-alertnotify=<cmd>

Runs a shell command when an AppliesToMe() alert is received.
%s in the <cmd> string is replaced with the alert.strStatusBar
message.

src/alert.cpp

@@ -2,6 +2,9 @@
 // Alert system
 //
 
+#include <algorithm>
+#include <boost/algorithm/string/classification.hpp>
+#include <boost/algorithm/string/replace.hpp>
 #include <boost/foreach.hpp>
 #include <map>
 
@@ -165,7 +168,7 @@ CAlert CAlert::getAlertByHash(const uint256 &hash)
     return retval;
 }
 
-bool CAlert::ProcessAlert()
+bool CAlert::ProcessAlert(bool fThread)
 {
     if (!CheckSignature())
         return false;
@@ -229,9 +232,35 @@ bool CAlert::ProcessAlert()
 
         // Add to mapAlerts
         mapAlerts.insert(make_pair(GetHash(), *this));
-        // Notify UI if it applies to me
+        // Notify UI and -alertnotify if it applies to me
         if(AppliesToMe())
+        {
             uiInterface.NotifyAlertChanged(GetHash(), CT_NEW);
+            std::string strCmd = GetArg("-alertnotify", "");
+            if (!strCmd.empty())
+            {
+                // Alert text should be plain ascii coming from a trusted source, but to
+                // be safe we first strip anything not in safeChars, then add single quotes around
+                // the whole string before passing it to the shell:
+                std::string singleQuote("'");
+                // safeChars chosen to allow simple messages/URLs/email addresses, but avoid anything
+                // even possibly remotely dangerous like & or >
+                std::string safeChars("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890 .,;_/:?@");
+                std::string safeStatus;
+                for (std::string::size_type i = 0; i < strStatusBar.size(); i++)
+                {
+                    if (safeChars.find(strStatusBar[i]) != std::string::npos)
+                        safeStatus.push_back(strStatusBar[i]);
+                }
+                safeStatus = singleQuote+safeStatus+singleQuote;
+                boost::replace_all(strCmd, "%s", safeStatus);
+
+                if (fThread)
+                    boost::thread t(runCommand, strCmd); // thread runs free
+                else
+                    runCommand(strCmd);
+            }
+        }
     }
 
     printf("accepted alert %d, AppliesToMe()=%d\n", nID, AppliesToMe());