chmod: partial implementation of the chmod command

Makefile

@@ -21,6 +21,8 @@ all:
 	@make -C head
 	@echo "\x1B[0;1;35m make\x1B[0m utilities/reset"
 	@make -C reset
+	@echo "\x1B[0;1;35m make\x1B[0m utilities/chmod"
+	@make -C chmod
 
 install:
 	@mkdir -p out
@@ -46,6 +48,8 @@ install:
 	@make install -C head
 	@echo "\x1B[0;1;35m make\x1B[0m install utilities/reset"
 	@make install -C reset
+	@echo "\x1B[0;1;35m make\x1B[0m install utilities/chmod"
+	@make install -C chmod
 
 clean:
 	@echo "\x1B[0;1;35m make\x1B[0m clean utilities/hello"
@@ -69,4 +73,6 @@ clean:
 	@echo "\x1B[0;1;35m make\x1B[0m clean utilities/head"
 	@make clean -C head
 	@echo "\x1B[0;1;35m make\x1B[0m clean utilities/reset"
-	@make clean -C reset
+	@make clean -C reset
+	@echo "\x1B[0;1;35m make\x1B[0m clean utilities/chmod"
+	@make clean -C chmod

chmod/Makefile

@@ -0,0 +1,23 @@
+PLATFORM=x86_64-lux
+CCFLAGS=-Wall -c -O3
+LDFLAGS=-llux
+CC=x86_64-lux-gcc
+LD=x86_64-lux-gcc
+SRC:=$(shell find . -type f -name "*.c")
+OBJ:=$(SRC:.c=.o)
+
+all: chmod
+
+%.o: %.c
+	@echo "\x1B[0;1;32m cc  \x1B[0m $<"
+	@$(CC) $(CCFLAGS) -o $@ $<
+
+chmod: $(OBJ)
+	@echo "\x1B[0;1;93m ld  \x1B[0m chmod"
+	@$(LD) $(OBJ) -o chmod $(LDFLAGS)
+
+install: chmod
+	@cp chmod ../out/
+
+clean:
+	@rm -f chmod $(OBJ)

chmod/chmod.c

@@ -0,0 +1,97 @@
+/*
+ * luxOS - a unix-like operating system
+ * Omar Elghoul, 2024
+ * 
+ * chmod: Implementation of the chmod command
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/stat.h>
+
+static const mode_t bitmap[] = {
+    S_IXOTH,
+    S_IWOTH,
+    S_IROTH,
+    S_IXGRP,
+    S_IWGRP,
+    S_IRGRP,
+    S_IXUSR,
+    S_IWUSR,
+    S_IRUSR
+};
+
+int parse(const char *modestr, mode_t *set, mode_t *clear) {
+    *set = 0;
+    *clear = 0;
+
+    /* numerical mode setting */
+    if(modestr[0] >= '0' && modestr[0] <= '9') {
+        int num = atoi(modestr);
+
+        for(int i = 0; i < 3; i++) {
+            int digit = num % 10;
+            num /= 10;
+            if(digit > 7) return 1;
+
+            if(digit & 1) {     // execute
+                *set |= bitmap[i * 3];
+            } else {
+                *clear |= bitmap[i * 3];
+            }
+
+            if(digit & 2) {     // write
+                *set |= bitmap[(i * 3) + 1];
+            } else {
+                *clear |= bitmap[(i * 3) + 1];
+            }
+
+            if(digit & 4) {     // read
+                *set |= bitmap[(i * 3) + 2];
+            } else {
+                *clear |= bitmap[(i * 3) + 2];
+            }
+        }
+
+        return 0;
+    }
+
+    /* TODO: symbolic mode setting */
+    return 1;
+}
+
+int main(int argc, char **argv) {
+    /* TODO: add support for -R to recursively change file modes */
+
+    if(argc < 3) {
+        fprintf(stderr, "usage: %s [-R] mode file...\n", argv[0]);
+        return EXIT_FAILURE;
+    }
+
+    mode_t set = 0, clear = 0;
+    if(parse(argv[1], &set, &clear)) {
+        fprintf(stderr, "%s: invalid mode -- %s\n", argv[0], argv[1]);
+        return EXIT_FAILURE;
+    }
+
+    int errors = 0;
+
+    struct stat st;
+    for(int i = 2; i < argc; i++) {
+        if(stat(argv[i], &st)) {
+            perror(argv[i]);
+            errors++;
+            continue;
+        }
+
+        st.st_mode &= ~clear;
+        st.st_mode |= set;
+        if(chmod(argv[i], st.st_mode)) {
+            perror(argv[i]);
+            errors++;
+        }
+    }
+
+    return errors;
+}