Text editor

A text editor is a type of program used for editing plain text files. Such programs are sometimes known as "notepad" software, following the Microsoft Notepad.

Text editors are provided with operating systems and software development packages, and can be used to change configuration files, documentation files and programming language source code.

There are important differences between plain text files created by a text editor and document files created by word processors such as Microsoft Word or WordPerfect.

Word processors were developed to allow formatting of text for presentation on a printed page, while text produced by text editors is generally used for other purposes, such as input data for a computer program.

When both formats are available, the user must select with care. Saving a plain text file in a word-processor format adds formatting information that can make the text unreadable by a program that expects plain text. Conversely, saving a word-processor document as plain text removes any formatting information.

Before text editors existed, computer text was punched into cards with keypunch machines. Physical boxes of these thin cardboard cards were then inserted into a card-reader. Magnetic tape and disk "card-image" files created from such card decks often had no line-separation characters at all, and assumed fixed-length 80-character records. An alternative to cards was punched paper tape. It could be created by some teleprinters (such as the Teletype), which used special characters to indicate ends of records.

The first text editors were "line editors" oriented to teleprinter- or typewriter-style terminals without displays. Commands (often a single keystroke) effected edits to a file at an imaginary insertion point called the "cursor". Edits were verified by typing a command to print a small section of the file, and periodically by printing the entire file. In some line editors, the cursor could be moved by commands that specified the line number in the file, text strings (context) for which to search, and eventually regular expressions. Line editors were major improvements over keypunching. Some line editors could be used by keypunch; editing commands could be taken from a deck of cards and applied to a specified file. Some common line editors supported a "verify" mode in which change commands displayed the altered lines.

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