Hi Paul,
> Without this change it's impossible for a program to show the correct
> error message when the program is found on the path, but is not
> executable.
Good point!
I've committed a slightly different patch, based on yours. While your
patch was fully correct, I have different preferences:
- You don't need a dependency to the 'errno' module, because
(see doc/posix-headers/errno.texi) it is only needed for more
"advanced" errno values. For the basic ones like ENOENT, EINVAL,
EACCES, etc. no portability problems are known.
- Since the errno value is a saved one in some cases, but not in
all cases, I prefer a variable name 'failure_errno' to 'saved_errno'.
- In the specification comment in findprog.h: I avoid explaining the
algorithm that a certain function employs. Only: what are the inputs?
what are the outputs? and only the minimal necessary information about
the inner workings of the function.
It must be possible to describe a function in an abstract way. If I
was led to document the algorithm that a function uses, this would
be a sign that the function is not well designed.
2019-09-15 Paul Smith <psm...@gnu.org>
Bruno Haible <br...@clisp.org>
findprog-in: Set errno when the search fails.
* lib/findprog-in.c: Include <errno.h>.
(find_in_given_path): Set errno before returning NULL.
* lib/findprog.h (find_in_given_path): Update comment accordingly.
Define the term "slash".
diff --git a/lib/findprog-in.c b/lib/findprog-in.c
index d601e06..5e90680 100644
--- a/lib/findprog-in.c
+++ b/lib/findprog-in.c
@@ -21,6 +21,7 @@
/* Specification. */
#include "findprog.h"
+#include <errno.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
@@ -98,6 +99,7 @@ find_in_given_path (const char *progname, const char *path,
{
/* Try the various suffixes and see whether one of the files
with such a suffix is actually executable. */
+ int failure_errno;
size_t i;
#if defined _WIN32 && !defined __CYGWIN__ /* Native Windows */
const char *progbasename;
@@ -113,6 +115,7 @@ find_in_given_path (const char *progname, const char *path,
#endif
/* Try all platform-dependent suffixes. */
+ failure_errno = ENOENT;
for (i = 0; i < sizeof (suffixes) / sizeof (suffixes[0]); i++)
{
const char *suffix = suffixes[i];
@@ -143,10 +146,14 @@ find_in_given_path (const char *progname, const char
*path,
return progpathname;
}
+ if (errno != ENOENT)
+ failure_errno = errno;
+
free (progpathname);
}
}
+ errno = failure_errno;
return NULL;
}
}
@@ -158,11 +165,13 @@ find_in_given_path (const char *progname, const char
*path,
path = "";
{
+ int failure_errno;
/* Make a copy, to prepare for destructive modifications. */
char *path_copy = xstrdup (path);
char *path_rest;
char *cp;
+ failure_errno = ENOENT;
for (path_rest = path_copy; ; path_rest = cp + 1)
{
const char *dir;
@@ -222,6 +231,9 @@ find_in_given_path (const char *progname, const char *path,
return progpathname;
}
+ if (errno != ENOENT)
+ failure_errno = errno;
+
free (progpathname);
}
}
@@ -232,7 +244,8 @@ find_in_given_path (const char *progname, const char *path,
/* Not found in PATH. */
free (path_copy);
- }
- return NULL;
+ errno = failure_errno;
+ return NULL;
+ }
}
diff --git a/lib/findprog.h b/lib/findprog.h
index f7b4407..804f02a 100644
--- a/lib/findprog.h
+++ b/lib/findprog.h
@@ -36,19 +36,29 @@ extern "C" {
extern const char *find_in_path (const char *progname);
/* Looks up a program in the given PATH-like string.
+
The PATH argument consists of a list of directories, separated by ':' or
(on native Windows) by ';'. An empty PATH element designates the current
directory. A null PATH is equivalent to an empty PATH, that is, to the
singleton list that contains only the current directory.
+
Determines the pathname that would be called by execlp/execvp of PROGNAME.
- If successful, it returns a pathname containing a slash (either absolute
or relative to the current directory). The returned string can be used
with either execl/execv or execlp/execvp. It is freshly malloc()ed if it
is != PROGNAME.
- - Otherwise, it returns NULL.
+ - Otherwise, it sets errno and returns NULL.
+ Specific errno values include:
+ - ENOENT: means that the program's file was not found.
+ - EACCESS: means that the program's file was found but lacks the
+ execute permissions.
If OPTIMIZE_FOR_EXEC is true, the function saves some work, under the
assumption that the resulting pathname will not be accessed directly,
- only through execl/execv or execlp/execvp. */
+ only through execl/execv or execlp/execvp.
+
+ Here, a "slash" means:
+ - On POSIX systems excluding Cygwin: a '/',
+ - On Windows, OS/2, DOS platforms: a '/' or '\'. */
extern const char *find_in_given_path (const char *progname, const char *path,
bool optimize_for_exec);
