For Statement: The First Form of For

For statement

There is another loop statement in Bash called **for**. We should use for when we know the number of iterations we need in advance.

The for statement has two forms. The first one processes words in a string sequentially. The second form applies an arithmetic expression in the loop condition.

The first form of for

Let’s start with the first form of the for statement. It looks like this in the general form:

for VARIABLE in STRING
do
  ACTION
done

We can write the same construction in a single line like this:

for VARIABLE in STRING; do ACTION; done

The ACTION of the for statement is a single command or a block of commands. It is the same thing as the one in the while statement.

Bash performs all expansions in the for condition before starting the first iteration of the loop. What does it mean? Let’s suppose we specified the command instead of the STRING. Then, Bash executes this command and replaces it with its output. Also, we can specify a pattern instead of the STRING. Then, Bash expands it before starting the loop.

Bash splits the STRING into words when there are no commands or patterns left in the for condition. It takes the separators for splitting from the IFS variable.

Then, Bash executes the first iteration of the loop. The first word of the STRING is available via the VARIABLE inside the loop body on the first iteration. Then, Bash writes the second word of the STRING to the VARIABLE and starts the second iteration. This continues until we handle all words of the STRING.

Here is an example of the for loop. Let’s suppose that we need a script that prints words of a string one by one. The script receives the string via the first parameter. for-string.sh shows what its code looks like.

Click on the “Run” button and then execute the file. If we made any changes in the file, click on the “Run” button again before executing the file.