line0

Line0 is a term used in computing to refer to the first line of a text stream or data sequence, commonly written as line0 in code. The term arises from zero-based indexing used by many programming languages, where the first element has index 0.

In software development, line0 is often used as a variable name to store or reference the initial line of input, file, or buffer. Some languages and libraries expose zero-based line numbers in their APIs or error reporting, while user-facing messages may shift to 1-based numbering for readability.

Contexts where line0 appears include source code parsers and compilers, text editors and integrated development environments (IDEs) where internal line numbers may start at 0, and patch or diff formats where the original zero-line baseline is indicated (for example, hunks with -0,0). It is also used in data processing pipelines that iterate over lines in a stream, with line0 marking the starting position before any lines have been read.

Because line0 is not a formal standard, its exact meaning depends on the tool or language. When documenting software or sharing code, it is advisable to clarify whether line0 refers to the first line (index 0) or the first line presented to the user (line 1).