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.

Answer 2

Using awk:

$ echo "$HEAD" | awk '$1=$1'
how to remove extra spaces

Answer 3

I would make use of tr to remove the extra spaces, and xargs to trim the back and front.

TEXT="     This          is  some                             text   "
echo $(echo $TEXT | tr -s " " | xargs)

# [...]$ This is some text

Answer 4

Try this one:

echo '    how to  remove    extra        spaces                     ' | sed 's/^ *//g' | sed 's/$ *//g' | sed 's/   */ /g'

or

HEAD="    how to  remove    extra        spaces                     "
HEAD=$(echo "$HEAD" | sed 's/^ *//g' | sed 's/$ *//g' | sed 's/   */ /g')