Git::Repository::Tutorial(3)

NAME
Git::Repository::Tutorial - Control git from Perl using Git::Repository

SYNOPSIS
    use Git::Repository;

    # do cool stuff with Git, using the following advice

HOW-TO
A Git::Repository object represents an actual Git repository, against which you can run commands.

  Obtain a Git::Repository object from an existing repository
If your script is expected to run against a repository in the current directory (like most Git commands), let Git::Repository handle the magic:

    $r = Git::Repository->new();

If the repository has a working copy (work tree):

    $r = Git::Repository->new( work_tree => $dir );

If the repository is a bare repository, or you prefer to provide the .git directory location:

    $r = Git::Repository->new( git_dir => $gitdir );

If the work tree and the git directory are in unrelated locations, you can also provide both:

    $r = Git::Repository->new( work_tree => $dir, git_dir => $gitdir );

The constructor also accepts an option hash. The various options are detailed in the manual page for Git::Repository::Command.

  Run any git command
Git commands can be run against an existing Git::Repository object, or against the class itself (in which case, git will try to deduce its context from the current directory and the environment).

The pattern for running commands is always the same:

    $r->run( $command => @arguments, \%options );

The $command and @arguments are identical to those you'd pass to the "git" command-line tool. The options hash contains options, as described in the manual page for Git::Repository::Command.

  Create a new repository
Sometime, you'll need to create the Git repository from scratch:

    # git version 1.6.5 and above
    Git::Repository->run( init => $dir );
    $r = Git::Repository->new( work_tree => $dir );

Any git older than 1.6.5 requires the command to be run in the work tree, so we use the "cwd" option:

    # git version 1.5.0.rc1 and above
    Git::Repository->run( init => { cwd => $dir } );
    $r = Git::Repository->new( work_tree => $dir );

    # older git versions
    Git::Repository->run( 'init-db' => { cwd => $dir } );
    $r = Git::Repository->new( work_tree => $dir );

Note that the old "create()" method is obsolete (as of Git::Repository 1.18, from April 16, 2011) and has been removed (as of Git::Repository 1.301, January 21, 2013).

  Clone a repository
Cloning works the same way:

    Git::Repository->run( clone => $url => $dir );
    $r = Git::Repository->new( work_tree => $dir );

  Run a simple command
When you don't really care about the output of the command, just call it:

    $r->run( add => '.' );
    $r->run( commit => '-m', 'my commit message' );

In case of an error or warning, Git::Repository will "croak()" or "carp()" appropriately.

  Properly quote options
It's common to work out the proper string of Git commands needed to achieve your goal in the shell, before actually turning them into calls to "Git::Repository->run".

Some options might require quoting, to properly get the arguments to Git through the shell:

    # shell
    $ git log --since='Fri Jul 26 19:34:15 2013 +0200' --grep='report ticket'

Such quoting is of course not needed with Git::Repository:

    $since = 'Fri Jul 26 19:34:15 2013 +0200';
    $grep  = 'report ticket';
    my $cmd = $r->command( log => "--since=$since", "--grep=$grep" );

  Silence warnings for some Git commands
Some Git porcelain commands provide additional information on "STDERR". One typical example is "git checkout":

    $ git checkout mybranch
    Switched to branch 'mybranch'

The "run()" method of Git::Repository treats all output on "STDERR" as a warning. Therefore, the following code:

    $r->run( checkout => 'mybranch' );

will output a warning like this one:

    Switched to branch 'mybranch' at myscript.pl line 10.

In such a case, you can use the "quiet" option to silence the warning for a single command:

    $r->run( checkout => 'mybranch', { quiet => 1 } );

To silence all warnings, you can pass the "quiet" option during the creation of the original repository object:

    my $r = Git::Repository->new( { quiet => 1 } );

This is not recommended, as it might hide important information from you.

  Process normal and error output
The "run()" command doesn't capture "STDERR": it only warns (or dies) if something was printed on it. To be able to actually capture error output, "command()" must be used.

    my $cmd = $r->command( @cmd );
    my @errput = $cmd->stderr->getlines();
    $cmd->close;

"run()" also captures all output at once, which can lead to unnecessary memory consumption when capturing the output of some really verbose commands.

    my $cmd = $r->command( log => '--pretty=oneline', '--all' );
    my $log = $cmd->stdout;
    while (<$log>) {
        ...;
    }
    $cmd->close;

Of course, as soon as one starts reading and writing to an external process' communication handles, a risk of blocking exists. Caveat emptor.

