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diff --git a/lib/Git/Annex/BatchCommand.pm b/lib/Git/Annex/BatchCommand.pm
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+# Git::Annex
+# Perl interface to git-annex repositories
+#
+# Copyright (C) 2020  Sean Whitton <spwhitton@spwhitton.name>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or (at
+# your option) any later version.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+=head1 NAME
+
+Git::Annex::BatchCommand - Perl interface to git-annex --batch commands
+
+=head1 SYNOPSIS
+
+  # you should not instantiate this class yourself; use Git::Annex::batch
+  my $annex = Git::Annex->new("/home/spwhitton/annex");
+  my $batch = $annex->batch("find", "--not", "--in=here");
+
+  # see git-annex-find(1) -- `git annex find --batch --not --in here`
+  # prints an empty string for each file which is not present
+  say "foo/bar is not present in this repo" if $batch->say("foo/bar");
+
+=head1 DESCRIPTION
+
+This class can be used to run git-annex commands which take the
+C<--batch> option.  You can feed the command lines of input and you
+will get back git-annex's responses.
+
+The main point of using C<--batch> commands from Perl is to keep
+git-annex running rather than repeatedly executing new git-annex
+processes to perform queries or request changes.
+
+=cut
+
+package Git::Annex::BatchCommand;
+
+use 5.028;
+use strict;
+use warnings;
+
+use autodie;
+use Carp;
+use IPC::Open2;
+
+=head1 METHODS
+
+=head1 new($annex, $cmd, @args)
+
+Initialise a batch process in Git::Annex C<$annex>, running git-annex
+subcommand C<$cmd> (e.g. C<setpresentkey>) with arguments C<@args>.
+
+You should use Git::Annex::batch in preference to this method.
+
+=cut
+
+sub new {
+    my (undef, $annex, $cmd, @params) = @_;
+    croak "not enough arguments to Git::Annex::BatchCommand constructor"
+      unless $annex and $cmd;
+
+    # normalise supplied arguments a little
+    unshift @params, "--batch" unless grep /\A--batch\z/, @params;
+
+    my $self = bless { _annex => $annex, _cmd => [$cmd, @params] }
+      => "Git::Annex::BatchCommand";
+    $self->_spawn;
+    return $self;
+}
+
+=head2 say($input, ...)
+
+Say a line or lines of input to the batch command's standard input.
+Trailing line breaks in C<$input> are optional.
+
+In list context, returns a list of chomped git-annex's responses to
+the items of input, chomped.  In scalar context, returns the number of
+trueish responses.
+
+=cut
+
+sub say {
+    my ($self, @input) = @_;
+    my @output;
+    for (@input) {
+        chomp;
+        say { $self->{_in} } $_;
+        chomp(my $out = readline $self->{_out});
+        push @output, $out;
+    }
+    return wantarray ? @output : scalar @output;
+}
+
+=head2 restart
+
+Kill and restart the C<--batch> command.
+
+This is sometimes needed to ensure the C<--batch> command picks up
+changes made to the git-annex branch.
+
+=cut
+
+sub restart {
+    my $self = shift;
+    $self->_despawn;
+    $self->_spawn;
+}
+
+sub _spawn {
+    my $self = shift;
+    my ($out, $in);
+    $self->{_pid} = open2 $out, $in, "git",
+      "-C", $self->{_annex}->toplevel,
+      "annex", @{ $self->{_cmd} };
+    ($self->{_out}, $self->{_in}) = ($out, $in);
+}
+
+sub _despawn {
+    my $self = shift;
+    close $self->{_in};
+    close $self->{_out};
+    # reap the child per IPC::Open2 docs
+    waitpid $self->{_pid}, 0;
+}
+
+sub DESTROY { local($., $@, $!, $^E, $?); shift->_despawn }
+
+1;