Only get hash value using md5sum (without filename)

On Mac OS X:

md5 -q file

A simple array assignment works... Note that the first element of a Bash array can be addressed by just the name without the [0] index, i.e., $md5 contains only the 32 characters of md5sum.

md5=($(md5sum file))
echo $md5
# 53c8fdfcbb60cf8e1a1ee90601cc8fe2

Using AWK:

md5=`md5sum ${my_iso_file} | awk '{ print $1 }'`

You can use cut to split the line on spaces and return only the first such field:

md5=$(md5sum "$my_iso_file" | cut -d ' ' -f 1)