In computing, “end of line” (EOL) is the boundary that marks where one line of text stops and the next begins. It is not one fixed character. Internet protocols commonly use the two-character sequence CR-LF, while many programming languages and operating systems use LF alone. The correct EOL is whichever one the file format, protocol, language, or device you are working with requires.
What “end of line” actually refers to
An end-of-line marker is a control character or pair of control characters placed in a text stream to signal that the current line is finished. Software that reads or writes text uses that marker to split content into lines, to position a cursor or printing point, and to decide where a record ends. Because the marker is a convention rather than a universal standard, the same visible text can be stored with different bytes depending on where it came from.
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RFC 1849 makes this point directly. Its section 2.4 states: “How the end of a text line is represented depends on the context and the implementation.” That single sentence explains most of the confusion around the term. “EOL” tells you that a line boundary exists; it does not tell you which bytes represent it.
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CR and LF: two control characters with different effects
Most EOL conventions are built from two ASCII control characters, carriage return (CR) and line feed (LF). They do different jobs, and it helps to keep them separate before looking at combinations.
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Carriage return (CR)
National Instruments’ LabVIEW documentation describes CR as moving the cursor to the beginning of the current line without advancing to the next line. It gives the value as decimal 13, hexadecimal 0x0D. That is a vendor description of LabVIEW’s character handling, not a statement about how every terminal or device behaves.
Line feed (LF)
The same LabVIEW documentation describes LF as moving the cursor down to the next line without returning it to the beginning of the line, with the value decimal 10, hexadecimal 0x0A. RFC 1849 notes that ISO C and many modern operating systems indicate end-of-line with a single character, typically ASCII LF.
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A US federal ASCII standard amendment gives LF a printing meaning in one context. Where appropriate, the character “may have the meaning ‘New Line’ (NL), a format effector which controls the movement of the printing point to the first printing position on the next printing line.” This wording describes LF in printing terms, which is one reason the character is associated with moving to a new line rather than only with the text itself.
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CR-LF uses both characters in order: CR first, then LF. The sequence therefore returns the cursor to the start of the line and advances it to the next line in a single end-of-line marker. Three sources describe this pairing in different contexts:
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- Telnet. RFC 318, “The End of the Line Convention,” written by John Postel in April 1972, states: “The end of a line of text shall be indicated by the character sequence Carriage Return Line Feed (CR, LF).” That rule governs Telnet, not every file or operating system.
- Internet transmission. RFC 1849 describes CR (ASCII 13) followed by LF (ASCII 10) for Internet transmission, with SMTP given as an example.
- LabVIEW. National Instruments names the CR-LF pair its End of Line character constant in LabVIEW. This is a platform-specific naming choice.
These are context-specific descriptions. They do not show that every platform uses CR-LF, and they should not be read as a universal rule.
Where each convention appears
The table below summarizes the conventions the cited sources document. Cells marked “not stated” mean the source you would need to check does not establish that detail.
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| Convention | Characters | Effect described | Documented context | Source |
|---|---|---|---|---|
| CR | ASCII 13 (0x0D) | Moves cursor to start of line; no advance | LabVIEW character handling | National Instruments LabVIEW documentation |
| LF | ASCII 10 (0x0A) | Moves cursor down; no return to start of line | ISO C and many modern operating systems, per RFC 1849; LabVIEW | RFC 1849; National Instruments LabVIEW documentation |
| CR-LF | ASCII 13 followed by ASCII 10 | Returns to start of line and advances to next line | Telnet end-of-line convention; Internet transmission such as SMTP; LabVIEW End of Line constant | RFC 318; RFC 1849; National Instruments LabVIEW documentation |
| Printing meaning of LF | ASCII 10 | New Line: moves printing point to first printing position on next line | US federal ASCII standard amendment, where appropriate | Federal ASCII standard amendment |
How to choose and handle the right convention
When you write or parse text, the safe approach is to follow the rule of the thing you are interacting with rather than the label “EOL.” The sources support the following sequence of checks:
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- Read that context’s own documentation for its line-ending rule. For a protocol, that is the protocol specification; for a language, its runtime or library reference; for hardware, the device manual or driver documentation.
- When writing, emit exactly the sequence that documentation requires, whether that is CR-LF, LF, or another form.
- When reading, do not assume one representation. A parser written for LF-only input can leave stray CR characters at the end of each line when it receives CR-LF input, and a parser written only for CR-LF can fail to split LF-only input cleanly. Test with both forms if the source is not under your control.
What the sources do and do not establish
The definition of end of line is stable across these sources. The specifics are less uniform. RFC 318 dates from 1972 and describes Telnet. RFC 1849 emphasizes that representation depends on context and implementation, and it does not supply a single universal character. The National Instruments material is explicitly LabVIEW-specific and reflects that vendor’s terminology. None of these sources, taken together, establishes which line ending a particular modern tool, editor, or operating system version uses by default; for that, consult the documentation of the exact product and version you are working with.
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No population statistics or survey figures apply to this definition. The only numeric values are the character codes listed above, which are fixed by ASCII.
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