In shell scripting, conditional statements are used to perform different actions based on the outcome of a comparison or test. There are several types of conditional statements that can be used, including if
, if-else
, if-elif-else
, and case
.
- if statement: The
if
statement is used to perform an action if a certain condition is true. For example:
if [ "$x" -gt "0" ]; then
echo "x is greater than 0."
fi
- if-else statement: The
if-else
statement is used to perform one action if a condition is true and another action if the condition is false. For example:
if [ "$x" -gt "0" ]; then
echo "x is greater than 0."
else
echo "x is not greater than 0."
fi
- if-elif-else statement: The
if-elif-else
the statement is used to perform different actions based on multiple conditions. For example:
if [ "$x" -gt "0" ]; then
echo "x is greater than 0."
elif [ "$x" -eq "0" ]; then
echo "x is equal to 0."
else
echo "x is less than 0."
fi
- case statement: The
case
statement is used to perform different actions based on a single variable. For example:
case $x in
1) echo "x is 1.";;
2) echo "x is 2.";;
*) echo "x is not 1 or 2.";;
esac
It’s important to note that the test conditions used in the if, if-else, if-elif-else and case statements are enclosed in square brackets ([]
) and not paranthesis (()
) as used in other programming languages. Also, it’s good practice to use double paranthesis ([[ ]]
) instead of single paranthesis ([]
) for more advanced tests, as it provides additional functionality.
It’s also good practice to use quotes around variables in the test conditions to prevent errors caused by spaces or special characters in the variable’s value.