Add the '-e' flag to the 'cd' builtin (#358)

This change adds the -e flag to the cd builtin, as specified in
<https://www.austingroupbugs.net/view.php?id=253>. The -e flag is
used to verify if the the current working directory after 'cd -P'
successfully changes the directory, and returns with exit status 1
if the cwd couldn't be determined. Additionally, it causes all
other errors to return with exit status >1 (i.e., status 2 unless
ENOMEM occurs) if -e and -P are both active.

src/cmd/ksh93/bltins/cd_pwd.c:
- Add -e option to the cd builtin command. It verifies $PWD by
  using test_inode() to execute the equivalent of [[ . -ef $PWD ]].
- The check for restricted mode has been moved after optget to
  allow 'cd -eP' to return with exit status 2 when in restricted
  mode. To avoid changing the previous behavior of cd when -e isn't
  passed, extra checks have been added to prevent cd from printing
  usage information in restricted mode.

src/cmd/ksh93/tests/builtins.sh:
- Add regression tests for the exit status when using the cd -P
  flag with and without -e.

src/cmd/ksh93/data/builtins.c,
src/cmd/ksh93/sh.1:
- Document the addition of -e to the cd builtin.

NEWS

@@ -8,6 +8,12 @@ Any uppercase BUG_* names are modernish shell bug IDs.
 - Fixed an issue on illumos that caused some parameters in the getconf
   builtin to fail.
 
+- The cd built-in command now supports a -e option (as specified in
+  https://www.austingroupbugs.net/view.php?id=253). Passing -e alongside -P
+  is used to guarantee the cd built-in returns with exit status 1 if the
+  current working directory couldn't be determined after successfully changing
+  the directory.
+
 2021-12-01:
 
