Add support for dynamic file descriptors to the MirBSD Korn Shell.

mksh-dynamicfd.patch

Index: check.t
===================================================================
RCS file: /cvs/src/bin/mksh/check.t,v
retrieving revision 1.732
diff -u -r1.732 check.t
--- check.t	17 May 2016 15:36:56 -0000	1.732
+++ check.t	27 May 2016 01:47:35 -0000
@@ -10032,6 +10032,28 @@
 	bar
 	baz
 ---
+name: mkshiop-3
+description:
+	Check support of dynamic file descriptors
+category: !convfds
+stdin:
+	exec 9<&- 10<&- 11<&- 12<&-
+	exec {FDA}<<< foo
+	read -u$FDA bar
+	echo x$bar$FDA
+	exec {FDB}<<< baz
+	read -u$FDB bar
+	echo x$bar$FDB
+	exec {FDA}<&-
+	exec {FDB}<&-
+	exec {FDC}<<< frob
+	read -u$FDC bar
+	echo x$bar$FDC
+expected-stdout:
+	xfoo10
+	xbaz11
+	xfrob10
+---
 name: oksh-eval
 description:
 	Check expansions.
Index: exec.c
===================================================================
RCS file: /cvs/src/bin/mksh/exec.c,v
retrieving revision 1.173
diff -u -r1.173 exec.c
--- exec.c	9 Apr 2016 16:41:32 -0000	1.173
+++ exec.c	27 May 2016 01:47:35 -0000
@@ -1363,6 +1363,7 @@
 	int u = -1;
 	char *cp = iop->ioname;
 	int iotype = iop->ioflag & IOTYPE;
+	struct tbl *vp = NULL;
 	bool do_open = true, do_close = false, do_fstat = false;
 	int flags = 0;
 	struct ioword iotmp;
@@ -1371,6 +1372,9 @@
 	if (iotype != IOHERE)
 		cp = evalonestr(cp, DOTILDE|(Flag(FTALKING_I) ? DOGLOB : 0));

+	if (iop->ioflag & IODYNAMIC)
+		vp = global(evalstr(iop->varname, 0));
+
 	/* Used for tracing and error messages to print expanded cp */
 	iotmp = *iop;
 	iotmp.ioname = (iotype == IOHERE) ? NULL : cp;
@@ -1434,6 +1438,12 @@
 			/* prevent error return below */
 			u = 1009;
 			do_close = true;
+			/* read variable for {FD}>&- syntax */
+			if (iop->ioflag & IODYNAMIC) {
+				int i = 0;
+				getn(str_val(vp), &i);
+				iop->unit = i;
+			}
 		} else if ((u = check_fd(cp,
 		    X_OK | ((iop->ioflag & IORDUP) ? R_OK : W_OK),
 		    &emsg)) < 0) {
@@ -1444,7 +1454,7 @@
 			afree(sp, ATEMP);
 			return (-1);
 		}
-		if (u == (int)iop->unit)
+		if (u == (int)iop->unit && !(iop->ioflag & IODYNAMIC))
 			/* "dup from" == "dup to" */
 			return (0);
 		break;
@@ -1478,6 +1488,21 @@
 		}
 		return (-1);
 	}
+	/* If unit was dynamic, pick an unused unit (fd) and store in variable */
+	if (iop->ioflag & IODYNAMIC && !do_close) {
+		/* Dynamic file descriptors should always be >=10 */
+		if (u < 10) {
+			int nu;
+			nu = fcntl(u, F_DUPFD, 10);
+			if (nu >= 0) {
+				if (iotype != IODUP)
+					close(u);
+				u = nu;
+			}
+		}
+		iop->unit = u;
+		setint(vp, iop->unit);
+	}
 	/* Do not save if it has already been redirected (i.e. "cat >x >y"). */
 	if (e->savefd[iop->unit] == 0) {
 		/* If these are the same, it means unit was previously closed */
Index: lex.c
===================================================================
RCS file: /cvs/src/bin/mksh/lex.c,v
retrieving revision 1.224
diff -u -r1.224 lex.c
--- lex.c	5 May 2016 22:46:23 -0000	1.224
+++ lex.c	27 May 2016 01:47:35 -0000
@@ -890,8 +890,18 @@
 	    c == '<' || c == '>')) {
 		struct ioword *iop = alloc(sizeof(struct ioword), ATEMP);