  Provide input on standard input
Use the "input" option:

    my $commit = $r->run( 'commit-tree', $tree, '-p', $parent,
        { input => $message } );

  Change the environment of a command
Use the "env" option:

    $r->run(
        'commit', '-m', 'log message',
        {   env => {
                GIT_COMMITTER_NAME  => 'Git::Repository',
                GIT_COMMITTER_EMAIL => 'book@cpan.org',
            },
        },
    );

See Git::Repository::Command for other available options.

  Ignore the system and global configuration files
Git has three levels of configuration files that can change the output of porcelain commands: system ($(prefix)/etc/gitconfig), global ($HOME/.gitconfig and $XDG_CONFIG_HOME/git/config) and local (.git/config inside the repository).

To ensure the system and global configuration files will be ignored and won't interfere with the expected output of your Git commands, you can add the following keys to the "env" option:

    GIT_CONFIG_NOSYSTEM => 1,
    XDG_CONFIG_HOME     => undef,
    HOME                => undef,

  Ensure the output from Git commands is not localized
Since version 1.7.9, Git translates its most common interface messages into the user's language if translations are available and the locale is appropriately set.

This means that naively parsing the output "porcelain" commands might fail if the program is unexpectedly run under an unexpected locale.

The easiest way to ensure your Git commands will be run in a "locale-safe" environment, is to set the "LC_ALL" environment variable to "C".

The brutal way:

    $ENV{LC_ALL} = 'C';

The temporary way:

    local $ENV{LC_ALL} = 'C';

The subtle way (restricted to the commands run on a given Git::Repository instance):

    my $r = Git::Repository->new( { env => { LC_ALL => 'C' } } );

The stealthiest way (restricted to a single command):

    $r->run( ..., { env => { LC_ALL => 'C' } } );

  Ensure the Git commands are run from the current working directory
By default, Git::Repository::Command will "chdir()" to the root of the work tree before launching the requested Git command.

This means that no matter where your program "chdir()" to, commands on the Git::Repository instance will by default be run from the root of the work tree. So, commands such as "add" need to use the "full" path (relative to "GIT_WORK_TREE") of the files to be added.

The "cwd" option can be used to define where Git::Repository::Command will "chdir()" to. To instruct Git::Repository::Command to not "chdir()" (and therefore run the Git command from the current working directory), set the option to "undef":

    # run from cwd for this command only
    $r->run( ..., { cwd => undef } );

    # always run git from cwd
    my $r = Git::Repository->new( { cwd => undef } );

  Finely control when "run()" dies
By default, "Git::Repository->run( ... )" dies if the Git command exited with a status code of 128 (fatal error) or 129 (usage message).

Some commands will throw an error and exit with a status different from the previous two:

    $r->run( checkout => 'does-not-exist' );    # exit status: 1

The above "run()" call does not die, and output the following warning:

    error: pathspec 'does-not-exist' did not match any file(s) known to git.

The exit status (as given by "$? >> 8") is 1.

To force "run()" to die when the Git command exits with status 1, use the "fatal" option (added in version 1.304, May 25, 2013):

    $r->run( checkout => 'does-not-exist', { fatal => 1 } );

By default, 128 and 129 remain in the list of fatal codes.

Here are a few examples:

    # set the fatal codes for all call to run() on this object
    $r = Git::Repository->new( { fatal => [ 1 .. 255 ] } );

As usual, setting the option to the Git::Repository object will set it for all commands run for it:

    # "!0" is a shortcut for 1 .. 255
    $r = Git::Repository->new( { fatal => [ "!0" ] } );

Using negative codes will make these values non-fatal:

    # the above call to new() makes all exit codes fatal
    # but 3 and 7 won't be fatal for this specific run
    $r->run( ..., { fatal => [ -3, -7 ] } );

When the list contains a single item, there is no need to use an array reference:

    # same as [ "!0" ]
    $r = Git::Repository->new( { fatal => "!0" } );

    # remove 17 from the list of fatal exit codes for this run only
    $r->run( ..., { fatal => -17 } );

See Git::Repository::Command for other available options.

