lineending

Line ending, also called end-of-line (EOL) or newline, refers to a character or sequence signaling the end of a line of text. It marks where one line ends and the next begins in files and data streams. The exact characters vary by system: Unix-like systems use a single line feed character LF (U+000A). Windows uses a carriage return followed by a line feed CRLF (U+000D U+000A). Classic Mac OS used a single carriage return CR (U+000D) for line termination in older days.

The concept originates from typewriter and teleprinter controls, where CR returned the print head and LF moved to the next line; combining both allowed separate horizontal and vertical movements. In practice, line endings affect editors, compilers, diff tools, and version control. Mixed line endings in a file can cause issues in diffs or builds. Common remedies include normalizing to a single convention, using tools like dos2unix, unix2dos, or editor settings that convert on save. Version control systems offer automatic normalization, for example Git’s core.autocrlf feature, to translate endings on checkout or commit.

When files are transferred between systems, line endings may be converted depending on the transfer mode (text versus binary). Some languages and protocols treat newline as a control character within strings, with environments choosing representations such as \n (LF) or \r\n (CRLF) in source code or data.

Handling: editors may detect and preserve or convert endings, display them, or normalize on save. The choice of line ending affects cross-platform collaboration, patch formats, and build scripts, and is typically governed by project conventions.