How to count number of words from String using shell

Try the following one-liner:

echo $(c() { echo $#; }; c $input)

It basically defines c() function and passes $input as the argument, then $# returns number of elements in the argument separated by whitespace. To change the delimiter, you may change IFS (a special variable).

You don't need an external command like wc because you can do it in pure bash which is more efficient.

Convert the string into an array and then count the elements in the array:

$ input="Count from this String   "
$ words=( $input )
$ echo ${#words[@]}
4

Alternatively, use set to set positional parameters and then count them:

$ input="Count from this String   "
$ set -- $input
$ echo $#
4

To do it in pure bash avoiding side-effects, do it in a sub-shell:

$ input="Count from this string "
$ echo $(IFS=' '; set -f -- $input; echo $#)
4

It works with other separators as well:

$ input="dog,cat,snake,billy goat,horse"
$ echo $(IFS=,; set -f -- $input; echo $#)
5
$ echo $(IFS=' '; set -f -- $input; echo $#)
2

Note the use of "set -f" which disables bash filename expansion in the subshell, so if the caller wants expansion it should be done beforehand (Hat Tip @mkelement0).

echo "$input" | wc -w

Use wc -w to count the number of words.

Or as per dogbane's suggestion, the echo can be got rid of as well:

wc -w <<< "$input"

If <<< is not supported by your shell you can try this variant:

wc -w << END_OF_INPUT
$input
END_OF_INPUT