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).
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);
* The only 'git-frotz' found in the directories listed on $PATH were not
marked with executable bit, and we got "Permission denied" (EACCES); or
* No 'git-frotz' was found in the directories listed on $PATH, but one of
the directories were unreadable, and we got EACCES.
The first one is easy to understand and to rectify. Most likely, the user
made a typo, either on the command line, or when creating the custom
subcommand. However, the latter two cases are harder to notice, as 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.
Add an internal function sane_execvp() that emulates execvp(3), skipping
ENOENT and EACCES while remembering a path that resulted in EACCES while
trying later directories on $PATH. When failing the request at the end,
report the path that we had trouble with, and use it when reporting the
error.
Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx>
---
Junio C Hamano <gitster@xxxxxxxxx> writes:
>> The following is a tangent that was brought up at $work.
> ...
> We would need to emulate what execvp() does ourselves (i.e. split $PATH,
> prefix each component and try execv(), ignoring ENOENT or EACCES while
> trying next component in $PATH), plus note the first path that got EACCES
> so that we can report which script (including its leading directories) had
> trouble executing. Perhaps a simple enough task for beginners.
run-command.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 47 insertions(+), 1 deletions(-)
diff --git a/run-command.c b/run-command.c
index f91e446..4c95f50 100644
--- a/run-command.c
+++ b/run-command.c
@@ -135,6 +135,52 @@ static int wait_or_whine(pid_t pid, const char *argv0, int silent_exec_failure)
return code;
}
+static const char *sane_execvp(const char *arg0, const char **argv)
+{
+ struct strbuf sb = STRBUF_INIT;
+ struct strbuf failed_path = STRBUF_INIT;
+ char *path = getenv("PATH");
+ char *next;
+
+ if (!path)
+ path = "";
+
+ for (;;) {
+ next = strchrnul(path, ':');
+ if (path < next)
+ strbuf_add(&sb, path, next - path);
+ else
+ strbuf_addch(&sb, '.');
+ if (sb.len && sb.buf[sb.len - 1] != '/')
+ strbuf_addch(&sb, '/');
+ strbuf_addstr(&sb, arg0);
+ execv(sb.buf, (char * const*) argv);
+
+ /*
+ * execvp() skips EACCES and ENOENT and goes on to try
+ * the next entry in the $PATH, but sets errno to EACCES
+ * when it fails at the end.
+ */
+ if (errno == EACCES && !failed_path.len)
+ strbuf_add(&failed_path, sb.buf, sb.len);
+ if (errno != ENOENT) {
+ strbuf_release(&failed_path);
+ return strbuf_detach(&sb, NULL);
+ }
+ strbuf_release(&sb);
+ if (!*next)
+ break;
+ path = next + 1;
+ }
+ if (failed_path.len) {
+ errno = EACCES;
+ return strbuf_detach(&failed_path, NULL);
+ }
+ strbuf_release(&sb);
+ strbuf_release(&failed_path);
+ return arg0;
+}
+
int start_command(struct child_process *cmd)
{
int need_in, need_out, need_err;
@@ -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
--
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