Test files › Filename edge cases

Sample Filename edge cases test files

What are filename edge cases?

File names that break file handling on some system: reserved Windows names such as CON, characters Windows forbids, right-to-left overrides, Unicode in NFC and NFD forms, trailing dots, double extensions and names past length limits. Each file here has one.

26 free filename edge cases test files for QA and developers: .hidden-leading-dot, 🦊-emoji-name.txt, aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa…

File	Format	Size	What it catches
`.hidden-leading-dot`	TXT	142 bytes	Leading dot, no extension - hidden on POSIX.
`🦊-emoji-name.txt`	TXT	142 bytes	Emoji (4-byte UTF-8, outside the BMP) in the filename.
`aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.txt`	TXT	142 bytes	A 204-character filename.
`ampersand&name.txt`	TXT	142 bytes	An ampersand in the filename.
`archive.tar.gz`	TXT	142 bytes	A legitimate compound extension.
`backslash\name.txt`	TXT	142 bytes	A backslash in the filename.
`CON.txt`	TXT	142 bytes	A Windows reserved device name.
`dots.in.the.name.txt`	TXT	142 bytes	Multiple dots.
`double"quote.txt`	TXT	142 bytes	An ASCII double quote in the filename.
`hash#name.txt`	TXT	142 bytes	A hash character in the filename.
`invoice‮gnp.txt`	TXT	142 bytes	Contains a right-to-left override (U+202E) so it renders as "invoicetxt.png".
`nfc-café.txt`	TXT	142 bytes	Precomposed Unicode (NFC): é is a single code point U+00E9.
`nfd-café.txt`	TXT	142 bytes	Decomposed Unicode (NFD): é is e + U+0301 combining acute.
`no-extension-at-all`	TXT	142 bytes	No extension at all.
`NUL.txt`	TXT	142 bytes	Another Windows reserved device name.
`percent%20encoded.txt`	TXT	142 bytes	A literal "%20" sequence in the filename.
`plus+name.txt`	TXT	142 bytes	A plus sign in the filename.
`question?name.txt`	TXT	142 bytes	A question mark in the filename.
`report.pdf.exe`	TXT	142 bytes	Double extension where the real extension is last.
`semicolon;name.txt`	TXT	142 bytes	A semicolon in the filename.
`single'quote.txt`	TXT	142 bytes	An ASCII single quote in the filename.
`spaces in name.txt`	TXT	142 bytes	Spaces in the filename.
`trailing-dot.txt.`	TXT	142 bytes	A trailing dot after the extension.
`UPPERCASE.TXT`	TXT	142 bytes	All-caps name and extension.
`файл-кириллица.txt`	TXT	142 bytes	Cyrillic characters in the filename.
`日本語ファイル名.txt`	TXT	142 bytes	Japanese characters in the filename.

Handle it in code

Each snippet below was run against this exact file with Python 3.14.4 and Node 24.15.0 when this page was built, and the output shown is what it printed.

Python

Check uploaded file names for invisible direction controls and executable double extensions before you store or display them.

import unicodedata

BIDI = {"LRE", "RLE", "PDF", "LRO", "RLO", "LRI", "RLI", "FSI", "PDI"}
RUNS = {"exe", "scr", "bat", "cmd", "com", "js", "vbs", "ps1", "msi", "jar", "lnk"}

def check_name(name):
    problems = []
    if any(unicodedata.bidirectional(c) in BIDI for c in name):
        problems.append("contains an invisible direction control")
    parts = name.lower().split(".")
    if len(parts) > 2 and parts[-1] in RUNS:
        problems.append(f"double extension .{parts[-2]}.{parts[-1]}")
    return problems or ["ok"]

for name in ["invoice\u202Egnp.txt", "report.pdf.exe", "notes.txt"]:
    print(ascii(name), check_name(name))

Run against this file, it prints: 'invoice\u202egnp.txt' ['contains an invisible direction control'] 'report.pdf.exe' ['double extension .pdf.exe'] 'notes.txt' ['ok']

Node.js

The same checks in JavaScript.

const BIDI = /[\u202A-\u202E\u2066-\u2069]/;
const RUNS = new Set(['exe', 'scr', 'bat', 'cmd', 'com', 'js', 'vbs', 'ps1', 'msi', 'jar', 'lnk']);

function checkName(name) {
  const problems = [];
  if (BIDI.test(name)) problems.push('contains an invisible direction control');
  const parts = name.toLowerCase().split('.');
  if (parts.length > 2 && RUNS.has(parts.at(-1))) problems.push('double extension .' + parts.at(-2) + '.' + parts.at(-1));
  return problems.length ? problems : ['ok'];
}

// Print control characters as escapes, so the output cannot reorder itself.
const show = (s) => s.replace(/[\u202A-\u202E\u2066-\u2069]/g, (c) => '\\u' + c.charCodeAt(0).toString(16));

for (const name of ['invoice\u202Egnp.txt', 'report.pdf.exe', 'notes.txt']) {
  console.log(show(name), checkName(name));
}

Run against this file, it prints: invoice\u202egnp.txt [ 'contains an invisible direction control' ] report.pdf.exe [ 'double extension .pdf.exe' ] notes.txt [ 'ok' ]

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