Capitalize first letter of each word in a selection using vim

:help case says:

To turn one line into title caps, make every first letter of a word
uppercase:
    : s/\v<(.)(\w*)/\u\1\L\2/g

Explanation:

:                      # Enter ex command line mode.

space                  # The space after the colon means that there is no
                       # address range i.e. line,line or % for entire
                       # file.

s/pattern/result/g     # The overall search and replace command uses
                       # forward slashes.  The g means to apply the
                       # change to every thing on the line. If there
                       # g is missing, then change just the first match
                       # is changed.

The pattern portion has this meaning:

\v                     # Means to enter very magic mode.
<                      # Find the beginning of a word boundary.
(.)                    # The first () construct is a capture group.
                       # Inside the () a single ., dot, means match any
                       #  character.
(\w*)                  # The second () capture group contains \w*. This
                       # means find one or more word characters. \w* is
                       # shorthand for [a-zA-Z0-9_].

The result or replacement portion has this meaning:

\u                     # Means to uppercase the following character.
\1                     # Each () capture group is assigned a number
                       # from 1 to 9. \1 or back slash one says use what
                       # I captured in the first capture group.
\L                     # Means to lowercase all the following characters.
\2                     # Use the second capture group

Result:

ROPER STATE PARK
Roper State Park

An alternate to the very magic mode:

: % s/\<\(.\)\(\w*\)/\u\1\L\2/g
# Each capture group requires a backslash to enable their meta
# character meaning i.e. "\(\)" versus "()".

You can use the following substitution:

s/\<./\u&/g

• \< matches the start of a word
• . matches the first character of a word
• \u tells Vim to uppercase the following character in the substitution string (&)
• & means substitute whatever was matched on the left-hand side
• g means substitute all matches, not only the first

The Vim Tips Wiki has a TwiddleCase mapping that toggles the visual selection to lower case, UPPER CASE, and Title Case.

If you add the TwiddleCase function to your .vimrc, then you just visually select the desired text and press the tilde character ~ to cycle through each case.

Try This regex ..

s/ \w/ \u&/g