File: parse_filename function which handle ~ and environment variable in filenames

src/file.cc

@@ -13,6 +13,40 @@
 namespace Kakoune
 {
 
+bool isidentifier(char c)
+{
+    return std::isalnum(c) or c == '_';
+}
+
+std::string parse_filename(const std::string& filename)
+{
+    if (filename.length() > 2 and filename[0] == '~' and filename[1] == '/')
+        return parse_filename("$HOME/" + filename.substr(2));
+
+    size_t pos = 0;
+    std::string result;
+    for (size_t i = 0; i < filename.length(); ++i)
+    {
+        if (filename[i] == '$' and (i == 0 or filename[i-1] != '\\'))
+        {
+            result += filename.substr(pos, i - pos);
+            size_t end = i+1;
+            while (end != filename.length() and isidentifier(filename[end]))
+                ++end;
+            std::string var_name = filename.substr(i+1, end - i - 1);
+            const char* var_value = getenv(var_name.c_str());
+            if (var_value)
+                result += var_value;
+
+            pos = end;
+        }
+    }
+    if (pos != filename.length())
+        result += filename.substr(pos);
+
+    return result;
+}
+
 std::string read_file(const std::string& filename)
 {
    int fd = open(filename.c_str(), O_RDONLY);

src/file.hh

@@ -23,6 +23,10 @@ struct file_not_found : file_access_error
 };
 
 class Buffer;
+
+// parse ~/ and $env values in filename and returns the translated filename
+std::string parse_filename(const std::string& filename);
+
 std::string read_file(const std::string& filename);
 Buffer* create_buffer_from_file(const std::string& filename);
 void write_buffer_to_file(const Buffer& buffer, const std::string& filename);

src/main.cc

@@ -535,7 +535,8 @@ void write_buffer(const CommandParameters& params, const Context& context)
         throw wrong_argument_count();
 
     Buffer& buffer = context.window().buffer();
-    std::string filename = params.empty() ? buffer.name() : params[0];
+    std::string filename = params.empty() ? buffer.name()
+                                          : parse_filename(params[0]);
 
     write_buffer_to_file(buffer, filename);
     buffer.notify_saved();
@@ -695,7 +696,7 @@ void exec_commands_in_file(const CommandParameters& params,
     if (params.size() != 1)
         throw wrong_argument_count();
 
-    std::string file_content = read_file(params[0]);
+    std::string file_content = read_file(parse_filename(params[0]));
     CommandManager& cmd_manager = CommandManager::instance();
 
     size_t pos = 0;