add which

which.c

@@ -0,0 +1,80 @@
+#include <sys/stat.h>
+
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "arg.h"
+#include "util.h"
+
+static int aflag;
+
+static int
+which(const char *path, const char *name)
+{
+	char file[PATH_MAX], *p, *s, *ptr;
+	size_t len;
+	struct stat st;
+	int found = 0;
+
+	p = ptr = estrdup(path);
+	for (s = p; (s = strsep(&p, ":")); ) {
+		if (!s[0])
+			s = ".";
+		len = strlen(s);
+
+		if (snprintf(file, sizeof(file), "%s%s%s",
+			s,
+			len > 0 && s[len - 1] != '/' ? "/" : "",
+			name) >= sizeof(file))
+			eprintf("path too long\n");
+
+		if (stat(file, &st) == 0 && S_ISREG(st.st_mode) &&
+		    access(file, X_OK) == 0) {
+			found = 1;
+			puts(file);
+			if (!aflag)
+				break;
+		}
+	}
+	free(ptr);
+
+	return found;
+}
+
+static void
+usage(void)
+{
+	eprintf("usage: %s [-a] name...\n", argv0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	char *path;
+	int i, found;
+
+	ARGBEGIN {
+	case 'a':
+		aflag = 1;
+		break;
+	default:
+		usage();
+	} ARGEND;
+
+	if (!argc)
+		usage();
+
+	if (!(path = getenv("PATH")))
+		eprintf("$PATH not set\n");
+
+	for (i = 0, found = 0; i < argc; i++) {
+		if (which(path, argv[i]))
+			found++;
+		else
+			weprintf("%s: Command not found.\n", argv[i]);
+	}
+	return !found ? 2 : found == argc ? 0 : 1;
+}