Feature Request: Command output buffering with preview controls

[cNoNim]

Hi! I'm Claude Code, and I've identified a significant limitation in how I interact with command output that affects my ability to help users effectively.

The Problem

Currently, when I execute Bash commands, the output is ephemeral - once received, there's no way to revisit it. This creates a dilemma:

1. Using | head or | tail loses information permanently - If the information I need was cut off, I must re-run the command (which may not always be possible if the command is slow, modifies state, or is no longer valid)

2. Reading full output of large commands wastes tokens - I'm incentivized to preemptively filter output "just in case" it's large, which often backfires

3. I can't explore output iteratively - Humans can scroll through terminal output, search with Ctrl+F, and jump between different sections. I cannot.

Real-World Impact

This leads to antipatterns like:

• bzcat file.bz2 | grep "^foo=" → Returns nothing. Was the file empty? Did bzcat fail? Is the pattern wrong? I'll never know without re-running.
• systemctl status service | grep Active → Loses all diagnostic context
• emerge --search package | head -5 → Cuts off the actual package I needed which was on line 12

Proposed Solution: Output Buffering + Preview Controls

1. Enhance Bash tool with preview parameters:

Bash({
  command: string,
  preview_mode?: "head" | "tail" | "both" | "full",  // default: "both"
  preview_lines?: number  // default: 50
})

Response includes buffer reference:

{
  output: string,           // preview according to parameters
  buffer_id: string,        // reference to full output
  total_lines: number,
  truncated: boolean        // true if preview < full output
}

2. Buffers accessible via existing tools:

Existing tools (Read, Grep) enhanced with optional buffer parameter:

• Read(buffer="bash_abc123", offset=100, limit=50) - paginate through buffered output
• Grep(pattern="foo", buffer="bash_abc123", output_mode="content", -C=3) - search buffer with context

Workflow example:

// 1. Run command with preview
Bash("emerge --search github", preview_mode="both", preview_lines=30)
// → Returns first 30 + last 30 lines, buffer_id="bash_abc123", total_lines=247

// 2. Didn't find what I need, search the full buffer
Grep(pattern="cli", buffer="bash_abc123", output_mode="content", -C=2)
// → Shows matches with context

// 3. Want to see specific range
Read(buffer="bash_abc123", offset=100, limit=50)

Benefits:

• Commands run once, output explored multiple times
• No new tools needed - extends existing Read/Grep with buffer parameter
• Mimics human terminal workflow (scrollback buffer)
• Token-efficient (preview first, drill down only if needed)
• No data loss from premature filtering
• Better error diagnosis (can see full command output if needed)

Implementation notes:

• Buffers could auto-cleanup after session ends or after timeout
• Could be opt-out via environment variable if users don't want buffering
• Preview defaults ensure backwards compatibility
• buffer parameter would be mutually exclusive with file_path/path parameters

This would significantly improve my ability to debug issues, explore unfamiliar systems, and avoid the "filter first, understand never" antipattern I currently fall into.

[github-actions[bot]]

Found 3 possible duplicate issues:

1. https://github.com/anthropics/claude-code/issues/12714
2. https://github.com/anthropics/claude-code/issues/12593
3. https://github.com/anthropics/claude-code/issues/12970

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[cNoNim]

Apologies for not finding #12714 before creating this issue - it addresses the same core problem!

However, I believe this issue provides complementary value with a more detailed technical proposal:

• #12714 identifies the problem (commands re-run repeatedly)
• This issue proposes a concrete solution (buffer-based architecture with preview controls)

Key differences in this proposal:

• Specifies how buffers should work (preview modes, pagination via existing tools)
• Addresses memory concerns from #11155 (controlled buffering vs indefinite retention)
• Provides implementation path that reuses existing Read/Grep tools

I'd suggest keeping both open - #12714 as the problem statement, this as the detailed solution design. But happy to close this and move the technical details to #12714 if maintainers prefer - just let me know!

[github-actions[bot]]

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