Plan 9's rc.

not a clear win over byron's,
but at least it has the right syntax.

src/cmd/rc/fmtquote.c

@@ -0,0 +1,162 @@
+/*
+ * The authors of this software are Rob Pike and Ken Thompson.
+ *              Copyright (c) 2002 by Lucent Technologies.
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose without fee is hereby granted, provided that this entire notice
+ * is included in all copies of any software which is or includes a copy
+ * or modification of this software and in all copies of the supporting
+ * documentation for such software.
+ * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
+ * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHORS NOR LUCENT TECHNOLOGIES MAKE ANY
+ * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
+ * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
+ */
+#include <u.h>
+#include <libc.h>
+#include "fmt.h"
+#include "fmtdef.h"
+
+extern int (*doquote)(int);
+
+/*
+ * How many bytes of output UTF will be produced by quoting (if necessary) this string?
+ * How many runes? How much of the input will be consumed?
+ * The parameter q is filled in by _quotesetup.
+ * The string may be UTF or Runes (s or r).
+ * Return count does not include NUL.
+ * Terminate the scan at the first of:
+ *	NUL in input
+ *	count exceeded in input
+ *	count exceeded on output
+ * *ninp is set to number of input bytes accepted.
+ * nin may be <0 initially, to avoid checking input by count.
+ */
+void
+__quotesetup(char *s, int nin, int nout, Quoteinfo *q, int sharp)
+{
+	int c;
+
+	q->quoted = 0;
+	q->nbytesout = 0;
+	q->nrunesout = 0;
+	q->nbytesin = 0;
+	q->nrunesin = 0;
+	if(sharp || nin==0 || *s=='\0'){
+		if(nout < 2)
+			return;
+		q->quoted = 1;
+		q->nbytesout = 2;
+		q->nrunesout = 2;
+	}
+	for(; nin!=0; nin-=1){
+		c = *s;
+
+		if(c == '\0')
+			break;
+		if(q->nrunesout+1 > nout)
+			break;
+
+		if((c <= L' ') || (c == L'\'') || (doquote!=nil && doquote(c))){
+			if(!q->quoted){
+				if(1+q->nrunesout+1+1 > nout)	/* no room for quotes */
+					break;
+				q->nrunesout += 2;	/* include quotes */
+				q->nbytesout += 2;	/* include quotes */
+				q->quoted = 1;
+			}
+			if(c == '\'')	{
+				q->nbytesout++;
+				q->nrunesout++;	/* quotes reproduce as two characters */
+			}
+		}
+
+		/* advance input */
+		s++;
+		q->nbytesin++;
+		q->nrunesin++;
+
+		/* advance output */
+		q->nbytesout++;
+		q->nrunesout++;
+	}
+}
+
+static int
+qstrfmt(char *sin, Quoteinfo *q, Fmt *f)
+{
+	int r;
+	char *t, *s, *m, *me;
+	ulong fl;
+	int nc, w;
+
+	m = sin;
+	me = m + q->nbytesin;
+
+	w = f->width;
+	fl = f->flags;
+	if(!(fl & FmtLeft) && __fmtpad(f, w - q->nbytesout) < 0)
+		return -1;
+	t = f->to;
+	s = f->stop;
+	FMTCHAR(f, t, s, '\'');
+	for(nc = q->nrunesin; nc > 0; nc--){
+		r = *(uchar*)m++;
+		FMTCHAR(f, t, s, r);
+		if(r == '\'')
+			FMTCHAR(f, t, s, r);
+	}
+
+	FMTCHAR(f, t, s, '\'');
+	f->nfmt += t - (char *)f->to;
+	f->to = t;
+	if(fl & FmtLeft && __fmtpad(f, w - q->nbytesout) < 0)
+		return -1;
+	return 0;
+}
+
+int
+__quotestrfmt(int runesin, Fmt *f)
+{
+	int outlen;
+	char *s;
+	Quoteinfo q;
+
+	f->flags &= ~FmtPrec;	/* ignored for %q %Q, so disable for %s %S in easy case */
+	s = va_arg(f->args, char *);
+	if(!s)
+		return __fmtcpy(f, "<nil>", 5, 5);
+
+	if(f->flush)
+		outlen = 0x7FFFFFFF;	/* if we can flush, no output limit */
+	else
+		outlen = (char*)f->stop - (char*)f->to;
+
+	__quotesetup(s, -1, outlen, &q, f->flags&FmtSharp);
+
+	if(!q.quoted)
+		return __fmtcpy(f, s, q.nrunesin, q.nbytesin);
+	return qstrfmt(s, &q, f);
+}
+
+int
+quotestrfmt(Fmt *f)
+{
+	return __quotestrfmt(0, f);
+}
+
+void
+quotefmtinstall(void)
+{
+	fmtinstall('q', quotestrfmt);
+}
+
+int
+__needsquotes(char *s, int *quotelenp)
+{
+	Quoteinfo q;
+
+	__quotesetup(s, -1, 0x7FFFFFFF, &q, 0);
+	*quotelenp = q.nbytesout;
+
+	return q.quoted;
+}