 - Fixed a memory fault that occurred when a discipline function exited

src/cmd/ksh93/bltins/cd_pwd.c

@@ -20,8 +20,8 @@
 ***********************************************************************/
 #pragma prototyped
 /*
- * cd [-LP]  [dirname]
+ * cd [-L] [-Pe] [dirname]
- * cd [-LP]  [old] [new]
+ * cd [-L] [-Pe] [old] [new]
  * pwd [-LP]
  *
  *   David Korn
@@ -57,29 +57,39 @@ int	b_cd(int argc, char *argv[],Shbltin_t *context)
 	register const char *dp;
 	register Shell_t *shp = context->shp;
 	int saverrno=0;
-	int rval,flag=0;
+	int rval,pflag=0,eflag=0,ret=1;
 	char *oldpwd;
 	Namval_t *opwdnod, *pwdnod;
-	if(sh_isoption(SH_RESTRICTED))
-	{
-		errormsg(SH_DICT,ERROR_exit(1),e_restricted+4);
-		UNREACHABLE();
-	}
 	while((rval = optget(argv,sh_optcd))) switch(rval)
 	{
+		case 'e':
+			eflag = 1;
+			break;
 		case 'L':
-			flag = 0;
+			pflag = 0;
 			break;
 		case 'P':
-			flag = 1;
+			pflag = 1;
 			break;
 		case ':':
+			if(sh_isoption(SH_RESTRICTED))
+				break;
 			errormsg(SH_DICT,2, "%s", opt_info.arg);
 			break;
 		case '?':
+			if(sh_isoption(SH_RESTRICTED))
+				break;
 			errormsg(SH_DICT,ERROR_usage(2), "%s", opt_info.arg);
 			UNREACHABLE();
 	}
+	if(pflag && eflag)
+		ret = 2;  /* exit status is 2 if -eP are both on and chdir failed */
+	if(sh_isoption(SH_RESTRICTED))
+	{
+		/* restricted shells cannot change the directory */
+		errormsg(SH_DICT,ERROR_exit(ret),e_restricted+4);
+		UNREACHABLE();
+	}
 	argv += opt_info.index;
 	argc -= opt_info.index;
 	dir =  argv[0];
@@ -106,7 +116,7 @@ int	b_cd(int argc, char *argv[],Shbltin_t *context)
 		dir = nv_getval(opwdnod);
 	if(!dir || *dir==0)
 	{
-		errormsg(SH_DICT,ERROR_exit(1),argc==2?e_subst+4:e_direct);
+		errormsg(SH_DICT,ERROR_exit(ret),argc==2?e_subst+4:e_direct);
 		UNREACHABLE();
 	}
 	/*
@@ -179,7 +189,7 @@ int	b_cd(int argc, char *argv[],Shbltin_t *context)
 			stakputs(last+PATH_OFFSET);
 			stakputc(0);
 		}
-		if(!flag)
+		if(!pflag)
 		{
 			register char *cp;
 			stakseek(PATH_MAX+PATH_OFFSET);
@@ -200,19 +210,19 @@ int	b_cd(int argc, char *argv[],Shbltin_t *context)
 	{
 		if(saverrno)
 			errno = saverrno;
-		errormsg(SH_DICT,ERROR_system(1),"%s:",dir);
+		errormsg(SH_DICT,ERROR_system(ret),"%s:",dir);
 		UNREACHABLE();
 	}
 success:
 	if(dir == nv_getval(opwdnod) || argc==2)
 		dp = dir;	/* print out directory for cd - */
-	if(flag)
+	if(pflag)
 	{
 		dir = stakptr(PATH_OFFSET);
 		if (!(dir=pathcanon(dir,PATH_PHYSICAL)))
 		{
 			dir = stakptr(PATH_OFFSET);
-			errormsg(SH_DICT,ERROR_system(1),"%s:",dir);
+			errormsg(SH_DICT,ERROR_system(ret),"%s:",dir);
 			UNREACHABLE();
 		}
 		stakseek(dir-stakptr(0));
@@ -223,10 +233,10 @@ success:
 	nv_putval(opwdnod,oldpwd,NV_RDONLY);
 	if(*dir == '/')
 	{
-		flag = strlen(dir);
+		size_t len = strlen(dir);
 		/* delete trailing '/' */
-		while(--flag>0 && dir[flag]=='/')
+		while(--len>0 && dir[len]=='/')
-			dir[flag] = 0;
+			dir[len] = 0;
 		nv_putval(pwdnod,dir,NV_RDONLY);
 		nv_onattr(pwdnod,NV_EXPORT);
 		if(shp->pwd)
@@ -243,13 +253,18 @@ success:
 		path_pwd(shp,0);
 		if(*shp->pwd != '/')
 		{
-			errormsg(SH_DICT,ERROR_system(1),e_direct);
+			errormsg(SH_DICT,ERROR_system(ret),e_direct);
 			UNREACHABLE();
 		}
 	}
 	nv_scan(sh_subtracktree(1),rehash,(void*)0,NV_TAGGED,NV_TAGGED);
 	path_newdir(shp,shp->pathlist);
 	path_newdir(shp,shp->cdpathlist);
+	if(pflag && eflag)
+	{
+		/* Verify the current working directory matches $PWD */
+		return(!test_inode(e_dot,nv_getval(pwdnod)));
+	}
 	return(0);
 }
 

src/cmd/ksh93/data/builtins.c

@@ -441,7 +441,7 @@ const char sh_optbuiltin[] =
 ;
 
 const char sh_optcd[] =
-"[-1c?\n@(#)$Id: cd (ksh 93u+m) 2021-01-19 $\n]"
+"[-1c?\n@(#)$Id: cd (ksh 93u+m) 2021-12-02 $\n]"
 "[--catalog?" SH_DICT "]"
 "[+NAME?cd - change working directory ]"
 "[+DESCRIPTION?\bcd\b changes the current working directory of the "
@@ -482,13 +482,22 @@ const char sh_optcd[] =
 "[P?The present working directory is first converted to an absolute pathname "
 	"that does not contain symbolic link components and symbolic name "
 	"components are expanded in the resulting directory name.]"
+"[e?If the \b-P\b option is in effect and the correct \bPWD\b cannot be "
+	"determined, exit with status 1. All other errors encountered while "
+	"both \b-e\b and \b-P\b are active result in exit status >1 (i.e., "
+	"exit status 2 unless an out of memory error occurred).]"
 "\n"
 "\n[directory]\n"
 "old new\n"
 "\n"
 "[+EXIT STATUS?]{"
-	"[+0?Directory successfully changed.]"
+	"[+0?Directory successfully changed and the \bPWD\b is correct.]"
-	"[+>0?An error occurred.]"
+	"[+0?Directory successfully changed, the \bPWD\b couldn't be obtained "
+	"and a combination of \b-eP\b is not active.]"
+	"[+>0?An error occurred and a combination of \b-eP\b is not active.]"
+	"[+1?Directory successfully changed, the \bPWD\b couldn't be obtained "
+	"and a combination of \b-eP\b is active.]"
+	"[+>1?An error occurred and a combination of \b-eP\b is active.]"
 "}"
 "[+SEE ALSO?\bpwd\b(1), \bgetconf\b(1)]"
 ;

