READ FILE LINES

Reads a contiguous range of lines from a file attachment using memory-safe streaming (fopen/fgets), returning the content with padded line-number prefixes. Accepts a numeric attachment ID, a file path, or an attachment name. Use this worker when you need to inspect or pass a specific slice of a large text file without loading it entirely into memory.

When to use

Tagged: attachment, file, file_read, large_file, line_range, streaming, text.

Inputs

Label	ID	Type	Default	Required	Description
File	file	file	—	✓	The file to read — supply a numeric attachment ID, an absolute/relative file path, or an attachment name; this field is required.
Start Line	start_line	number	1		1-based line number at which reading begins; defaults to 1 (first line of the file).
End Line	end_line	number	—		1-based line number at which reading stops (inclusive); leave blank to read until max_lines or end-of-file.
Max Lines	max_lines	number	500		Hard cap on the number of lines returned to prevent context overflow; defaults to 500 — increase only when a larger slice is explicitly needed.

Outputs

Label	ID	Type	Description
Content	content	text	The extracted lines as a single newline-delimited string, each prefixed with a right-aligned 6-character line number and a pipe separator (e.g., ‘ 7/line text’).
Total Lines	total_lines	number	Total number of lines in the file (counted by streaming the remainder after the requested range), regardless of how many were returned.
Lines Read	lines_read	number	Actual number of lines collected and included in content — may be less than the requested range when max_lines or end-of-file is reached first.
Start Line Actual	start_line_actual	number	The 1-based line number where reading actually began (reflects any clamping of the start_line input to a minimum of 1).
End Line Actual	end_line_actual	number	The 1-based line number of the last line included in content.
Status	status	string	Human-readable result message, e.g. ‘Success: Read 42 lines from myfile.txt (total: 1200 lines)’; non-empty on success, replaced by an error message on failure.

Disciplines

• data.io.file

---

Auto-generated from platform schema. Worker id: file_read. Schema hash: d1bbe85155af. Hand-curated docs in workerexamples/ override this page when present.