implement support for parameter substitution via #/% operators

1 files changed, 22 insertions, 0 deletions

diff --git a/shell/match.h b/shell/match.h
new file mode 100644
index 000000000..863f52539
--- /dev/null
+++ b/shell/match.h
@@ -0,0 +1,22 @@
+/* match.h - interface to shell ##/%% matching code */
+
+typedef char *(*scan_t)(char *string, char *match, bool zero);
+
+char *scanleft(char *string, char *match, bool zero);
+char *scanright(char *string, char *match, bool zero);
+
+static inline scan_t pick_scan(char op1, char op2, bool *zero)
+{
+	/* #  - scanleft
+	 * ## - scanright
+	 * %  - scanright
+	 * %% - scanleft
+	 */
+	if (op1 == '#') {
+		*zero = true;
+		return op1 == op2 ? scanright : scanleft;
+	} else {
+		*zero = false;
+		return op1 == op2 ? scanleft : scanright;
+	}
+}