sh: Add $'quoting' (C-style escape sequences).

A string between $' and ' may contain backslash escape sequences similar to
the ones in a C string constant (except that a single-quote must be escaped
and a double-quote need not be). Details are in the sh(1) man page.

This construct is useful to include unprintable characters, tabs and
newlines in strings; while this can be done with a command substitution
containing a printf command, that needs ugly workarounds if the result is to
end with a newline as command substitution removes all trailing newlines.

The construct may also be useful in future to describe unprintable
characters without needing to write those characters themselves in 'set -x',
'export -p' and the like.

The implementation attempts to comply to the proposal for the next issue of
the POSIX specification. Because this construct is not in POSIX.1-2008,
using it in scripts intended to be portable is unwise.

Matching the minimal locale support in the rest of sh, the \u and \U
sequences are currently not useful.

Exp-run done by: pav (with some other sh(1) changes)

1 files changed, 2 insertions, 0 deletions

diff --git a/bin/sh/mksyntax.c b/bin/sh/mksyntax.c
index 6bd1390..9aa7450 100644
--- a/bin/sh/mksyntax.c
+++ b/bin/sh/mksyntax.c
@@ -64,6 +64,7 @@ struct synclass synclass[] = {
 	{ "CWORD",	"character is nothing special" },
 	{ "CNL",	"newline character" },
 	{ "CBACK",	"a backslash character" },
+	{ "CSBACK",	"a backslash character in single quotes" },
 	{ "CSQUOTE",	"single quote" },
 	{ "CDQUOTE",	"double quote" },
 	{ "CENDQUOTE",	"a terminating quote" },
@@ -224,6 +225,7 @@ main(int argc __unused, char **argv __unused)
 	init();
 	fputs("\n/* syntax table used when in single quotes */\n", cfile);
 	add("\n", "CNL");
+	add("\\", "CSBACK");
 	add("'", "CENDQUOTE");
 	/* ':/' for tilde expansion, '-' for [a\-x] pattern ranges */
 	add("!*?[=~:/-", "CCTL");