Colin/list repos

lib/App/Multigit.pm

@@ -83,6 +83,7 @@ our %BEHAVIOUR = (
     report_on_no_output => $ENV{MG_REPORT_ON_NO_OUTPUT} // 1,
     ignore_stdout       => !!$ENV{MG_IGNORE_STDOUT},
     ignore_stderr       => !!$ENV{MG_IGNORE_STDERR},
+    list_repos          => $ENV{MG_LIST_REPOS},
     concurrent          => $ENV{MG_CONCURRENT_PROCESSES} // 20,
     skip_readonly       => !!$ENV{MG_SKIP_READONLY},
 );

lib/App/Multigit/Repo.pm

@@ -252,6 +252,8 @@ sub report {
     return Future->done unless $App::Multigit::BEHAVIOUR{report_on_no_output} 
         or $output =~ s/\s//gr;
 
+    $output = '' if $App::Multigit::BEHAVIOUR{list_repos};
+
     return Future->done(
         $dir => $output
     );

script/mg

@@ -25,6 +25,7 @@ sub usage;
         'verbose|v' => sub {
             $qs--;
         },
+        'list|l' => \$ENV{MG_LIST_REPOS},
         'concurrent|c=i' => \$ENV{MG_CONCURRENT_PROCESSES},
         'skip-readonly' => \$ENV{MG_SKIP_READONLY},
     );
@@ -108,4 +109,23 @@ might use this.
 Skip readonly repositories.  Repositories marked readonly = 1 in the .mgconfig
 will be ignored by whatever command you run.
 
+=item -l
+
+=item --list
+
+List repositories that would produce output.  This is useful for piping the list
+of repositories to another mg each.
+
+For example,
+
+    mg -l st -uno | mg each git push
+
+Note that mg grep does a very similar thing and may be more appropriate.
+
+    mg grep git not-master
+
+Is roughly equivalent to,
+
+    mg -lq each git not-master
+
 =back