subst ';' STRING ';' REGEX (';' STRING (';' NUMBER )? )?
Macro
Substitute all the regex matches in the target for the given value; if a count is specified, limit the number of replacements to that count.
subst ; <target> ; <regex> [ ; <replacement> [ ; <count> ] ]
Substitute the substrings that match the <regex> in the the <target> with the replacement. The default replacement is the empty string. The default count is all.
Examples
${subst;foo.bar;.bar} => foo