* RE: Cygwin's execlp() does not work with an empty $PATH element
2022-06-26 15:09 Cygwin's execlp() does not work with an empty $PATH element Lavrentiev, Anton (NIH/NLM/NCBI) [C]
@ 2022-06-26 16:26 ` Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2022-06-27 11:16 ` Takashi Yano
1 sibling, 0 replies; 4+ messages in thread
From: Lavrentiev, Anton (NIH/NLM/NCBI) [C] @ 2022-06-26 16:26 UTC (permalink / raw)
To: 'cygwin@cygwin.com'
There's another discrepancy for execlp() on Cygwin. In the absence of the PATH environment, it should consider the current directory first, then look up somewhere else.
And it does so on Linux! Not on Cygwin, though. Please take a look below:
Linux:
$ ./hello
exec: No such file or directory
$ unset PATH
$ echo $PATH
$ ./hello
Hello
Cygwin:
$ ./hello
exec: No such file or directory
$ unset PATH
$ echo $PATH
$ ./hello
exec: No such file or directory
Anton Lavrentiev
Contractor NIH/NLM/NCBI
> -----Original Message-----
> From: Cygwin <cygwin-bounces+lavr=ncbi.nlm.nih.gov@cygwin.com> On Behalf Of Lavrentiev,
> Anton (NIH/NLM/NCBI) [C] via Cygwin
> Sent: Sunday, June 26, 2022 11:10 AM
> To: 'cygwin@cygwin.com' <cygwin@cygwin.com>
> Subject: [EXTERNAL] Cygwin's execlp() does not work with an empty $PATH element
>
> Hi all,
>
> An empty PATH element (":xxx" or "xxx::xxx" or "xxx:") is to be considered as the current
> directory (from the very first days of Unix).
>
> However, Cygwin does not seem to obey the rule.
>
> Consider the following simple C program:
>
> $ cat hello.c
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <unistd.h>
>
> int main(int argc, const char* argv[])
> {
> if (argc < 2) {
> const char* prog = strrchr(argv[0], '/');
> if (!prog++)
> prog = argv[0];
> execlp(prog, prog, "Hello", NULL); // execute just by the program name
> perror("exec");
> return 1;
> }
> printf("%s\n", argv[1]);
> return 0;
> }
>
> Now compare the execution on Linux and Cygwin:
>
> Linux:
>
> $ gcc -Wall -o hello hello.c
> $ hello
> bash: hello: command not found
> $ ./hello
> exec: No such file or directory
> $ PATH=".:$PATH" ./hello
> Hello
> $ PATH=":$PATH" ./hello
> Hello
> $ PATH="${PATH}:" ./hello
> Hello
>
> Cygwin:
>
> $ gcc -Wall -o hello hello.c
> $ hello
> -bash: hello: command not found
> $ ./hello
> exec: No such file or directory
> $ PATH=".:$PATH" ./hello
> Hello
> $ PATH=":$PATH" ./hello
> exec: No such file or directory
> $ PATH="${PATH}:" ./hello
> exec: No such file or directory
>
> As you can see, the execution failed when an empty PATH element was added on Cygwin
> (yet it was perfectly fine on Linux).
>
> Anton Lavrentiev
> Contractor NIH/NLM/NCBI
>
>
> --
> Problem reports:
> https://gcc02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcygwin.com%2Fproblems.ht
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Cygwin's execlp() does not work with an empty $PATH element
2022-06-26 15:09 Cygwin's execlp() does not work with an empty $PATH element Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2022-06-26 16:26 ` Lavrentiev, Anton (NIH/NLM/NCBI) [C]
@ 2022-06-27 11:16 ` Takashi Yano
2022-06-27 12:15 ` Takashi Yano
1 sibling, 1 reply; 4+ messages in thread
From: Takashi Yano @ 2022-06-27 11:16 UTC (permalink / raw)
To: cygwin
On Sun, 26 Jun 2022 15:09:34 +0000
"Lavrentiev, Anton \(NIH/NLM/NCBI\) \[C\] wrote:
> An empty PATH element (":xxx" or "xxx::xxx" or "xxx:") is to be considered as the current directory (from the very first days of Unix).
