How to remove extra spaces in bash?

Question

How to remove extra spaces in variable HEAD?

HEAD=\"    how to  remove    extra        spaces                     \"

Result:

Answer 1

Here's how I would do it with sed:

string='    how to  remove    extra        spaces                     '
echo "$string" | sed -e 's/  */ /g' -e 's/^ *\(.*\) *$/\1/'

=> how to remove extra spaces   # (no spaces at beginning or end)

The first sed expression replaces any groups of more than 1 space with a single space, and the second expression removes any trailing or leading spaces.