Bash Quick Start Guide

Using Bash's C-style for loops

Bash extends the for keyword to provide functionality similar to the three-argument for loop used in C:

#!/bin/bash
for ((i = 1 ; i <= 10 ; i++)) ; do
    printf '%u\n' "$i"
done

The preceding code prints the numbers from 1 to 10, each terminated by a newline, by assigning each number to the i variable in turn and then printing it. When followed by an unquoted ((, the meaning of for changes; it does not iterate over a list of words, but instead loops using the three semicolon-separated statements in the double parentheses like so:

• The first expression is run before the loop starts: We assign the i value to zero to start it off.
• The second expression is the test used to determine whether the loop should continue ...