until command do Statement(s) to be executed until command is true done
until command do Statement(s) to be executed until command is true done
At particular condion if we want to come out of loop then we can use break.
if we want to skip particular condition then we can use break.
Syntax :- if [ expression 1 ] then Statement(s) to be executed if expression 1 is true Statement(s) to be executed if no expression is true fi
Syntax :- if [ expression 1 ] then Statement(s) to be executed if expression 1 is true elif [ expression 2 ] then Statement(s) to be executed if expression 2 is true else Statement(s) to be executed if no expression is true fi
Syntax :-
case word in
pattern1)
Statement(s) to be executed if pattern1 matches
;;
pattern2)
Statement(s) to be executed if pattern2 matches
;;
pattern3)
Statement(s) to be executed if pattern3 matches
;;
esac
while command do Statement(s) to be executed if command is true done
for var in word1 word2 ... wordN do Statement(s) to be executed for every word. done
Use $?
Syntax :- array_name[index]=value Ex :- NAME[0]="Zara" NAME[1]="Qadir" NAME[2]="Mahnaz" NAME[3]="Ayan" NAME[4]="Daisy"
Syntax :- array_name[index] Ex :- FirstName = NAME[0];
-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.
use unset $ unset PI
Prints procees id of current shell.
The filename of the current script.
The number of arguments supplied to a script.
Prints all arguments.
sh filename.sh
syntax: bash your-script-name sh your-script-name ./your-script-name Examples : $ bash bar $ sh bar $ ./bar 8. What are all the types of variables? 1) System variables - Created and maintained by Linux itself. This type of variable defined in CAPITAL LETTERS. 2) User defined variables (UDV) - Created and maintained by user. This type of variable defined in lower letters.
Syntax: variable name=value NOTE: Here 'value' is assigned to given 'variable name' and Value must be on right side = sign.
Use readonly $ readonly PI=3.14
A shell script is a program file that runs unix commands based on the conditions for a UNIX-based operating system.
Two main types of shells: The Bourne shell :- If you are using a Bourne-type shell, the default prompt is the $ character. The C shell :- If you are using a C-type shell, the default prompt is the % character.
#!/bin/bash clear echo “Hello World"
Start with # and then write comment lines. Ex :- # Commnets goes here
Generally we use .sh extension for shell sctipt.