Bash Shell Script Iterate Through Array Values

Posted August 30, 2004 by Quinn McHenry in Bourne shell scripting

Having an array of variables is of no use unless you can use those values somehow. This tech-recipe shows a few methods for looping through the values of an array in the bash shell.


Take, for example, the array definition below:

names=( Jennifer Tonya Anna Sadie )

The following expression evaluates into all values of the array:

${names[@]}

It also can be used anywhere a variable or string can be used.

A simple for loop can iterate through this array one value at a time:

for name in ${names[@]}
do
echo $name
# other stuff on $name
done

This script will loop through the array values and print them out, one per line. Additional statements can be placed within the loop body to take further action, such as modifying each file in an array of filenames.

Sometimes it is useful to loop through an array and know the numeric index of the array you are using (for example, so that you can reference another array with the same index). The same loop in the example above can be achieved this way, too:

for (( i = 0 ; i < ${#names[@]} ; i++ )) do echo ${names[$i]} # yadda yadda done

In this example, the value ${#names[@]} evaluates into the number of elements in the array (4 in this case). The individual elements of the array are accessed, one at a time, using the index integer $i as ${names[$i]}

 

About Quinn McHenry

Quinn was one of the original co-founders of Tech-Recipes. He is currently crafting iOS applications as a senior developer at Small Planet Digital in Brooklyn, New York.
View more articles by Quinn McHenry

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