  Process the output of git log
When creating a tool that needs to process the output of git log, you should always define precisely the expected format using the --pretty option, and choose a format that is easy to parse.

Assuming git log will output the default format will eventually lead to problems, for example when the user's git configuration defines "format.pretty" to be something else than the default of "medium".

See also Git::Repository::Plugin::Log for adding to your Git::Repository objects a "log()" method that will parse the log output for you.

Understanding the various options for git log can make it very simple to obtain a lot of information.

For example:

    # all tags reachable from $committish
    my @tags = map {
        s/^ \((.*)\)/$1/;
        ( map +( split /: / )[1], grep /^tag: /, split /, / )
      }
      $_->run( qw( log --simplify-by-decoration --pretty=%d ), $committish );

  Process the output of git shortlog
git shortlog behaves differently when it detects it's not attached to a terminal. In that case, it just tries to read some git log output from its standard input.

So this oneliner will hang, because git shortlog is waiting for some data from the program connected to its standard input (the oneliner):

    perl -MGit::Repository -le 'print scalar Git::Repository->run( shortlog => -5 )'

Whereas this one will "work" (as in "immediately return with no output"):

    perl -MGit::Repository -le 'print scalar Git::Repository->run( shortlog => -5, { input => "" } )'

So, you need to give git shortlog some input (from git log):

    perl -MGit::Repository -le 'print scalar Git::Repository->run( shortlog => { input => scalar Git::Repository->run( log => -5 ) } )'

If the log output is large, you'll probably be better off with something like the following:

    use Git::Repository;

    # start both git commands
    my $log = Git::Repository->command('log')->stdout;
    my $cmd = Git::Repository->command( shortlog => -ens );

    # feed one with the output of the other
    my $in = $cmd->stdin;
    print {$in} $_ while <$log>;
    close $in;

    # and do something with the output
    print $cmd->stdout->getlines;

  Wrap git in a sudo call
If for a given repository you want to wrap all calls to git in a "sudo" call, you can use the "git" option with an array ref:

    my $r = Git::Repository->new( { git => [qw( sudo -u nobody git )] } );

In this case, every call to git from $r will actually call "sudo -u nobody git".

  Use submodules
Because Git::Repository automatically sets the "GIT_DIR" and "GIT_WORK_TREE" environment variables, some "submodule" sub-commands may fail. For example:

    $r->run( submodule => add => $repository => 'sub' );

will give the following error:

    error: pathspec 'sub' did not match any file(s) known to git.

To avoid this error, you should enforce the removal of the "GIT_WORK_TREE" variable from the environment in which the command is run:

    $r->run(
        submodule => add => $repository => 'sub',
        { env => { GIT_WORK_TREE => undef } }
    );

Note that System::Command version 1.04 is required to be able to remove variables from the environment.

  Sort git versions
Basically, you need to recreate the "cmp" operator for Git versions, using the private "_version_gt()" method (which accepts two parameters):

    @sorted_versions = sort {
        Git::Repository::_version_gt( $a, $b )
            || -Git::Repository::_version_gt( $b, $a )
    } @versions;

  Add specialized methods to your Git::Repository objects
Have a look at Git::Repository::Plugin and Git::Repository::Plugin::Log, to learn how to add your own methods to Git::Repository.

  Run code on the output of a git command, and get the results
Sometimes you need to process the output of a command, by running a callback on each line of the output.

    # code inspiration:
    # https://github.com/dolmen/github-keygen/blob/24c501072ba7d890810de3008434c1fe1f757286/release.pl#L178

    my %tree;
    $r->run( 'ls-tree' => $commit, sub {
        my ($mode, $type, $object, $file) = split;
        $tree{$file} = [ $mode, $type, $object ];
    } );

Note that the value returned by the callback will be returned as part of the "run()" output, instead of the original line.

COPYRIGHT
Copyright 2010-2016 Philippe Bruhat (BooK), all rights reserved.

LICENSE
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.