[RFC PATCH] RFC: expand_tilde () for potential future path expansion
Tomi Ollila
tomi.ollila at iki.fi
Sat May 14 04:33:08 PDT 2016
One implementation how to do this. Output of the "tests".
$ sh expand-tilde.c
+ exec gcc -std=c99 -Wall -Wstrict-prototypes -Winit-self -Wformat=2 -Wcast-align -Wpointer-arith -Wextra -Wwrite-strings -Wcast-qual -Wshadow -Wmissing-include-dirs -Wundef -Wbad-function-cast -Wlogical-op -Waggregate-return -Wold-style-definition -Wmissing-prototypes -Wmissing-declarations -Wredundant-decls -Wnested-externs -Winline -Wvla -Woverlength-strings -Wpadded -O2 -o expand-tilde expand-tilde.c
$
$ ./expand-tilde
input '~', expanded '/home/too', rest ''
input '~root', expanded '/root', rest ''
$ HOME=/a/b/c/ ./expand-tilde '~' '~'/ "~$USER" "~$USER/" '~'root '~'root/ '~none' '~none/'
input '~', expanded '/a/b/c/', rest ''
input '~/', expanded '/a/b/c/', rest '/'
input '~too', expanded '/home/too', rest ''
input '~too/', expanded '/home/too', rest '/'
input '~root', expanded '/root', rest ''
input '~root/', expanded '/root', rest '/'
input '~none', expanded '(null)', rest '~none'
input '~none/', expanded '(null)', rest '~none/'
$ HOME= ./expand-tilde '~' '~'/ "~$USER" "~$USER/"
input '~', expanded '', rest ''
input '~/', expanded '', rest '/'
input '~too', expanded '/home/too', rest ''
input '~too/', expanded '/home/too', rest '/'
$ ( unset HOME; ./expand-tilde '~' '~'/ "~$USER" "~$USER/" )
input '~', expanded '(null)', rest '~'
input '~/', expanded '(null)', rest '~/'
input '~too', expanded '/home/too', rest ''
input '~too/', expanded '/home/too', rest '/'
---
util/expand-tilde.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 102 insertions(+)
create mode 100644 util/expand-tilde.c
diff --git a/util/expand-tilde.c b/util/expand-tilde.c
new file mode 100644
index 0000000..e3097e6
--- /dev/null
+++ b/util/expand-tilde.c
@@ -0,0 +1,102 @@
+#if 0 /* -*- mode: c; c-file-style: "stroustrup"; tab-width: 8; -*-
+ set -eu; trg=`exec basename "$0" .c`; rm -f "$trg"
+ WARN="-Wall -Wstrict-prototypes -Winit-self -Wformat=2" # -pedantic
+ WARN="$WARN -Wcast-align -Wpointer-arith " # -Wfloat-equal #-Werror
+ WARN="$WARN -Wextra -Wwrite-strings -Wcast-qual -Wshadow" # -Wconversion
+ WARN="$WARN -Wmissing-include-dirs -Wundef -Wbad-function-cast -Wlogical-op"
+ WARN="$WARN -Waggregate-return -Wold-style-definition"
+ WARN="$WARN -Wmissing-prototypes -Wmissing-declarations -Wredundant-decls"
+ WARN="$WARN -Wnested-externs -Winline -Wvla -Woverlength-strings -Wpadded"
+ case ${1-} in '') set x -O2; shift; esac
+ #case ${1-} in '') set x -ggdb; shift; esac
+ set -x; exec ${CC:-gcc} -std=c99 $WARN "$@" -o "$trg" "$0"
+ exit $?
+ */
+#endif
+/*
+ * $ expand-tilde.c $
+ *
+ * Author: Tomi Ollila -- too ät iki piste fi
+ *
+ * Created: Sat 14 May 2016 13:10:35 EEST too
+ * Last modified: Sat 14 May 2016 14:22:10 +0300 too
+ *
+ * *** Public Domain ***
+ */
+
+#include <stdlib.h>
+#include <sys/types.h>
+#include <pwd.h>
+
+/* USER_NAME_MAX_LENGTH is not usually defined (publicly in standard paths). */
+
+#ifndef USER_NAME_MAX_LENGTH
+#define USER_NAME_MAX_LENGTH 32
+#endif
+
+static // for -Wmissing-prototypes
+/* This is modeled after expand-file-name in emacs sources (fileio.c);
+ * simplified and using constant buffer for user name.
+ * neither emacs nor this implementation has restrictions in username chars
+ * ...we may be looking forward for multibyte usernames...
+ */
+const char * expand_tilde(const char * path, const char ** rest)
+{
+ if (path == NULL || path[0] != '~') {
+ *rest = path;
+ return NULL;
+ }
+
+ if (path[1] == '/' || path[1] == '\0') {
+ const char * home = getenv ("HOME");
+ *rest = home? path + 1: path;
+ return home;
+ }
+
+ char username[USER_NAME_MAX_LENGTH + 1];
+ int namepos = 0;
+ const char * pathp = path + 1;
+
+ while (1) {
+ username[namepos++] = pathp++[0];
+ if (pathp[0] == '/' || pathp[0] == '\0')
+ break;
+ if (namepos >= USER_NAME_MAX_LENGTH) {
+ *rest = path;
+ return NULL;
+ }
+ }
+ username[namepos] = '\0';
+
+ struct passwd * pw = getpwnam (username);
+ if (pw == NULL) {
+ *rest = path;
+ return NULL;
+ }
+ *rest = path + 1 + namepos;
+ return pw->pw_dir;
+ }
+
+#include <stdio.h>
+
+static void print_expanded(const char * path)
+{
+ const char * rest;
+ const char * expanded = expand_tilde(path, &rest);
+ printf("input '%s', expanded '%s', rest '%s'\n",
+ path, expanded, rest);
+}
+
+int main(int argc, char * argv[])
+{
+ printf("\n");
+ if (argc < 2) {
+ print_expanded("~\0-- this something not to be seen in output --");
+ print_expanded("~root\0-- this something not to be seen in output --");
+ } else {
+ for (int i = 1; i < argc; i++)
+ print_expanded(argv[i]);
+ }
+ printf("\n");
+ return 0;
+}
--
2.8.2
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