-e/--extension feature, closes simonw#28

README.md

@@ -29,6 +29,12 @@ This will output the contents of every file, with each file preceded by its rela
 
 ### Options
 
+- `-e/--extension <extension>`: Only include files with the specified extension. Can be used multiple times.
+
+  ```bash
+  files-to-prompt path/to/directory -e txt -e md
+  ```
+
 - `--include-hidden`: Include files and folders starting with `.` (hidden files and directories).
 
   ```bash

files_to_prompt/cli.py

@@ -53,6 +53,7 @@ def print_as_xml(writer, path, content):
 
 def process_path(
     path,
+    extensions,
     include_hidden,
     ignore_gitignore,
     gitignore_rules,
@@ -93,6 +94,9 @@ def process_path(
                     if not any(fnmatch(f, pattern) for pattern in ignore_patterns)
                 ]
 
+            if extensions:
+                files = [f for f in files if f.endswith(extensions)]
+
             for file in sorted(files):
                 file_path = os.path.join(root, file)
                 try:
@@ -107,6 +111,7 @@ def process_path(
 
 @click.command()
 @click.argument("paths", nargs=-1, type=click.Path(exists=True))
+@click.option("extensions", "-e", "--extension", multiple=True)
 @click.option(
     "--include-hidden",
     is_flag=True,
@@ -140,7 +145,13 @@ def process_path(
 )
 @click.version_option()
 def cli(
-    paths, include_hidden, ignore_gitignore, ignore_patterns, output_file, claude_xml
+    paths,
+    extensions,
+    include_hidden,
+    ignore_gitignore,
+    ignore_patterns,
+    output_file,
+    claude_xml,
 ):
     """
     Takes one or more paths to files or directories and outputs every file,
@@ -186,6 +197,7 @@ def cli(
             writer("<documents>")
         process_path(
             path,
+            extensions,
             include_hidden,
             ignore_gitignore,
             gitignore_rules,

tests/test_files_to_prompt.py

@@ -108,6 +108,31 @@ def test_ignore_patterns(tmpdir):
         assert "This file should be included" in result.output
 
 
+def test_specific_extensions(tmpdir):
+    runner = CliRunner()
+    with tmpdir.as_cwd():
+        # Write one.txt one.py two/two.txt two/two.py three.md
+        os.makedirs("test_dir/two")
+        with open("test_dir/one.txt", "w") as f:
+            f.write("This is one.txt")
+        with open("test_dir/one.py", "w") as f:
+            f.write("This is one.py")
+        with open("test_dir/two/two.txt", "w") as f:
+            f.write("This is two/two.txt")
+        with open("test_dir/two/two.py", "w") as f:
+            f.write("This is two/two.py")
+        with open("test_dir/three.md", "w") as f:
+            f.write("This is three.md")
+
+        # Try with -e py -e md
+        result = runner.invoke(cli, ["test_dir", "-e", "py", "-e", "md"])
+        assert result.exit_code == 0
+        assert ".txt" not in result.output
+        assert "test_dir/one.py" in result.output
+        assert "test_dir/two/two.py" in result.output
+        assert "test_dir/three.md" in result.output
+
+
 def test_mixed_paths_with_options(tmpdir):
     runner = CliRunner()
     with tmpdir.as_cwd():