2 files changed, 28 insertions, 4 deletions
diff --git a/src/libutil/regex.cc b/src/libutil/regex.cc
index 36c8458cee08..84274b3e1da9 100644
--- a/src/libutil/regex.cc
+++ b/src/libutil/regex.cc
@@ -1,13 +1,16 @@
 #include "regex.hh"
 #include "types.hh"
 
+#include <algorithm>
+
 namespace nix {
 
-Regex::Regex(const string & pattern)
+Regex::Regex(const string & pattern, bool subs)
 {
     /* Patterns must match the entire string. */
-    int err = regcomp(&preg, ("^(" + pattern + ")$").c_str(), REG_NOSUB | REG_EXTENDED);
-    if (err) throw Error(format("compiling pattern ‘%1%’: %2%") % pattern % showError(err));
+    int err = regcomp(&preg, ("^(" + pattern + ")$").c_str(), (subs ? 0 : REG_NOSUB) | REG_EXTENDED);
+    if (err) throw RegexError(format("compiling pattern ‘%1%’: %2%") % pattern % showError(err));
+    nrParens = subs ? std::count(pattern.begin(), pattern.end(), '(') : 0;
 }
 
 Regex::~Regex()
@@ -23,6 +26,20 @@ bool Regex::matches(const string & s)
     throw Error(format("matching string ‘%1%’: %2%") % s % showError(err));
 }
 
+bool Regex::matches(const string & s, Subs & subs)
+{
+    regmatch_t pmatch[nrParens + 2];
+    int err = regexec(&preg, s.c_str(), nrParens + 2, pmatch, 0);
+    if (err == 0) {
+        for (unsigned int n = 2; n < nrParens + 2; ++n)
+            if (pmatch[n].rm_eo != -1)
+                subs[n - 2] = string(s, pmatch[n].rm_so, pmatch[n].rm_eo - pmatch[n].rm_so);
+        return true;
+    }
+    else if (err == REG_NOMATCH) return false;
+    throw Error(format("matching string ‘%1%’: %2%") % s % showError(err));
+}
+
 string Regex::showError(int err)
 {
     char buf[256];
diff --git a/src/libutil/regex.hh b/src/libutil/regex.hh
index aa012b721cb7..53e31f4edc4a 100644
--- a/src/libutil/regex.hh
+++ b/src/libutil/regex.hh
@@ -5,16 +5,23 @@
 #include <sys/types.h>
 #include <regex.h>
 
+#include <map>
+
 namespace nix {
 
+MakeError(RegexError, Error)
+
 class Regex
 {
 public:
-    Regex(const string & pattern);
+    Regex(const string & pattern, bool subs = false);
     ~Regex();
     bool matches(const string & s);
+    typedef std::map<unsigned int, string> Subs;
+    bool matches(const string & s, Subs & subs);
 
 private:
+    unsigned nrParens;
     regex_t preg;
     string showError(int err);
 };