CRLF

CRLF stands for carriage return and line feed, the two ASCII control characters 13 and 10 (0x0D and 0x0A). The sequence CRLF is used to indicate the end of a line in a text stream or file.

In text display terms, CR moves the cursor to the start of the current line, and LF advances the display by one line. When used together as CRLF, they move the cursor to the start of the next line. This two-character sequence originated with teletype machines and early terminals and persists in Windows text files and many Internet protocols.

By contrast, Unix-like systems typically use a single LF character for newlines (and macOS historically used CR; modern macOS uses LF). In Windows, text files commonly use CRLF for line endings. Many network protocols, including HTTP, SMTP, and IRC, require CRLF to terminate lines as part of their syntax.

Handling and cross-platform exchange of text can lead to mixed line endings. Editors and tools can normalize endings to LF or CRLF, and version control systems provide options to convert on checkout and commit (for example, Git's core.autocrlf). Awareness of the target platform and protocol requirements helps avoid parsing errors and diffs caused by inconsistent line endings.