+		iop->ioflag = 0;
+
 		if (Xlength(ws, wp) == 0)
 			iop->unit = c == '<' ? 0 : 1;
+		else if (dp[0] == CHAR && dp[1] == '{' &&
+		    dp[Xlength(ws, wp) - 2] == CHAR && dp[Xlength(ws, wp) - 1] == '}' &&
+		    Xlength(ws, wp) > 4) {
+			iop->ioflag |= IODYNAMIC;
+			iop->varname = alloc(Xlength(ws, wp) - 4 + 1, ATEMP);
+			memcpy(iop->varname, dp + 2, Xlength(ws, wp) - 4);
+			iop->varname[Xlength(ws, wp) - 4] = '\0';
+		}
 		else for (iop->unit = 0, c2 = 0; c2 < Xlength(ws, wp); c2 += 2) {
 			if (dp[c2] != CHAR)
 				goto no_iop;
@@ -908,16 +918,15 @@
 				goto no_iop;
 			}
 			c = c2;
-			iop->ioflag = IOBASH;
-		} else
-			iop->ioflag = 0;
+			iop->ioflag |= IOBASH;
+		}

 		c2 = getsc();
 		/* <<, >>, <> are ok, >< is not */
 		if (c == c2 || (c == '<' && c2 == '>')) {
 			iop->ioflag |= c == c2 ?
 			    (c == '>' ? IOCAT : IOHERE) : IORDWR;
-			if (iop->ioflag == IOHERE) {
+			if (iop->ioflag & IOHERE) {
 				if ((c2 = getsc()) == '-')
 					iop->ioflag |= IOSKIP;
 				else if (c2 == '<')
Index: sh.h
===================================================================
RCS file: /cvs/src/bin/mksh/sh.h,v
retrieving revision 1.772
diff -u -r1.772 sh.h
--- sh.h	17 May 2016 15:36:59 -0000	1.772
+++ sh.h	27 May 2016 01:47:35 -0000
@@ -1429,6 +1429,7 @@
 	char *heredoc;		/* content of heredoc */
 	unsigned short ioflag;	/* action (below) */
 	short unit;		/* unit (fd) affected */
+    char *varname;		/* variable in which to store unit */
 };

 /* ioword.flag - type of redirection */
@@ -1447,6 +1448,7 @@
 #define IOBASH		BIT(9)	/* &> etc. */
 #define IOHERESTR	BIT(10)	/* <<< (here string) */
 #define IONDELIM	BIT(11)	/* null delimiter (<<) */
+#define IODYNAMIC	BIT(12)	/* dynamic fd allocation ({}<) */

 /* execute/exchild flags */
 #define XEXEC	BIT(0)		/* execute without forking */

This adds the functionality described here: http://www.unix.com/302586545-post4.html

This was already available in recent versions of the Bash, KSH, and ZSH shells.

One of the more interesting uses for this is in conjunction with the automatic creation of unlinked temp-files when you use a here-doc/string:

exec {FD}<<<''
echo "Hello, temp!" >/dev/fd/$FD
cat </dev/fd/$FD
exec {FD}<&-

Or, even access the tempfile via /proc/$$/fd/$FD like this:

exec {KEY_FD}<<'END_KEY'
-----BEGIN RSA PRIVATE KEY-----
... key embedded in script here ...
-----END RSA PRIVATE KEY-----
END_KEY
ssh -T user@remotehost -i /proc/$$/fd/${KEY_FD} <<'END_SCRIPT'
echo "Hello from `hostname`"
END_SCRIPT

Of course both of these examples could be written without dynamic file descriptors entirely, but making the descriptors dynamic allows interoperability with other script-libraries and functions that might use conflicting file descriptors.