Re: [PATCH] report which $PATH entry had trouble running execvp(3)
From: Jeff King <hidden>
Date: 2016-06-15 22:51:04
On Tue, Apr 19, 2011 at 09:01:21PM -0700, Junio C Hamano wrote:
You can add your own custom subcommand 'frotz' to the system by adding 'git-frotz' in a directory somewhere in your $PATH environment variable. When you ask "git frotz" from the command line, "git-frotz" is run via execvp(3). [...] we do not report 'git-frotz' in which directory we had trouble with. We could do better if we implemented the command search behaviour of execvp(3) ourselves.
I like the idea of giving the user more information about which git-frotz was the problem. Usually there is just one, and pointing them to it saves them time. But what about the case of mkdir one two touch one/frotz two/frotz PATH=one:two:$PATH We would report two/frotz, but might it be even better to say "we found 2 frotzes, but neither of them were executable"? I don't know if it is worth the effort for such a weird corner case.
Three plausible scenarios that the execvp(3) would fail for us are: * The first 'git-frotz' found in a directory on $PATH was not a proper executable binary, and we got "Exec format error" (ENOEXEC);
What about the magic "unknown things get executed as shell scripts" behavior that is implemented by libc's execvp? Your patch has a regression for: echo "git log --with-some-options" >local/bin/git-frotz chmod +x local/bin/git-frotz git frotz I have always found that behavior slightly insane, but it is well-established, and your sane_execvp breaks anybody who is depending on it.
quoted hunk ↗ jump to hunk
@@ -278,7 +324,7 @@ fail_pipe: } else if (cmd->use_shell) { execv_shell_cmd(cmd->argv); } else { - execvp(cmd->argv[0], (char *const*) cmd->argv); + cmd->argv[0] = sane_execvp(cmd->argv[0], cmd->argv); } /* * Do not check for cmd->silent_exec_failure; the parent
This is inside "#ifndef WIN32". Presumably people on Windows want it, too. In fact, they already have their own execvp in compat/mingw.c. It might make sense to bring the implementations together. Or perhaps not. Theirs is quite different; it does a search of PATH itself, looking for executables (and magically appending ".exe"), and then exec's the result. On the other hand, doing that PATH lookup, deciding you have something, and _then_ exec'ing can be convenient. IIRC, there are a few warts in the git wrapper that could be improved by doing that, but I don't recall the specifics anymore (maybe something like handling the pager between the momemnt when we decide a command exists and when we exec?). -Peff