Add '$' for keeping selections that passes a shell command

'$' pipes each selections through a given shell command, and
only keeps the one that have an exit code of 0

Fixes #36

README.asciidoc

@@ -303,6 +303,9 @@ _alt-k_ allows you to enter a regex and keep only the selections that
 contains a match for this regex. using _alt-K_ you can keep the selections
 not containing a match.
 
+_$_ allows you to enter a shell command and pipe each selections to it.
+Selections whose shell command returns 0 will be kept, other will be dropped.
+
 Object Selection
 ----------------
 

doc/keymap

@@ -1,5 +1,5 @@
 ┌───────┬───────┬───────┬───────┬───────┬───────┬───────┬───────┬───────┬───────┬───────┬───────┬───────┲━━━━━━━━━━━━━━┓
-│  upper│       │convtab│       │       │sel all│       │  align│pattern│       │       │       │       ┃ ⇤            ┃
+│  upper│       │convtab│       │selpipe│sel all│       │  align│pattern│       │       │       │       ┃ ⇤            ┃
 ├┄┄CASE┄┼┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┨              ┃
 │  lower│ 1     │ 2     │ 3     │ 4     │ 5     │ 6     │ 7     │ 8     │ 9     │ 0     │       │       ┃              ┃
 ┢━━━━━━━┷━━━┱───┴───┬───┴───┬───┴───┬───┴───┬───┴───┬───┴───┬───┴───┬───┴───┬───┴───┬───┴───┬───┴───┬───┺━━━┳━━━━━━━━━━┫

src/normal.cc

@@ -791,6 +791,29 @@ void keep(Context& context, int)
     });
 }
 
+void keep_pipe(Context& context, int)
+{
+    context.input_handler().prompt(
+        "keep pipe:", "", get_color("Prompt"), shell_complete,
+        [](const String& cmdline, PromptEvent event, Context& context) {
+            if (event != PromptEvent::Validate)
+                return;
+            const Buffer& buffer = context.buffer();
+            auto& shell_manager = ShellManager::instance();
+            SelectionList keep;
+            for (auto& sel : context.selections())
+            {
+                int status = 0;
+                shell_manager.pipe(content(buffer, sel), cmdline, context,
+                                   {}, EnvVarMap{}, &status);
+                if (status == 0)
+                    keep.push_back(sel);
+            }
+            if (keep.empty())
+                throw runtime_error("no selections remaining");
+            context.selections() = std::move(keep);
+    });
+}
 template<bool indent_empty = false>
 void indent(Context& context, int)
 {
@@ -1405,6 +1428,7 @@ KeyMap keymap =
 
     { alt('k'), keep<true> },
     { alt('K'), keep<false> },
+    { '$', keep_pipe },
 
     { '<', deindent<true> },
     { '>', indent<false> },

src/shell_manager.cc

@@ -18,15 +18,17 @@ ShellManager::ShellManager()
 
 String ShellManager::eval(StringView cmdline, const Context& context,
                           memoryview<String> params,
-                          const EnvVarMap& env_vars)
+                          const EnvVarMap& env_vars,
+                          int* exit_status)
 {
-    return pipe("", cmdline, context, params, env_vars);
+    return pipe("", cmdline, context, params, env_vars, exit_status);
 }
 
 String ShellManager::pipe(StringView input,
                           StringView cmdline, const Context& context,
                           memoryview<String> params,
-                          const EnvVarMap& env_vars)
+                          const EnvVarMap& env_vars,
+                          int* exit_status)
 {
     int write_pipe[2]; // child stdin
     int read_pipe[2];  // child stdout
@@ -66,7 +68,14 @@ String ShellManager::pipe(StringView input,
         if (not errorout.empty())
             write_debug("shell stderr: <<<\n" + errorout + ">>>");
 
-        waitpid(pid, nullptr, 0);
+        waitpid(pid, exit_status, 0);
+        if (exit_status)
+        {
+            if (WIFEXITED(*exit_status))
+                *exit_status = WEXITSTATUS(*exit_status);
+            else
+                *exit_status = -1;
+        }
     }
     else try
     {

src/shell_manager.hh

@@ -18,12 +18,14 @@ public:
 
     String eval(StringView cmdline, const Context& context,
                 memoryview<String> params,
-                const EnvVarMap& env_vars);
+                const EnvVarMap& env_vars,
+                int* exit_status = nullptr);
 
     String pipe(StringView input,
                 StringView cmdline, const Context& context,
                 memoryview<String> params,
-                const EnvVarMap& env_vars);
+                const EnvVarMap& env_vars,
+                int* exit_status = nullptr);
 
     void register_env_var(StringView regex, EnvVarRetriever retriever);