perl -nle "my (@c) = /\:(\w+)\:/g; print join '.', @c"
 input> out:caputure1:out:capture2:out
output> caputure1.capture2

##</code><code>##

perl -nle "my (@c) = s/\:(\w+)\:/X/g; print join '.', @c"
 input> out:caputure1:out:capture2:out
output> 2