re_exec(3) -- Linux man page
NAMEre_comp, re_exec - BSD regex functions
DESCRIPTIONre_comp is used to compile the null-terminated regular expression pointed to by regex. The compiled pattern occupies a static area, the pattern buffer, which is overwritten by subsequent use of re_comp. If regex is NULL, no operation is performed and the pattern buffer's contents are not altered.
RETURN VALUEre_comp returns NULL on successful compilation of regex otherwise it returns a pointer to an appropriate error message.
CONFORMING TOBSD 4.3
SEE ALSOregex(7), GNU regex manual