Userland: Add a man command

Author: https://github.com/bugaevc
Commit: https://github.com/SerenityOS/serenity/commit/36eea6c04bb
Pull-request: https://github.com/SerenityOS/serenity/pull/609
Reviewed-by: https://github.com/awesomekling ✅

Userland/man.cpp

@@ -0,0 +1,70 @@
+#include <AK/String.h>
+#include <LibCore/CFile.h>
+#include <LibMarkdown/MDDocument.h>
+#include <stdio.h>
+#include <unistd.h>
+
+int main(int argc, char* argv[])
+{
+    String name;
+    String section;
+
+    if (argc < 2 || argc > 3) {
+        fprintf(stderr, "Usage:\t%s <name>\n\t%s <section <name>\n", argv[0], argv[0]);
+        exit(1);
+    }
+
+    if (argc == 2) {
+        name = argv[1];
+    } else {
+        section = argv[1];
+        name = argv[2];
+    }
+
+    auto make_path = [&](String s) {
+        return String::format("/usr/share/man/man%s/%s.md", s.characters(), name.characters());
+    };
+    if (section.is_null()) {
+        String sections[] = {
+            "1",
+            "2",
+            "3",
+            "4",
+            "5",
+            "6",
+            "7",
+            "8"
+        };
+        for (auto& s : sections) {
+            String path = make_path(s);
+            if (access(path.characters(), R_OK) == 0) {
+                section = s;
+                break;
+            }
+        }
+        if (section.is_null()) {
+            fprintf(stderr, "No man page for %s\n", name.characters());
+            exit(1);
+        }
+    }
+
+    auto file = CFile::construct();
+    file->set_filename(make_path(section));
+
+    if (!file->open(CIODevice::OpenMode::ReadOnly)) {
+        perror("Failed to open man page file");
+        exit(1);
+    }
+    dbg() << "Loading man page from " << file->filename();
+    auto buffer = file->read_all();
+    String source { (char*)buffer.data(), buffer.size() };
+
+    printf("%s(%s)\t\tSerenity manual\n", name.characters(), section.characters());
+
+    MDDocument document;
+    bool success = document.parse(source);
+    ASSERT(success);
+
+    String rendered = document.render_for_terminal();
+    printf("%s", rendered.characters());
+}