In Linux, all tasks from execution of services to loading and unloading of
modules are carried out by programs and all programs need to be executed. You
use the commands to access all the basic features of kernel. Shell scripting
is a way to automate such tasks, and bash is one of the language, that has
capabilities enough to be called as scripting as well as a language that can
be used for programming on the POSIX platform, for small tasks. Bash Scripting IF with AND or OR logic
Using If Statement
You can use if condition with single or multiple conditions. Starting
and ending block of this statement is define by ‘if’ and ‘fi’. Create a file
named ‘simple_if.sh’ with the following script to know the use if statement in
bash. Here, 10 is assigned to the variable, n. if the value of $n is less than
10 then the output will be “It is a one digit number”, otherwise the output
will be “It is a two digit number”. For comparison, ‘-lt’ is used here. For
comparison, you can also use ‘-eq’ for equality, ‘-ne’ for not equality and
‘-gt’ for greater than in bash script.
#!/bin/bash
n=10
if [ $n -lt 10 ];
then
echo "It is a one
digit number"
else
echo "It is a two digit number"
fi
Run the file with bash command.
OR
Using if statement with AND logic:
Different types of logical conditions can be used in if statement with two or
more conditions. How you can define multiple conditions in if statement using
AND logic is shown in the following example. ‘&&’ is used to apply AND
logic of if statement. Create a file named ‘ifWithLogic1.sh’ to check the
following code. Here, the value of username and password variables will be
taken from the user and compared with ‘admin’ and ‘secret’. If both values
match then the output will be “valid user”, otherwise the output will
be “invalid user”.
#!/bin/bash
echo "Enter username"
read username
echo "Enter
password"
read password
if [[ ( $username == "admin"
&& $password == "secret" ) ]]; then
echo "valid user"
else
echo
"invalid user"
fi
Run the file with bash command.
OR
Using if statement with OR logic:
‘||’ is used to define OR logic in if condition. Create a file named
‘ifWithLogic.sh’ with the following code to check the use of OR logic of if
statement. Here, the value of n will be taken from the user. If the value is
equal to 15 or 45 then the output will be “You won the game”, otherwise the
output will be “You lost the game”.
#!/bin/bash
echo "Enter any number"
read n
if [[ (
$n -eq 15 || $n -eq 45 ) ]]
then
echo "You won the game"
else
echo
"You lost the game"
fi
Run the file with bash command.
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