4 files changed, 52 insertions(+), 0 deletions(-)

M builtin/builtin.c
A builtin/shift.c
M include/builtin.h
M meson.build

@@ 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 },
 };

@@ 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;
+}

@@ 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[]);

@@ 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',