endofline

End-of-line (EOL) denotes the marker that terminates a line of text in a file or stream. A line is typically the sequence of characters between two EOL markers or between the start of the file and the first EOL. The exact sequence used varies by system and context.

The most common end-of-line conventions are LF (line feed), CRLF (carriage return followed by line feed), and CR (carriage return). LF, represented as the single character 0x0A or the escape sequence \n, is standard on Unix-like systems such as Linux and modern macOS. CRLF, 0x0D0A or \r\n, is used by Windows. CR, 0x0D or \r, was used by classic Mac OS and is now rare.

Historically, end-of-line behavior arose from the mechanics of early teletypewriters, which required separate commands to return the print head and advance the paper. Different platforms adopted different conventions, and the differences persisted as computing evolved into modern text processing.

In practice, mixed line endings can cause problems in editors, version control systems, and build pipelines. Some editors normalize endings automatically; others preserve them. Tools such as dos2unix and unix2dos convert between conventions. Git can be configured with core.autocrlf to manage conversions during checkout and commit.

In programming, newline sequences are expressed in source code as escape sequences, such as \n, \r, or \r\n, depending on the language. Some network protocols and file formats specify a particular EOL sequence, for example HTTP header lines use CRLF.

End-of-line handling is a routine concern in software development and data interchange, impacting text processing, diffs, and cross-platform collaboration. Understanding the local convention and choosing a consistent policy helps ensure predictable behavior across tools and environments.