for-each-repo: run subcommands on configured repos

It can be helpful to store a list of repositories in global or system
config and then iterate Git commands on that list. Create a new builtin
that makes this process simple for experts. We will use this builtin to
run scheduled maintenance on all configured repositories in a future
change.

The test is very simple, but does highlight that the "--" argument is
optional.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 59 insertions, 0 deletions

diff --git a/Documentation/git-for-each-repo.txt b/Documentation/git-for-each-repo.txt
new file mode 100644
index 0000000..94bd19d
--- /dev/null
+++ b/Documentation/git-for-each-repo.txt
@@ -0,0 +1,59 @@
+git-for-each-repo(1)
+====================
+
+NAME
+----
+git-for-each-repo - Run a Git command on a list of repositories
+
+
+SYNOPSIS
+--------
+[verse]
+'git for-each-repo' --config=<config> [--] <arguments>
+
+
+DESCRIPTION
+-----------
+Run a Git command on a list of repositories. The arguments after the
+known options or `--` indicator are used as the arguments for the Git
+subprocess.
+
+THIS COMMAND IS EXPERIMENTAL. THE BEHAVIOR MAY CHANGE.
+
+For example, we could run maintenance on each of a list of repositories
+stored in a `maintenance.repo` config variable using
+
+-------------
+git for-each-repo --config=maintenance.repo maintenance run
+-------------
+
+This will run `git -C <repo> maintenance run` for each value `<repo>`
+in the multi-valued config variable `maintenance.repo`.
+
+
+OPTIONS
+-------
+--config=<config>::
+	Use the given config variable as a multi-valued list storing
+	absolute path names. Iterate on that list of paths to run
+	the given arguments.
++
+These config values are loaded from system, global, and local Git config,
+as available. If `git for-each-repo` is run in a directory that is not a
+Git repository, then only the system and global config is used.
+
+
+SUBPROCESS BEHAVIOR
+-------------------
+
+If any `git -C <repo> <arguments>` subprocess returns a non-zero exit code,
+then the `git for-each-repo` process returns that exit code without running
+more subprocesses.
+
+Each `git -C <repo> <arguments>` subprocess inherits the standard file
+descriptors `stdin`, `stdout`, and `stderr`.
+
+
+GIT
+---
+Part of the linkgit:git[1] suite