sh: On startup of the shell, use PWD from the environment if it is valid.

Unset PWD if it is incorrect and no value for it can be determined.
This preserves the logical current directory across shell invocations.

Example (assuming /home is a symlink):
$ cd
$ pwd
/home/foo
$ sh
$ pwd
/home/foo

Formerly the second pwd would show the physical path (symlinks resolved).

4 files changed, 48 insertions, 10 deletions

diff --git a/bin/sh/cd.c b/bin/sh/cd.c
index 40801ba..aee06e8 100644
--- a/bin/sh/cd.c
+++ b/bin/sh/cd.c
@@ -70,6 +70,7 @@ STATIC int docd(char *, int, int);
 STATIC char *getcomponent(void);
 STATIC char *findcwd(char *);
 STATIC void updatepwd(char *);
+STATIC char *getpwd(void);
 STATIC char *getpwd2(void);
 
 STATIC char *curdir = NULL;	/* current working directory */
@@ -351,7 +352,7 @@ pwdcmd(int argc, char **argv)
 /*
  * Get the current directory and cache the result in curdir.
  */
-char *
+STATIC char *
 getpwd(void)
 {
 	char *p;
@@ -374,7 +375,6 @@ getpwd(void)
 STATIC char *
 getpwd2(void)
 {
-	struct stat stdot, stpwd;
 	char *pwd;
 	int i;
 
@@ -387,12 +387,29 @@ getpwd2(void)
 			break;
 	}
 
-	pwd = getenv("PWD");
+	return NULL;
+}
+
+/*
+ * Initialize PWD in a new shell.
+ * If the shell is interactive, we need to warn if this fails.
+ */
+void
+pwd_init(int warn)
+{
+	char *pwd;
+	struct stat stdot, stpwd;
+
+	pwd = lookupvar("PWD");
 	if (pwd && *pwd == '/' && stat(".", &stdot) != -1 &&
 	    stat(pwd, &stpwd) != -1 &&
 	    stdot.st_dev == stpwd.st_dev &&
 	    stdot.st_ino == stpwd.st_ino) {
-		return pwd;
+		if (curdir)
+			ckfree(curdir);
+		curdir = savestr(pwd);
 	}
-	return NULL;
+	if (getpwd() == NULL && warn)
+		out2fmt_flush("sh: cannot determine working directory\n");
+	setvar("PWD", curdir, VEXPORT);
 }
diff --git a/bin/sh/cd.h b/bin/sh/cd.h
index 0a2d489..f88ce26 100644
--- a/bin/sh/cd.h
+++ b/bin/sh/cd.h
@@ -29,6 +29,6 @@
  * $FreeBSD$
  */
 
-char	*getpwd(void);
+void	 pwd_init(int);
 int	 cdcmd (int, char **);
 int	 pwdcmd(int, char **);
diff --git a/bin/sh/main.c b/bin/sh/main.c
index 50a8813..ecbb12d 100644
--- a/bin/sh/main.c
+++ b/bin/sh/main.c
@@ -153,10 +153,7 @@ main(int argc, char *argv[])
 	init();
 	setstackmark(&smark);
 	procargs(argc, argv);
-	if (getpwd() == NULL && iflag)
-		out2fmt_flush("sh: cannot determine working directory\n");
-	if (getpwd() != NULL)
-		setvar ("PWD", getpwd(), VEXPORT);
+	pwd_init(iflag);
 	if (iflag)
 		chkmail(1);
 	if (argv[0] && argv[0][0] == '-') {
diff --git a/tools/regression/bin/sh/parameters/pwd2.0 b/tools/regression/bin/sh/parameters/pwd2.0
new file mode 100644
index 0000000..29b5531
--- /dev/null
+++ b/tools/regression/bin/sh/parameters/pwd2.0
@@ -0,0 +1,24 @@
+# $FreeBSD$
+# Check that PWD is exported and accepted from the environment.
+set -e
+
+T=$(mktemp -d ${TMPDIR:-/tmp}/sh-test.XXXXXX)
+trap 'rm -rf $T' 0
+cd -P $T
+TP=$(pwd)
+mkdir test1
+ln -s test1 link
+cd link
+[ "$PWD" = "$TP/link" ]
+[ "$(pwd)" = "$TP/link" ]
+[ "$(pwd -P)" = "$TP/test1" ]
+[ "$(sh -c pwd)" = "$TP/link" ]
+[ "$(sh -c pwd\ -P)" = "$TP/test1" ]
+cd ..
+[ "$(pwd)" = "$TP" ]
+cd -P link
+[ "$PWD" = "$TP/test1" ]
+[ "$(pwd)" = "$TP/test1" ]
+[ "$(pwd -P)" = "$TP/test1" ]
+[ "$(sh -c pwd)" = "$TP/test1" ]
+[ "$(sh -c pwd\ -P)" = "$TP/test1" ]