes true.
Ex :- [ $a -le $b ] is true.

20.  What are all the Boolean operators?
! This is logical negation. This inverts a true condition into false and vice versa. 
Ex :- [ ! false ] is true.
-o This is logical OR. If one of the operands is true then condition would be true. 
Ex :- [ $a -lt 20 -o $b -gt 100 ] is true.

-a This is logical AND. If both the operands are true then condition would be true otherwise it would be false. 
Ex :- [ $a -lt 20 -a $b -gt 100 ] is false.