====== BASH - if...then...else ======

If takes the form:

<code bash>
if CONDITION 
then
STATEMENTS
fi
</code>

<WRAP info>
**NOTE:**  The statements are only executed if the CONDITION is true.

The **fi** keyword is used for marking the end of the **if** statement.

</WRAP>


----


===== Example =====

<code bash>
#!/bin/bash

echo -n "Enter a number: "
read num

if [[ $num -gt 10 ]]
then
echo "Number is greater than 10."
fi
</code>

<WRAP info>
**NOTE:**  The above program will only show the output if the number entered is greater than ten.

The space around the **<nowiki>[[ ]]</nowiki>** are required!

  * **-gt**:  stands for greater than;

Similarly:

  * **-lt**:  for less than.
  * **-le**:  for less than or equal.
  * **-ge**:  for greater than or equal.



</WRAP>

----

===== More Control Using If Else =====

Combining the else construct with if allows much better control over the script’s logic.

<code bash>
#!/bin/bash

read n
if [ $n -lt 10 ];
then
echo "It is a one digit number"
else
echo "It is a two digit number"
fi
</code>

<WRAP info>
**NOTE:**  The **else** part needs to be placed after the action part of **if** and before **fi**.
</WRAP>


----

===== Using Elif =====

The **elif** statement stands for 'else if' and offers a convenient means for implementing chain logic.

<code bash>
#!/bin/bash

echo -n "Enter a number: "
read num

if [[ $num -gt 10 ]]
then
echo "Number is greater than 10."
elif [[ $num -eq 10 ]]
then
echo "Number is equal to 10."
else
echo "Number is less than 10."
fi
</code>

----

===== AND =====

Use **&&**.

<code bash>
#!/bin/bash

echo -n "Enter Number:"
read num

if [[ ( $num -lt 10 ) && ( $num%2 -eq 0 ) ]]; then
echo "Even Number"
else
echo "Odd Number"
fi
</code>

----

===== OR =====

Use **||**.


<code bash>
#!/bin/bash

echo -n "Enter any number:"
read n

if [[ ( $n -eq 15 || $n -eq 45 ) ]]
then
echo "You won"
else
echo "You lost!"
fi
</code>

----

===== References =====

See [[BASH:Switch|Switch]]