src/cmd/rc: import rc syntax `delim{cmd} for splitting commands from 9atom

Co-authored-by: <ori@eigenstate.org>

man/man1/rc.1

@@ -228,6 +228,8 @@ The value is a single string containing the components of the named variable
 separated by spaces.  A variable with zero elements yields the empty string.
 .HP
 .BI `{ command }
+.HP
+.BI ` "split " { command }
 .br
 .I rc
 executes the
@@ -240,6 +242,8 @@ If
 .B $ifs
 is not otherwise set, its value is
 .BR "'\ \et\en'" .
+In the second form of the command, split is used instead of
+.BR $ifs .
 .HP
 .BI <{ command }
 .HP

src/cmd/rc/code.c

@@ -94,6 +94,8 @@ outcode(tree *t, int eflag)
 {
 	int p, q;
 	tree *tt;
+	char *ifs;
+
 	if(t==0)
 		return;
 	if(t->type!=NOT && t->type!=';')
@@ -141,14 +143,26 @@ outcode(tree *t, int eflag)
 		emitf(Xconc);
 		break;
 	case '`':
+		emitf(Xmark);
+		if(c0){
+			outcode(c0, 0);
+			emitf(Xglob);
+		}else{
+			if((ifs = strdup("ifs")) == nil)
+				sysfatal("strdup: %r");
+			emitf(Xmark);
+			emitf(Xword);
+			emits(ifs);
+			emitf(Xdol);
+		}
 		emitf(Xbackq);
 		if(havefork){
 			p = emiti(0);
-			outcode(c0, 0);
+			outcode(c1, 0);
 			emitf(Xexit);
 			stuffdot(p);
 		} else
-			emits(fnstr(c0));
+			emits(fnstr(c1));
 		break;
 	case ANDAND:
 		outcode(c0, 0);

src/cmd/rc/exec.c

@@ -218,7 +218,7 @@ main(int argc, char *argv[])
  * Xappend(file)[fd]			open file to append
  * Xassign(name, val)			assign val to name
  * Xasync{... Xexit}			make thread for {}, no wait
- * Xbackq{... Xreturn}			make thread for {}, push stdout
+ * Xbackq(split){... Xreturn}		make thread for {}, push stdout
  * Xbang				complement condition
  * Xcase(pat, value){...}		exec code on match, leave (value) on
  * 					stack

src/cmd/rc/havefork.c

@@ -115,12 +115,14 @@ Xbackq(void)
 	int c, n;
 	char *s, *ewd=&wd[8192], *stop, *q;
 	struct io *f;
-	var *ifs = vlook("ifs");
 	word *v, *nextv;
 	int pfd[2];
 	int pid;
 	Rune r;
-	stop = ifs->val?ifs->val->word:"";
+
+	stop = "";
+	if(runq->argv && runq->argv->words)
+		stop = runq->argv->words->word;
 	if(pipe(pfd)<0){
 		Xerror("can't make pipe");
 		return;
@@ -168,6 +170,7 @@ Xbackq(void)
 		}
 		closeio(f);
 		Waitfor(pid, 0);
+		poplist();	/* ditch split in "stop" */
 		/* v points to reversed arglist -- reverse it onto argv */
 		while(v){
 			nextv = v->next;

src/cmd/rc/parse.c

@@ -409,7 +409,8 @@ yyword(int tok, int *ptok, int eqok)
 	// |	'"' word		{$$=tree1('"', $2);}
 	// |	COUNT word		{$$=tree1(COUNT, $2);}
 	// |	WORD
-	// |	'`' brace		{$$=tree1('`', $2);}
+	// |	'`' brace		{$$=tree2('`', (struct tree*)0, $2);}
+	// |	'`' word brace		{$$=tree2('`', $2, $3);}
 	// |	'(' words ')'		{$$=tree1(PAREN, $2);}
 	// |	REDIR brace		{$$=mung1($1, $2); $$->type=PIPEFD;}
 	// keyword: FOR|IN|WHILE|IF|NOT|TWIDDLE|BANG|SUBSHELL|SWITCH|FN
@@ -499,8 +500,13 @@ word1(int tok, int *ptok)
 		return tree1(COUNT, word1(yylex(), ptok));
 
 	case '`':
-		// |	'`' brace		{$$=tree1('`', $2);}
+		// |	'`' brace		{$$=tree2('`', (struct tree*)0, $2);}
-		t = tree1('`', brace(yylex()));
+		// |	'`' word brace		{$$=tree2('`', $2, $3);}
+		w = nil;
+		tok = dropsp(yylex());
+		if(iswordtok(tok))
+			w = yyword(tok, &tok, 1);
+		t = tree2('`', w, brace(tok));
 		*ptok = yylex();
 		return t;
 

src/cmd/rc/pcmd.c

@@ -32,7 +32,7 @@ pcmd(io *f, tree *t)
 	break;
 	case '^':	pfmt(f, "%t^%t", c0, c1);
 	break;
-	case '`':	pfmt(f, "`%t", c0);
+	case '`':	pfmt(f, "`%t%t", c0, c1);
 	break;
 	case ANDAND:	pfmt(f, "%t && %t", c0, c1);
 	break;

src/cmd/rc/syn.y

@@ -83,7 +83,8 @@ comword: '$' word		{$$=tree1('$', $2);}
 |	'"' word		{$$=tree1('"', $2);}
 |	COUNT word		{$$=tree1(COUNT, $2);}
 |	WORD
-|	'`' brace		{$$=tree1('`', $2);}
+|	'`' brace		{$$=tree2('`', (struct tree*)0, $2);}
+|	'`' word brace		{$$=tree2('`', $2, $3);}
 |	'(' words ')'		{$$=tree1(PAREN, $2);}
 |	REDIRW brace		{$$=mung1($1, $2); $$->type=PIPEFD;}
 keyword: FOR|IN|WHILE|IF|NOT|TWIDDLE|BANG|SUBSHELL|SWITCH|FN