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read_file

The read_file tool examines the contents of files in a project. It allows Roo to understand code, configuration files, and documentation to provide better assistance.

Parameters

The tool accepts these parameters:

  • path (required): The path of the file to read relative to the current working directory
  • start_line (optional): The starting line number to read from (1-based indexing)
  • end_line (optional): The ending line number to read to (1-based, inclusive)

What It Does

This tool reads the content of a specified file and returns it with line numbers for easy reference. It can read entire files or specific sections, and even extract text from PDFs and Word documents.

When is it used?

  • When Roo needs to understand existing code structure
  • When Roo needs to analyze configuration files
  • When Roo needs to extract information from text files
  • When Roo needs to see code before suggesting changes
  • When specific line numbers need to be referenced in discussions

Key Features

  • Displays file content with line numbers for easy reference
  • Can read specific portions of files by specifying line ranges
  • Extracts readable text from PDF and DOCX files
  • Automatically truncates large text files when no line range is specified, showing the beginning of the file
  • Provides method summaries with line ranges for truncated large code files
  • Efficiently streams only requested line ranges for better performance
  • Makes it easy to discuss specific parts of code with line numbering

Limitations

  • May not handle extremely large files efficiently without using line range parameters
  • For binary files (except PDF and DOCX), may return content that isn't human-readable

How It Works

When the read_file tool is invoked, it follows this process:

  1. Parameter Validation: Validates the required path parameter and optional parameters
  2. Path Resolution: Resolves the relative path to an absolute path
  3. Reading Strategy Selection:
    • The tool uses a strict priority hierarchy (explained in detail below)
    • It chooses between range reading, auto-truncation, or full file reading
  4. Content Processing:
    • Adds line numbers to the content (e.g., "1 | const x = 13") where 1 | is the line number.
    • For truncated files, adds truncation notice and method definitions
    • For special formats (PDF, DOCX), extracts readable text

Reading Strategy Priority

The tool uses a clear decision hierarchy to determine how to read a file:

  1. First Priority: Explicit Line Range

    • If either start_line or end_line is provided, the tool always performs a range read
    • The implementation efficiently streams only the requested lines, making it suitable for processing large files
    • This takes precedence over all other options

  2. Second Priority: Automatic Truncation for Large Text Files

    • This applies only when all of the following conditions are met:
      • Neither start_line nor end_line is specified.
      • The file is identified as a text-based file (not binary like PDF/DOCX).
      • The file's total line count exceeds an internal limit (e.g., maxReadFileLine, often around 500 lines).
    • When automatic truncation occurs:
      • The tool reads only the first maxReadFileLine lines.
      • It appends a notice indicating truncation (e.g., [Showing only 500 of 1200 total lines...]).
      • For code files, it may also append a summary of source code definitions found within the truncated portion.

  3. Default Behavior: Read Entire File

    • If neither an explicit range is given nor automatic truncation applies (e.g., the file is within the line limit, or it's a supported binary type), the tool reads the entire content.
    • For supported formats like PDF and DOCX, it attempts to extract the full text content.

Examples When Used

  • When asked to explain or improve code, Roo first reads the relevant files to understand the current implementation.
  • When troubleshooting configuration issues, Roo reads config files to identify potential problems.
  • When working with documentation, Roo reads existing docs to understand the current content before suggesting improvements.

Usage Examples

Here are several scenarios demonstrating how the read_file tool is used and the typical output you might receive.

Reading an Entire File

To read the complete content of a file:

Input:

<read_file>
<path>src/app.js</path>
</read_file>

Simulated Output (for a small file like example_small.txt):

1 | This is the first line.
2 | This is the second line.
3 | This is the third line.

(Output will vary based on the actual file content)

Reading Specific Lines

To read only a specific range of lines (e.g., 46-68):

Input:

<read_file>
<path>src/app.js</path>
<start_line>46</start_line>
<end_line>68</end_line>
</read_file>

Simulated Output (for lines 2-3 of example_five_lines.txt):

2 | Content of line two.
3 | Content of line three.

(Output shows only the requested lines with their original line numbers)

Reading a Large Text File (Automatic Truncation)

When reading a large text file without specifying a line range, the tool automatically truncates the content if it exceeds the internal line limit (e.g., 500 lines).

Input:

<read_file>
<path>logs/large_app.log</path>
</read_file>

Simulated Output (for a 1500-line log file with a 500-line limit):

1 | Log entry 1...
2 | Log entry 2...
...
500 | Log entry 500...

[Showing only 500 of 1500 total lines. Use start_line and end_line to read specific ranges.]
// Optional: Source code definitions summary might appear here for code files

(Output shows the beginning lines up to the internal limit, plus a truncation notice. Use line ranges for full access.)

Attempting to Read a Non-Existent File

If the specified file does not exist:

Input:

<read_file>
<path>non_existent_file.txt</path>
</read_file>

Simulated Output (Error):

Error: File not found at path 'non_existent_file.txt'.

Attempting to Read a Blocked File

If the file is excluded by rules in a .rooignore file:

Input:

<read_file>
<path>.env</path>
</read_file>

Simulated Output (Error):

Error: Access denied to file '.env' due to .rooignore rules.