fix(file_tools): strip ANSI escape codes from write_file and patch content by teknium1 · Pull Request #2532 · NousResearch/hermes-agent

teknium1 · 2026-03-22T18:16:59Z

Summary

Models occasionally copy ANSI escape sequences from terminal output or display formatting into file content when calling write_file or patch. This breaks shebangs and injects binary characters into scripts.

Fix: Strip ANSI escape codes (CSI, OSC, simple escapes) from:

write_file content
patch old_string, new_string, and V4A patch content

The check is fast — skips entirely if no ESC byte (\x1b) is present in the string.

Reported by Andi Jaeger on X.

Test plan

All 24 file tools tests pass
Strip function verified against colored shebangs, bold/green formatting, clean passthrough

…ntent Models occasionally copy ANSI escape sequences from terminal output or display formatting into file content, breaking shebangs and injecting binary characters into scripts. Strip ANSI codes (CSI, OSC, simple escapes) from: - write_file content - patch old_string, new_string, and V4A patch content The check is fast (skips entirely if no ESC byte present). Reported by Andi Jaeger.

…es the model Root cause: terminal_tool, execute_code, and process_registry returned raw subprocess output with ANSI escape sequences intact. The model saw these in tool results and copied them into file writes. Previous fix (PR #2532) stripped ANSI at the write point in file_tools.py, but this was a band-aid — regex on file content risks corrupting legitimate content, and doesn't prevent ANSI from wasting tokens in the model context. Source-level fix: - New tools/ansi_strip.py with comprehensive ECMA-48 regex covering CSI (incl. private-mode, colon-separated, intermediate bytes), OSC (both terminators), DCS/SOS/PM/APC strings, Fp/Fe/Fs/nF escapes, 8-bit C1 - terminal_tool.py: strip output before returning to model - code_execution_tool.py: strip stdout/stderr before returning - process_registry.py: strip output in poll/read_log/wait - file_tools.py: remove _strip_ansi band-aid (no longer needed) Verified: `ls --color=always` output returned as clean text to model, file written from that output contains zero ESC bytes.

…es the model Root cause: terminal_tool, execute_code, and process_registry returned raw subprocess output with ANSI escape sequences intact. The model saw these in tool results and copied them into file writes. Previous fix (PR NousResearch#2532) stripped ANSI at the write point in file_tools.py, but this was a band-aid — regex on file content risks corrupting legitimate content, and doesn't prevent ANSI from wasting tokens in the model context. Source-level fix: - New tools/ansi_strip.py with comprehensive ECMA-48 regex covering CSI (incl. private-mode, colon-separated, intermediate bytes), OSC (both terminators), DCS/SOS/PM/APC strings, Fp/Fe/Fs/nF escapes, 8-bit C1 - terminal_tool.py: strip output before returning to model - code_execution_tool.py: strip stdout/stderr before returning - process_registry.py: strip output in poll/read_log/wait - file_tools.py: remove _strip_ansi band-aid (no longer needed) Verified: `ls --color=always` output returned as clean text to model, file written from that output contains zero ESC bytes.

…ntent (NousResearch#2532) Models occasionally copy ANSI escape sequences from terminal output or display formatting into file content, breaking shebangs and injecting binary characters into scripts. Strip ANSI codes (CSI, OSC, simple escapes) from: - write_file content - patch old_string, new_string, and V4A patch content The check is fast (skips entirely if no ESC byte present). Reported by Andi Jaeger.