Shell Scripting-3

Special variables

$$ – This represents the process ID number (PID) of the current shell.
$0 – This variable represents the file name of the current script.$0 --it shows shell script name - dbbackup.sh

$# – This variable represents the number of arguments that are provided to a script.

$* -- all the args - it will give all the args as one string

$@ -- all the args - it will give each arg as a one one-string

$? -- previous command execution status

$! – This variable represents the process number of the last background command

command line arguments

during shell script execution, values passing through the command prompt are called command line arguments

for ex: while running a shell script we can specify the command line arguments as a sh script file.sh arg1 arg2 arg3"

important points while using CLA

we can specify n number of arguments, there is no limitation
each argument is separated by space

#!/bin/sh

echo “Script name: $0”

echo “My First favorite fruit: $1”

echo “My Second favorite fruit: $2”

echo “Total number of fruits: $#”
output

$./fruit.shPineapple Mango

Script name: ./fruit.sh

My first favorite fruit: Pineapple

My second favorite fruit: Mango

Total Number of fruit:2

-eq = equal =

-ne =not equal to

-lt = less then

-le = less than or equal to

-gt =greater then

-ge = greater than or equal to

output

We can use the symbols of the equation

-eq...... ==

-le....... < =

-lt........ <

-ge...... > =

-gt...... >

-ne...... !=

Array

It is a sequential memory location

if you store the variable in the array, we get what we want to display names

An array variable is capable of holding multiple values at the same time

array_name = (value1, value2 … valuen)

After creating the array variable, we can access the same in the following way –

${array_name[index]}

array_name represents the name of the array and index represents the index of the value

#!/bin/sh

FRUIT[0] = “Pineapple”

FRUIT[1] = “Mango”

FRUIT[2] = “Apple”

FRUIT[3] = “Grapes”

FRUIT[4] = “Banana”

echo “All the fruits present in the array are : ${FRUIT[*]}”

execution : $./fruit.sh

output: All the fruits present in the array are: Pineapple Mango Apple Grapes Banana

strings

zero or more characters enclosed in a single or double quotes

example : name = "kusuma" ,' Suma'

name is a variable
kusuma , Suma is a string

echo $string_var or echo $(string_var) ----- it is going to display the value of the string value

echo ${#string_var}---- it will give the length of the variable

echo ${string_var} Kusuma l, working in an organization, Infosys ------it is going to show value only after the 20 words i.e it counts even the space and all explanatory marks

echo ${string_var:20:14} Kusuma ----- the first number is for how many characters we have to leave and the second number is how many to display

echo ${string_var: -8}organization

vi string.sh