theshell

If statements allow us to make decisions in our Bash scripts. They allow us to decide whether or not to run a piece of code based on a condition that we set.
If statements take this form:

if [condition]; then
    command1
    command2
    command3
    ...
fi

Anything between then and fi will be executed only if the condition evaluates to true.
Here is a simple example:

i=210;

if [$i -ge 200]; then
    echo "You chose a big number."
 fi

In this first example we evaluate a variable i to 105. The if statement will print "You chose a big number" only if the number contained in our variable i is Greater or Equal to 200.
This is the case, therefore the output of this piece of code will be:

  You chose a big number.

If Else

Sometimes we want to perform a certain set of actions, if our condition evaluates to true and another set of actions if our condition evaluates to false. We can do this with the if else statement. if else statements take this form:

if [condition]; then
    command1
    command2
    command3
    ...
else
    command1
    command2
    command3
    ...
fi

Here is a simple example:

i=50;

if [$i -ge 200]; then
    echo "You chose a big number."
else
    echo "You chose a small number."
fi

In this example, which is just an extension of the previous example, we evaluate a variable i to 50. If i is greater or equal to 200, we print out "You chose a big number", otherwise, (if i is not greater or equal to 200), just like in this case, we print out "You chose a small number". Therefore, the output of this piece of code is:

  You chose a small number.

If Elif Else

Sometimes, in programming, it is necessary to have a series of conditions that lead to different paths. We can accommodate this need with the if else elif mechanism. The if else elif mechanism takes this form:

if [condition]; then
    command1
    command2
    command3
    ...
elif [condition]; then
    command1
    command2
    command3
    ...
else
    command1
    command2
    command3
    ...
fi

Here is a simple example:

i=150;

if [$i -ge 200]; then
    echo "You chose a big number."
elif [$i == 150]; then
    echo "You chose 150".
else
    echo "You chose a small number"
fi

In this example, which is just an extension of the previous example, we evaluate a variable i to 150. If i is greater or equal to 200, you print out "You chose a big number", if i is equal to 150 you print out "You chose 150" otherwise you print out "You chose a small number". Therefore, the output of this piece of code is:

  You chose 150.