Advanced Bash−Scripting Guide

Chapter 10. Loops and Branches
Operations on code blocks are the key to structured, organized shell scripts. Looping and branching constructs
provide the tools for accomplishing this.
10.1. Loops
A loop is a block of code that iterates (repeats) a list of commands as long as the loop control condition is
true.
for loops
for (in)
This is the basic looping construct. It differs significantly from its C counterpart.
for arg in [list]
do
command(s)...
done
During each pass through the loop, arg takes on the value of each successive variable
in the list.
for arg in "$var1" "$var2" "$var3" ... "$varN"
# In pass 1 of the loop, $arg = $var1
# In pass 2 of the loop, $arg = $var2
# In pass 3 of the loop, $arg = $var3
# ...
# In pass N of the loop, $arg = $varN
# Arguments in [list] quoted to prevent possible word splitting.
The argument list may contain wild cards.
If do is on same line as for, there needs to be a semicolon after list.
for arg in [list] ; do
Example 10−1. Simple for loops
#!/bin/bash
# List the planets.
for planet in Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
do
echo $planet
done
echo
# Entire 'list' enclosed in quotes creates a single variable.
Chapter 10. Loops and Branches 103