src/cmd/ksh93/sh.1

@@ -5772,9 +5772,9 @@ and invokes this function with an argument of
 .BR 0 .
 .TP
 .PD 0
-\f3cd\fP \*(OK \f3\-LP\fP \*(CK \*(OK \f2arg\^\fP \*(CK
+\f3cd\fP \*(OK \f3\-L\fP \*(CK \*(OK \f3-eP\fP \*(CK \*(OK \f2arg\^\fP \*(CK
 .TP
-\f3cd\fP \*(OK \f3\-LP\fP \*(CK \f2old\^\fP \f2new\^\fP
+\f3cd\fP \*(OK \f3\-L\fP \*(CK \*(OK \f3-eP\fP \*(CK \f2old\^\fP \f2new\^\fP
 .PD
 This command can be in either of two forms.
 In the first form it
@@ -5846,6 +5846,20 @@ or
 on the command line
 determines which method is used.
 .sp .5
+If
+.B \-e
+and
+.B \-P
+are both in effect and the correct
+.BR PWD
+could not be determined after successfully changing the directory,
+.B cd
+will return with exit status one and produce no output.
+If any other error occurs while both flags are active,
+the exit status is greater than one.
+This means the exit status is effectively
+two unless an out of memory error occurs.
+.sp .5
 The
 .B cd\^
 command may not be executed by

src/cmd/ksh93/tests/builtins.sh

@@ -1354,5 +1354,47 @@ if builtin rm 2> /dev/null; then
 	[[ -f $tmp/nonemptydir2/shouldexist || -d $tmp/nonemptydir2 ]] && err_exit 'rm builtin fails to remove all folders and files with -rd options'
 fi
 
+# ======
+# These are regression tests for the cd command's -e and -P flags
+mkdir -p "$tmp/failpwd1"
+cd "$tmp/failpwd1"
+rmdir ../failpwd1
+cd -P .
+got=$?; exp=0
+(( got == exp )) || err_exit "cd -P without -e exits with error status if \$PWD doesn't exist (expected $exp, got $got)"
+cd -eP .
+got=$?; exp=1
+(( got == exp )) || err_exit "cd -eP doesn't fail if \$PWD doesn't exist (expected $exp, got $got)"
+cd "$tmp"
+cd -P "$tmp/notadir" >/dev/null 2>&1
+got=$?; exp=1
+(( got == exp )) || err_exit "cd -P without -e fails with wrong exit status on nonexistent dir (expected $exp, got $got)"
+cd -eP "$tmp/notadir" >/dev/null 2>&1
+got=$?; exp=2
+(( got == exp )) || err_exit "cd -eP fails with wrong exit status on nonexistent dir (expected $exp, got $got)"
+OLDPWD="$tmp/baddir"
+cd -P - >/dev/null 2>&1
+got=$?; exp=1
+(( got == exp )) || err_exit "cd -P without -e fails with wrong exit status on \$OLDPWD (expected $exp, got $got)"
+cd -eP - >/dev/null 2>&1
+got=$?; exp=2
+(( got == exp )) || err_exit "cd -eP fails with wrong exit status on \$OLDPWD (expected $exp, got $got)"
+cd "$tmp" || err_exit "couldn't change directory from nonexistent dir"
+(set -o restricted; cd -P /) >/dev/null 2>&1
+got=$?; exp=1
+(( got == exp )) || err_exit "cd -P in restricted shell has wrong exit status (expected $exp, got $got)"
+(set -o restricted; cd -eP /) >/dev/null 2>&1
+got=$?; exp=2
+(( got == exp )) || err_exit "cd -eP in restricted shell has wrong exit status (expected $exp, got $got)"
+(set -o restricted; cd -?) >/dev/null 2>&1
+got=$?; exp=1
+(( got == exp )) || err_exit "cd -? shows usage info in restricted shell and has wrong exit status (expected $exp, got $got)"
+(cd -P '') >/dev/null 2>&1
+got=$?; exp=1
+(( got == exp )) || err_exit "cd -P to empty string has wrong exit status (expected $exp, got $got)"
+(cd -eP '') >/dev/null 2>&1
+got=$?; exp=2
+(( got == exp )) || err_exit "cd -eP to empty string has wrong exit status (expected $exp, got $got)"
+
 # ======
 exit $((Errors<125?Errors:125))