Replace only first space to a underscore in expression

[#1]

Hi,

Replace only first space to a underscore in expression

this is urgent please reply

[Anonymous]

=left('ab cd ef gh',index('ab cd ef gh', ' ',3)-1)

& '_'

& mid('ab cd ef gh',index('ab cd ef gh', ' ',3)+1)

It should work with any - just replace this '3' with 1 or 2 and try

[#3]

thanks