lib: libc: Add initial POSIX getopt() implmain

This commit introduces an initial implementation of the POSIX getopt()
argument parser.

Signed-off-by: Ian Moffett <ian@osmora.org>

2 files changed, 105 insertions, 0 deletions

diff --git a/lib/libc/include/unistd.h b/lib/libc/include/unistd.h
index b9c9f5e..8b03b81 100644
--- a/lib/libc/include/unistd.h
+++ b/lib/libc/include/unistd.h
@@ -60,6 +60,11 @@ off_t lseek(int fildes, off_t offset, int whence);
 pid_t getpid(void);
 pid_t getppid(void);
 
+extern char *optarg;
+extern int optind, opterr, optopt;
+
+int getopt(int argc, char *argv[], const char *optstring);
+
 __END_DECLS
 
 #endif  /* !_UNISTD_H */
diff --git a/lib/libc/src/posix/getopt.c b/lib/libc/src/posix/getopt.c
new file mode 100644
index 0000000..d3cd530
--- /dev/null
+++ b/lib/libc/src/posix/getopt.c
@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2023-2025 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/errno.h>
+#include <unistd.h>
+#include <stdbool.h>
+#include <string.h>
+#include <stdio.h>
+
+char *optarg;
+int optind, opterr, optopt;
+
+int
+getopt(int argc, char *argv[], const char *optstring)
+{
+    size_t optstr_len;
+    char *arg;
+    bool has_arg = false;
+
+    if (argc == 0 || optstring == NULL) {
+        opterr = -EINVAL;
+        return -1;
+    }
+
+    if (optind >= argc) {
+        return -1;
+    }
+
+    arg = argv[optind];
+    optstr_len = strlen(optstring);
+
+    /* Non option argument? */
+    if (arg[0] != '-') {
+        return -1;
+    }
+
+    /*
+     * We will look through each possible flag/option
+     * in the optstring and match it against our arg.
+     */
+    for (size_t i = 0; i < optstr_len; ++i) {
+        if (arg[1] != optstring[i]) {
+            continue;
+        }
+
+        /*
+         * If this option has a ':' right next to it,
+         * it also has an argument.
+         */
+        if (i < optstr_len - 1) {
+            if (optstring[i + 1] == ':') {
+                has_arg = true;
+            }
+        }
+
+        break;
+    }
+
+    /*
+     * Handle cases where the option has an argument
+     * with it (-opt=arg)
+     */
+    if (has_arg && optind < argc ) {
+        if (arg[2] != '=') {
+            opterr = -EINVAL;
+            return -1;
+        }
+        optarg = &arg[3];
+        ++optind;
+    }
+
+    ++optind;
+    return arg[1];
+}