hush: export PWD

function                                             old     new   delta
set_pwd_var                                            -      36     +36
hush_main                                            941     951     +10
evalvar                                             1365    1363      -2
ash_main                                            1364    1362      -2
builtin_cd                                            75      72      -3
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/3 up/down: 46/-7)              Total: 39 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 60 insertions, 5 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 35d5cde58..eca4ab98c 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -12985,7 +12985,7 @@ init(void)
         /* from var.c: */
         {
                 char **envp;
-                char ppid[sizeof(int)*3 + 1];
+                char ppid[sizeof(int)*3 + 2];
                 const char *p;
                 struct stat st1, st2;
 
@@ -12996,7 +12996,7 @@ init(void)
                         }
                 }
 
-                snprintf(ppid, sizeof(ppid), "%u", (unsigned) getppid());
+                sprintf(ppid, "%u", (unsigned) getppid());
                 setvar("PPID", ppid, 0);
 
                 p = lookupvar("PWD");
diff --git a/shell/hush.c b/shell/hush.c
index 7ac29ace2..5794b1ddf 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -58,7 +58,7 @@
  * TODOs:
  *      grep for "TODO" and fix (some of them are easy)
  *      builtins: ulimit
- *      special variables (PWD etc)
+ *      special variables (done: PWD)
  *      follow IFS rules more precisely, including update semantics
  *      export builtin should be special, its arguments are assignments
  *          and therefore expansion of them should be "one-word" expansion:
@@ -1432,6 +1432,13 @@ static int set_local_var(char *str, int flg_export, int local_lvl, int flg_read_
         return 0;
 }
 
+/* Used at startup and after each cd */
+static void set_pwd_var(int exp)
+{
+        set_local_var(xasprintf("PWD=%s", get_cwd(/*force:*/ 1)),
+                /*exp:*/ exp, /*lvl:*/ 0, /*ro:*/ 0);
+}
+
 static int unset_local_var_len(const char *name, int name_len)
 {
         struct variable *cur;
@@ -1604,6 +1611,9 @@ static const char* setup_prompt_string(int promptmode)
                 /* Set up the prompt */
                 if (promptmode == 0) { /* PS1 */
                         free((char*)G.PS1);
+                        /* bash uses $PWD value, even if it is set by user.
+                         * It uses current dir only if PWD is unset.
+                         * We always use current dir. */
                         G.PS1 = xasprintf("%s %c ", get_cwd(0), (geteuid() != 0) ? '$' : '#');
                         prompt_str = G.PS1;
                 } else
@@ -6432,8 +6442,49 @@ int hush_main(int argc, char **argv)
                 }
                 e++;
         }
+        /* reinstate HUSH_VERSION */
         debug_printf_env("putenv '%s'\n", hush_version_str);
-        putenv((char *)hush_version_str); /* reinstate HUSH_VERSION */
+        putenv((char *)hush_version_str);
+
+        /* Export PWD */
+        set_pwd_var(/*exp:*/ 1);
+        /* bash also exports SHLVL and _,
+         * and sets (but doesn't export) the following variables:
+         * BASH=/bin/bash
+         * BASH_VERSINFO=([0]="3" [1]="2" [2]="0" [3]="1" [4]="release" [5]="i386-pc-linux-gnu")
+         * BASH_VERSION='3.2.0(1)-release'
+         * HOSTTYPE=i386
+         * MACHTYPE=i386-pc-linux-gnu
+         * OSTYPE=linux-gnu
+         * HOSTNAME=<xxxxxxxxxx>
+         * PPID=<NNNNN>
+         * EUID=<NNNNN>
+         * UID=<NNNNN>
+         * GROUPS=()
+         * LINES=<NNN>
+         * COLUMNS=<NNN>
+         * BASH_ARGC=()
+         * BASH_ARGV=()
+         * BASH_LINENO=()
+         * BASH_SOURCE=()
+         * DIRSTACK=()
+         * PIPESTATUS=([0]="0")
+         * HISTFILE=/<xxx>/.bash_history
+         * HISTFILESIZE=500
+         * HISTSIZE=500
+         * MAILCHECK=60
+         * PATH=/usr/gnu/bin:/usr/local/bin:/bin:/usr/bin:.
+         * SHELL=/bin/bash
+         * SHELLOPTS=braceexpand:emacs:hashall:histexpand:history:interactive-comments:monitor
+         * TERM=dumb
+         * OPTERR=1
+         * OPTIND=1
+         * IFS=$' \t\n'
+         * PS1='\s-\v\$ '
+         * PS2='> '
+         * PS4='+ '
+         */
+
 #if ENABLE_FEATURE_EDITING
         G.line_input_state = new_line_input_t(FOR_SHELL);
 #endif
@@ -6816,7 +6867,11 @@ static int FAST_FUNC builtin_cd(char **argv)
                 bb_perror_msg("cd: %s", newdir);
                 return EXIT_FAILURE;
         }
-        get_cwd(1);
+        /* Read current dir (get_cwd(1) is inside) and set PWD.
+         * Note: do not enforce exporting. If PWD was unset or unexported,
+         * set it again, but do not export. bash does the same.
+         */
+        set_pwd_var(/*exp:*/ 0);
         return EXIT_SUCCESS;
 }