which.c: C implementation of UNIX which(1)

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Makefile.am

@@ -6,7 +6,7 @@ pkginclude_HEADERS  = lite.h queue.h conio.h tree.h strlite.h strdupa.h strndupa
 libite_la_SOURCES   = chomp.c copyfile.c dir.c fexist.c fisdir.c fmode.c fparseln.c		\
 		      fsendfile.c ifconfig.c lfile.c makepath.c pidfile.c pidfilefn.c		\
 		      progress.c reallocarray.c rsync.c strlcpy.c strlcat.c strtonum.c		\
-		      tempfile.c tree.c
+		      tempfile.c tree.c which.c
 
 libite_la_CPPFLAGS  = -D_GNU_SOURCE
 libite_la_CFLAGS    = -W -Wall -Wextra

README.md

@@ -288,6 +288,11 @@ Generic Functions
   optional listing of file and directory permissions if `show_perms` is
   set.  The `path` argument should be a directory.
 
+- `which(cmd)`
+
+  C implementation of UNIX which(1).  Returns a malloc'ed string with the
+  full path to `cmd` on success, otherwise `NULL`.
+
 
 GNU Functions
 -------------

lite.h

@@ -85,6 +85,8 @@ int     tree(char *path, int show_perms);
 void    progress       (int percent, int max_width);
 void    progress_simple(int percent);
 
+char   *which      (const char *cmd);
+
 #ifndef touch
 #include <sys/stat.h>		/* utimensat() */
 #include <sys/time.h>		/* utimensat() on *BSD */

tests/.gitignore

@@ -14,3 +14,4 @@ rsync
 tempfile
 touch
 tree
+which

tests/Makefile.am

@@ -16,6 +16,7 @@ TESTS          += progress
 TESTS          += rsync
 TESTS          += tempfile
 TESTS          += tree
+TESTS          += which
 
 check_PROGRAMS  = $(TESTS)
 

tests/which.c

@@ -0,0 +1,47 @@
+#include "check.h"
+
+struct tc {
+	char *cmd;
+	int   exp;
+	int   res;
+};
+
+int main(void)
+{
+	int result = 0;
+	size_t i;
+	struct tc test[] = {
+		{ "ls",          1 },
+		{ "free",        1 },
+		{ "modinfo",     1 },
+		{ "useradd",     1 },
+		{ "/etc/passwd", 0 },
+		{ NULL, 0 }
+	};
+
+	for (i = 0; test[i].cmd; i++) {
+		char *path;
+
+		path = which(test[i].cmd);
+		if (!path) {
+			test[i].res = 0;
+			fprintf(stderr, "%20s : Not hot dog\n", test[i].cmd);
+		} else {
+			test[i].res = 1;
+			fprintf(stderr, "%20s : hot dog --> %s\n", test[i].cmd, path);
+			free(path);
+		}
+	}
+
+	for (i = 0; test[i].cmd; i++)
+		result += test[i].exp != test[i].res;
+
+	return result;
+}
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */

which.c

@@ -0,0 +1,89 @@
+/* C implementation of UNIX which(1)
+ *
+ * Copyright (c) 2017  Joachim Nilsson <troglobit@gmail.com>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#include <errno.h>
+#include <stdio.h>		/* snprintf() */
+#include <stdlib.h>		/* realloc(), free() */
+#include <string.h>		/* strtok_r() */
+#include <unistd.h>		/* access() */
+
+/*
+ * Like which(1), returns a malloc'ed path to cmd on success, or NULL
+ */
+char *which(const char *cmd)
+{
+	size_t pathlen = 0;
+	char *ptr, *tok, *env, *path = NULL;
+
+	if (!cmd) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	if (cmd[0] == '/') {
+		path = strdup(cmd);
+		if (!access(path, X_OK))
+			return path;
+
+		if (path)
+			free(path);
+
+		return NULL;
+	}
+
+	ptr = getenv("PATH");
+	if (!ptr)
+		return NULL;
+
+	env = strdup(ptr);
+	if (!env)
+		return NULL;
+
+	tok = strtok_r(env, ":", &ptr);
+	while (tok) {
+		size_t len = strlen(tok) + strlen(cmd) + 2;
+
+		if (pathlen < len) {
+			path = realloc(path, len);
+			if (!path) {
+				free(env);
+				return NULL;
+			}
+			pathlen = len;
+		}
+
+		snprintf(path, pathlen, "%s/%s", tok, cmd);
+		if (!access(path, X_OK)) {
+			free(env);
+			return path;
+		}
+
+		tok = strtok_r(NULL, ":", &ptr);
+	}
+
+	if (path)
+		free(path);
+	free(env);
+
+	return NULL;
+}
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */