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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallUse byte-level checks on the string itself: strpos($string, "rn") detects CRLF, while strpos($string, "r") and strpos($string, "n") detect carriage return and line feed bytes. Check CRLF first when you need to distinguish newline conventions. fopen() text mode does not inspect an existing PHP string; on Windows it translates line endings while a file stream is read or written.
Check for CR, CRLF, and LF in a PHP string
PHP strings are byte buffers without an intrinsic text encoding. In a double-quoted string, r is carriage return (byte 0x0D) and n is line feed (byte 0x0A). Byte-oriented functions such as strpos() can therefore search for these sequences directly. See the PHP string documentation.
$hasCR = strpos($string, "r") !== false;
$hasCRLF = strpos($string, "rn") !== false;
$hasLF = strpos($string, "n") !== false;The strict comparison with false matters because a match at position zero is valid.
Classify the newline convention
A CRLF ending contains both a CR and an LF. Independent checks can therefore report all three flags as true for the same data. Test the two-byte CRLF sequence before testing individual bytes:
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if (strpos($string, "rn") !== false) {
$style = 'CRLF';
} elseif (strpos($string, "r") !== false) {
$style = 'CR';
} elseif (strpos($string, "n") !== false) {
$style = 'LF';
} else {
$style = 'none';
}This reports the first convention found, not whether the entire string is uniform. A file containing mixed endings needs an additional policy: reject it, normalize it, or count each sequence.
Detect a lone CR
To find a carriage return that is not part of CRLF, remove or skip CRLF pairs before searching for r:
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$hasCRLF = strpos($string, "rn") !== false;
$withoutCRLF = str_replace("rn", '', $string);
$hasLoneCR = strpos($withoutCRLF, "r") !== false;
$hasLF = strpos($string, "n") !== false;Use this distinction when legacy Mac-style CR line breaks must be treated differently from Windows-style CRLF.
Reading a file without changing its original bytes
If the bytes come from a file and you need to inspect the original line endings, read it without text translation, then apply the same checks:
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$data = file_get_contents($path);
if ($data === false) {
throw new RuntimeException('Could not read file');
}
$hasCRLF = strpos($data, "rn") !== false;
$hasCR = strpos($data, "r") !== false;
$hasLF = strpos($data, "n") !== false;For an explicit stream, use binary mode (for example, fopen($path, 'rb')) when byte preservation is required. The PHP fopen() manual recommends explicit line endings and binary mode for portable handling.
Scanning a large file in chunks
file_get_contents() is convenient for manageable files but loads the whole file into memory. A chunked scanner must retain a trailing CR from each chunk: the next chunk may begin with LF, forming a CRLF pair across the boundary. Without that carry-over byte, the pair can be misclassified as separate data.
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For line-oriented reads, fgets() reads through a newline. However, the old auto_detect_line_endings setting was deprecated in PHP 8.1; if CR-only lines matter, handle r explicitly instead of relying on that setting. See the fgets() documentation.
What does fopen($path, 't') do?
The t modifier requests Windows text-stream translation. It affects file I/O, not a string already held in memory. On Windows, text mode can translate LF to CRLF when writing and CRLF to LF when reading. This behavior is described in the PHP fopen() manual and Microsoft’s C runtime fopen documentation.
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Why t is not a detection method
- It cannot reveal which bytes were originally present in an in-memory string.
- Reading through translation may change the bytes before your PHP code sees them.
- Text translation can damage binary data.
- Behavior is platform-specific, so it is unsuitable for portable byte inspection.
For portability, the PHP 8.1 deprecations RFC says: “For portability, it is also strongly recommended that you re-write code that uses or relies upon the ‘t’ mode so that it uses the correct line endings and ‘b’ mode instead.” Read the PHP 8.1 deprecations RFC.
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Choose the mode based on your goal
| Goal | Recommended approach | Reason |
|---|---|---|
| Inspect an existing PHP string | strpos($string, "rn"), strpos($string, "r"), and strpos($string, "n") |
Checks the bytes already in memory |
| Preserve file bytes for inspection | fopen($path, 'rb') or file_get_contents() |
Avoids text translation |
| Write portable text output | Choose and write the desired n or rn explicitly |
Makes the output convention intentional |
| Read ordinary text where platform translation is deliberately wanted | Use text mode only with a Windows-specific requirement | t changes stream bytes and is not portable |
Common mistakes
- Searching for the literal characters backslash-plus-
rinstead of the carriage-return byte. Use double quotes:"r". - Checking for
rbeforernwhen classifying styles, which labels CRLF as CR. - Using
fopen()to inspect a string that is already in memory. - Reading a file through translation and then assuming the result represents its original bytes.
- Assuming one detected sequence proves every line uses that convention.
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