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Fix File Extension

Reads what a file actually contains and, where that contradicts its extension, renames it with the extension its type normally carries — a PDF saved as .dat becomes .pdf. Useful when a source system hands off files with wrong or missing extensions.

Inputs

Section titled “Inputs”
  • Input File or Directory — a file, or a folder whose files are each checked, in a document account. Files are renamed where they are, so there is no output location.

How It Works

Section titled “How It Works”

The step identifies each file’s type from its contents, and renames the file only when its current name is missing an extension, has a placeholder one (.dat, .tmp or .bin), or names a different type the step recognises.

The types it recognises are PDF; JPEG, PNG, GIF, TIFF, BMP, WebP and HEIC images; Excel (.xlsx, .xls), Word (.docx, .doc) and PowerPoint (.pptx) documents; ZIP and GZip archives; and CSV, JSON, HTML, XML and plain text.

A file keeps its name when:

  • its extension already fits its contents — .jpg and .jpeg both fit a JPEG, .tif and .tiff a TIFF;
  • its extension is one the step doesn’t recognise, such as .sql, .log or .ai, because contents alone cannot tell a SQL script from any other text, or an Illustrator file from a PDF;
  • it holds plain text under a text extension such as .csv, .tsv or .json;
  • it holds one text format under another’s extension — XML in a .html file, CSV in a .json file — because contents can’t reliably tell those apart. Only a .txt file, or one with no or a placeholder extension, is renamed to a text format;
  • it is a ZIP file named as an Office document, since .xlsx, .docx and .pptx files are ZIP files inside;
  • its type cannot be determined, as for an empty file.

An archive is judged by its own contents: its members are not opened or renamed. Files whose names start with . are skipped.

Examples

Section titled “Examples”
File Contents Result
invoice.dat PDF renamed invoice.pdf
photo.png JPEG renamed photo.jpg
export.txt CSV renamed export.csv
readme plain text renamed readme.txt
query.sql plain text unchanged
budget.xlsx ZIP unchanged

Notes

Section titled “Notes”
  • If the input path does not exist or has no files in it, the step finishes with a warning that names the path and processes nothing, and the workflow continues.
Section titled “Related”