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

From: "Ayman Bagabas via GitGitGadget" <[email-masked]>
Date: Sun, 23 Mar 2025 00:12:20 +0000

From: Ayman Bagabas <[email-masked]>

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 <[email-masked]>
---
    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 <[email-masked]>
      
       ## 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 <[email-masked]>, Jeff King <[email-masked]>
     -    CC: Taylor Blau <[email-masked]>
          Signed-off-by: Ayman Bagabas <[email-masked]>
      
       ## 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(-)

diff --git a/shell.c b/shell.c
index 76333c80686..76c0157e321 100644
--- a/shell.c
+++ b/shell.c
@@ -194,9 +194,11 @@ int cmd_main(int argc, const char **argv)
 		/* Accept "git foo" as if the caller said "git-foo". */
 		prog[3] = '-';
 
+	cd_to_homedir();
 	for (cmd = cmd_list ; cmd->name ; cmd++) {
 		int len = strlen(cmd->name);
 		char *arg;
+		char *full_cmd;
 		if (strncmp(cmd->name, prog, len))
 			continue;
 		arg = NULL;
@@ -210,10 +212,15 @@ int cmd_main(int argc, const char **argv)
 		default:
 			continue;
 		}
+		/* 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);
+		}
 		return cmd->exec(cmd->name, arg);
 	}
 
-	cd_to_homedir();
 	count = split_cmdline(prog, &user_argv);
 	if (count >= 0) {
 		if (is_valid_cmd_name(user_argv[0])) {

base-commit: 683c54c999c301c2cd6f715c411407c413b1d84e
-- 
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