This command matches the regular expression exp against string, and it copies string to the variable whose name is given by varName. If there is a match, then while copying string to varName the portion of string that matched exp is replaced with subSpec. in the substitution with the portion of string that matched exp. between 1 and 9, then it is replaced in the substitution with the portion of string that matched the n-th parenthesized subexpression of exp. Additional backslashes may be used in subSpec to prevent special backslash. The use of backslashes in subSpec tends to interact badly safest to enclose subSpec in braces if it includes backslashes.
If the initial arguments to regexp start with - then they are treated as switches. The following switches are currently supported:
The command returns a count of the number of matching ranges that were found and replaced. See the manual entry for regexp for details on the interpretation of regular expressions.