Basic Regexp functionality in 30 lines of C

gistfile1.c

/* match: search for regexp anywhere in text */
int match(char *regexp, char *text)
{
    if (regexp[0] == '^')
        return matchhere(regexp+1, text);
    do {    /* must look even if string is empty */
        if (matchhere(regexp, text))
            return 1;
    } while (*text++ != '\0');
    return 0;
}

/* matchhere: search for regexp at beginning of text */
int matchhere(char *regexp, char *text)
{
   if (regexp[0] == '\0')
       return 1;
   if (regexp[1] == '*')
       return matchstar(regexp[0], regexp+2, text);
	   if (regexp[0] == '$' && regexp[1] == '\0')
       return *text == '\0';
   if (*text!='\0' && (regexp[0]=='.' || regexp[0]==*text))
       return matchhere(regexp+1, text+1);
   return 0;
}

/* matchstar: search for c*regexp at beginning of text */
int matchstar(int c, char *regexp, char *text)
{
   do {   /* a * matches zero or more instances */
       if (matchhere(regexp, text))
           return 1;
   } while (*text != '\0' && (*text++ == c || c == '.'));
   return 0;
}