add new | syntax.

syntax will change.

src/cmd/mk/shell.c

@@ -0,0 +1,76 @@
+#include "mk.h"
+
+static Shell *shells[] = {
+	&shshell,
+	&rcshell
+};
+
+Shell *shellt;
+Word *shellcmd;
+
+typedef struct Shellstack Shellstack;
+struct Shellstack
+{
+	Shell *t;
+	Word *w;
+	Shellstack *next;
+};
+
+Shellstack *shellstack;
+
+char*
+setshell(Word *w)
+{
+	int i;
+
+	if(w->s == nil)
+		return "shell name not found on line";
+
+	for(i=0; i<nelem(shells); i++)
+		if(shells[i]->matchname(w->s))
+			break;
+	if(i == nelem(shells))
+		return "cannot determine shell type";
+	shellt = shells[i];
+	shellcmd = w;
+	return nil;
+}
+
+void
+initshell(void)
+{
+	shellcmd = stow(shells[0]->name);
+	shellt = shells[0];
+}
+
+void
+pushshell(void)
+{
+	Shellstack *s;
+
+	/* save */
+	s = Malloc(sizeof *s);
+	s->t = shellt;
+	s->w = shellcmd;
+	s->next = shellstack;
+	shellstack = s;
+
+	initshell();	/* reset to defaults */
+}
+
+void
+popshell(void)
+{
+	Shellstack *s;
+
+	if(shellstack == nil){
+		fprint(2, "internal shellstack error\n");
+		Exit();
+	}
+
+	s = shellstack;
+	shellstack = s->next;
+	shellt = s->t;
+	shellcmd = s->w;
+	free(s);
+}