>
> However, Cygwin does not seem to obey the rule.
>
> Consider the following simple C program:
>
> $ cat hello.c
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <unistd.h>
>
> int main(int argc, const char* argv[])
> {
> if (argc < 2) {
> const char* prog = strrchr(argv[0], '/');
> if (!prog++)
> prog = argv[0];
> execlp(prog, prog, "Hello", NULL); // execute just by the program name
> perror("exec");
> return 1;
> }
> printf("%s\n", argv[1]);
> return 0;
> }
>
> Now compare the execution on Linux and Cygwin:
>
> Linux:
>
> $ gcc -Wall -o hello hello.c
> $ hello
> bash: hello: command not found
> $ ./hello
> exec: No such file or directory
> $ PATH=".:$PATH" ./hello
> Hello
> $ PATH=":$PATH" ./hello
> Hello
> $ PATH="${PATH}:" ./hello
> Hello
>
> Cygwin:
>
> $ gcc -Wall -o hello hello.c
> $ hello
> -bash: hello: command not found
> $ ./hello
> exec: No such file or directory
> $ PATH=".:$PATH" ./hello
> Hello
> $ PATH=":$PATH" ./hello
> exec: No such file or directory
> $ PATH="${PATH}:" ./hello
> exec: No such file or directory
>
> As you can see, the execution failed when an empty PATH element was added on Cygwin
> (yet it was perfectly fine on Linux).
How about the following patch?
diff --git a/winsup/cygwin/spawn.cc b/winsup/cygwin/spawn.cc
index e0f1247e1..8fe9d089f 100644
--- a/winsup/cygwin/spawn.cc
+++ b/winsup/cygwin/spawn.cc
@@ -118,8 +118,10 @@ find_exec (const char *name, path_conv& buf, const char *search,
the name of an environment variable. */
if (strchr (search, '/'))
*stpncpy (tmp, search, NT_MAX_PATH - 1) = '\0';
- else if (has_slash || isdrive (name) || !(path = getenv (search)) || !*path)
+ else if (has_slash || isdrive (name))
goto errout;
+ else if (!(path = getenv (search)) || !*path)
+ strcpy (tmp, "."); /* Search the current directory when PATH is absent */
else
*stpncpy (tmp, path, NT_MAX_PATH - 1) = '\0';
@@ -134,7 +136,9 @@ find_exec (const char *name, path_conv& buf, const char *search,
already tried that. */
if ((opt & FE_CWD) && (tmp_path[0] == '\0'
|| (tmp_path[0] == '.' && tmp_path[1] == '\0')))
- continue;
+ goto next;
+ else if (tmp_path[0] == '\0') /* An empty path means the current dir. */
+ eotmp = stpcpy (tmp_path, ".");
*eotmp++ = '/';
stpcpy (eotmp, name);
@@ -146,7 +150,7 @@ find_exec (const char *name, path_conv& buf, const char *search,
if ((suffix = perhaps_suffix (tmp_path, buf, err1, opt)) != NULL)
{
if (buf.has_acls () && check_file_access (buf, X_OK, true))
- continue;
+ goto next;
/* Overwrite potential symlink target with original path.
See comment preceeding this method. */
buf.set_posix (tmp_path);
@@ -154,8 +158,13 @@ find_exec (const char *name, path_conv& buf, const char *search,
goto out;
}
+next:
+ if (*path == '\0')
+ break;
+ if (*path == ':')
+ path++;
}
- while (*path && *++path);
+ while (true);
errout:
/* Couldn't find anything in the given path.
--
Takashi Yano <takashi.yano@nifty.ne.jp>
^ permalink raw reply [flat|nested] 4+ messages in thread