more cleaning

libshell/getpaths.3

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+.TH GETPATHS 3
+
+.SH NAME
+getpaths \- get an array of the current executable PATHs
+
+.SH LIBRARY
+libshell
+
+.SH SYNOPSIS
+.In stdlib.h
+.In string.h
+.In libshell.h
+.Ft char **
+.Fn getpaths void
+
+.SH DESCRIPTION
+.Fn getpaths
+returns the system PATHs as an array of null-terminated strings ordered from highest to lowest priority.
+The last address in the array is NULL.
+The first address in the array, and the array address itself, should be passed to
+.Xr free 3
+to release the allocated storage when the returned array is no longer needed.
+
+.SH EXAMPLES
+To print the current PATHs, from highest to lowest priority:
+.Bd -literal -offset indent
+#include <stdlib.h>
+#include <string.h>
+#include <libshell.h>
+int main(){
+    char **paths;
+    int i;
+    paths = getpaths();
+    if(paths == NULL)
+        exit(EXIT_FAILURE);
+    for(i = 0; paths[i] != NULL; ++i)
+        printf("%s\n", paths[i]);
+    free(*paths);
+    free(paths);
+    return EXIT_SUCCESS;
+}
+.Ed
+
+.SH SEE ALSO
+.Xr getenv 3
+
+.SH STANDARDS
+.Fn getpaths
+is not part of any current standard.
+
+.SH BUGS
+Certainly existent but not yet known.

libshell/libshell.c

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+#include "libshell.h"
+
+char **
+getpaths(void)
+{
+	char *p;
+	char **q;
+	char *path;
+	size_t path_s;
+	char *path_temp;
+	char **paths;
+	size_t paths_s;
+
+	if((path_temp = getenv(PATH_NAME)) == NULL){
+		errno = ENOMEM; /* Cannot allocate memory */
+		return NULL;
+	}
+
+	/* How long is path? */
+	for(path_s = 0; path_temp[path_s] != '\0'; ++path_s);
+	/* path_s has the size of the path string, not including the null
+	 * terminator */
+
+	/* getenv's return value mustn't be modified so copy it into memory we
+	 * control */
+	if((path = malloc(sizeof(char) * (path_s + 1))) == NULL){
+		errno = ENOMEM; /* Cannot allocate memory */
+		return NULL;
+	}
+	memcpy(path, path_temp, path_s + 1);
+	path_temp = NULL;
+	path_s = 0; /* This shouldn't be necessary anymore */
+
+	/* How many paths in $PATH? */
+	for(paths_s = 1, p = path; *p != '\0'; paths_s += *p++ == PATH_DELIMITER);
+
+	if((paths = malloc(sizeof(char *) * (paths_s + 1))) == NULL){
+		free(path);
+		errno = ENOMEM; /* Cannot allocate memory */
+		return NULL;
+	}
+
+	/* Replace all instances of the path delimiter with 0, and then put the
+	 * next path beginning into paths. */
+	/* This way we can get multiple strings out of one span of memory. */
+	for(*paths = p = path, q = paths + 1; *p != '\0';)
+		if(*p++ == PATH_DELIMITER){
+			*(p - 1) = '\0';
+			*q++ = p;
+		}
+	
+	paths[path_s] = NULL;
+
+	/* Because paths[0] will always be path, we can just free(*paths) at
+	 * the end and discard path */
+	path = NULL;
+
+	return paths;
+}

libshell/libshell.h

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+#include <errno.h>
+#include <stdlib.h> /* getenv(3), malloc(3) */
+#include <string.h> /* memcpy(3) */
+
+/* For the shell variable $PATH */
+#define PATH_NAME "PATH"
+#define PATH_DELIMITER ':'
+
+/* Returns a list of the current paths ordered from first to last priority.
+ * output must be freed and *output must be freed! */
+char **getpaths(void);