[PATCH v2] shell: allow overriding built-in commands

From: Ayman Bagabas <ayman.bagabas@gmail.com>

This patch allows overriding the shell built-in commands by placing a script with the same name under git-shell-commands directory.

This is useful for users who want to extend the shell built-in commands without replacing the original command binary. For instance, a user wanting to allow only a subset of users to run the git-receive-pack can override the command with a script that checks the user and calls the original command if the user is allowed.

Signed-off-by: Ayman Bagabas <ayman.bagabas@gmail.com>
---
    shell: allow overriding built-in commands

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1930%2Faymanbagabas%2Fshell-override-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1930/aymanbagabas/shell-override-v2
Pull-Request: https://github.com/git/git/pull/1930

Range-diff vs v1:

 1:  4fe18878afa ! 1:  60c6339e790 [RFC] shell: allow overriding built-in commands
     @@ Metadata
      Author: Ayman Bagabas <ayman.bagabas@gmail.com>
      
       ## Commit message ##
     -    [RFC] shell: allow overriding built-in commands
     +    shell: allow overriding built-in commands
      
     -    This patch allows overriding built-in commands by placing a script
     -    with the same name under git-shell-commands directory.
     +    This patch allows overriding the shell built-in commands by placing a
     +    script with the same name under git-shell-commands directory.
      
     -    This is useful for users who want to extend the built-in commands
     +    This is useful for users who want to extend the shell built-in commands
          without replacing the original command binary. For instance, a user
     -    wanting to allow only a subset of users to run the git-receive-pack
     -    can override the command with a script that checks the user and
     -    calls the original command if the user is allowed.
     +    wanting to allow only a subset of users to run the git-receive-pack can
     +    override the command with a script that checks the user and calls the
     +    original command if the user is allowed.
      
     -    CC: Junio C Hamano <gitster@pobox.com>, Jeff King <peff@peff.net>
     -    CC: Taylor Blau <me@ttaylorr.com>
          Signed-off-by: Ayman Bagabas <ayman.bagabas@gmail.com>
      
       ## shell.c ##
     @@ shell.c: int cmd_main(int argc, const char **argv)
       		default:
       			continue;
       		}
     --		return cmd->exec(cmd->name, arg);
      +		/* Allow overriding built-in commands */
      +		full_cmd = make_cmd(cmd->name);
      +		if (!access(full_cmd, F_OK)) {
      +			const char *argv[3] = { cmd->name, arg, NULL };
      +			return execv(full_cmd, (char *const *) argv);
     -+		} else {
     -+			return cmd->exec(cmd->name, arg);
      +		}
     + 		return cmd->exec(cmd->name, arg);
       	}
       
      -	cd_to_homedir();

 shell.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)