From 4da12aae651dac2f0c6818f54d5d8b5f0a9e8bf6 Mon Sep 17 00:00:00 2001
From: Drew DeVault <sir@cmpwn.com>
Date: Sat, 29 Sep 2018 16:28:53 -0400
Subject: [PATCH] Implement 'shift' builtin

---
 builtin/builtin.c |  1 +
 builtin/shift.c   | 49 +++++++++++++++++++++++++++++++++++++++++++++++
 include/builtin.h |  1 +
 meson.build       |  1 +
 4 files changed, 52 insertions(+)
 create mode 100644 builtin/shift.c

diff --git a/builtin/builtin.c b/builtin/builtin.c
index 4e9a07c..bb42ca9 100644
--- a/builtin/builtin.c
+++ b/builtin/builtin.c
@@ -22,6 +22,7 @@ static const struct builtin builtins[] = {
 	{ "exit", builtin_exit, true },
 	{ "false", builtin_false, false },
 	{ "set", builtin_set, true },
+	{ "shift", builtin_shift, true },
 	{ "times", builtin_times, true },
 	{ "true", builtin_true, false },
 };
diff --git a/builtin/shift.c b/builtin/shift.c
new file mode 100644
index 0000000..0289813
--- /dev/null
+++ b/builtin/shift.c
@@ -0,0 +1,49 @@
+#include <mrsh/builtin.h>
+#include <mrsh/shell.h>
+#include <stdlib.h>
+#include "builtin.h"
+
+static const char shift_usage[] = "usage: shift [n]\n";
+
+int builtin_shift(struct mrsh_state *state, int argc, char *argv[]) {
+	if (argc > 2) {
+		fprintf(stderr, shift_usage);
+		return EXIT_FAILURE;
+	}
+	int n = 1;
+	if (argc == 2) {
+		char *endptr;
+		n = strtol(argv[1], &endptr, 10);
+		if (*endptr != '\0') {
+			fprintf(stderr, shift_usage);
+			if (!state->interactive) {
+				state->exit = EXIT_FAILURE;
+			}
+			return EXIT_FAILURE;
+		}
+	}
+	if (n == 0) {
+		return EXIT_SUCCESS;
+	} else if (n < 1) {
+		fprintf(stderr, "shift: [n] must be positive\n");
+		if (!state->interactive) {
+			state->exit = EXIT_FAILURE;
+		}
+		return EXIT_FAILURE;
+	} else if (n > state->argc - 1) {
+		fprintf(stderr, "shift: [n] must be less than $#\n");
+		if (!state->interactive) {
+			state->exit = EXIT_FAILURE;
+		}
+		return EXIT_FAILURE;
+	}
+	for (int i = 1, j = n + 1; j < state->argc; ++i, ++j) {
+		if (j <= state->argc - n) {
+			state->argv[i] = state->argv[j];
+		} else {
+			free(state->argv[i]);
+		}
+	}
+	state->argc -= n;
+	return EXIT_SUCCESS;
+}
diff --git a/include/builtin.h b/include/builtin.h
index 8ca90e4..07925e7 100644
--- a/include/builtin.h
+++ b/include/builtin.h
@@ -13,6 +13,7 @@ int builtin_cd(struct mrsh_state *state, int argc, char *argv[]);
 int builtin_colon(struct mrsh_state *state, int argc, char *argv[]);
 int builtin_exit(struct mrsh_state *state, int argc, char *argv[]);
 int builtin_eval(struct mrsh_state *state, int argc, char *argv[]);
+int builtin_shift(struct mrsh_state *state, int argc, char *argv[]);
 int builtin_source(struct mrsh_state *state, int argc, char *argv[]);
 int builtin_times(struct mrsh_state *state, int argc, char *argv[]);
 int builtin_set(struct mrsh_state *state, int argc, char *argv[]);
diff --git a/meson.build b/meson.build
index 45d2c42..d0a665c 100644
--- a/meson.build
+++ b/meson.build
@@ -39,6 +39,7 @@ lib_mrsh = library(
 		'builtin/eval.c',
 		'builtin/exit.c',
 		'builtin/set.c',
+		'builtin/shift.c',
 		'builtin/source.c',
 		'builtin/times.c',
 		'builtin/true.c',
-- 
2.38.5