for-loop

Most of you probably know how a for-loop is supposed to work. We want to be able to repeat a certain code n number of times, or loop through the contents of a data structure.

for…in

#!/usr/bin/env bash
#
# An example script on for...in

# for...in range
for value in 1 2 3 4 5
do
    echo "$value"
done

# for...in range, ({START..END})
for value in {1..5}
do
    echo "$value"
done

# for...in range with steps, ({START..END..INCREMENT})
for value in {1..10..2}
do
    echo "$value"
done

An alternative is to use arithmetic expansion, (( )). It gives the opportunity to write a more C-like construction. Note that it also works for the conditions in the if statement.

#!/usr/bin/env bash
#
# An example script on traditional for-loop

for (( i=0; i<10; i++ ))
do
    if (( "$i" % 2 == 0 ))
    then
        echo "$i is even"
    else
        echo "$i is odd"
    fi    
done

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