Text editor

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A text editor is a type of program used for editing plain text files.

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


Plain text files vs. word processor files

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

  • A plain text file is represented and edited by showing all the characters as they are present in the file. The only characters usable for 'mark-up' are the control characters of the used character set; in practice this is newline, tab and formfeed. The most commonly used character set is ASCII, especially recently, as plain text files are more often being used for programming and configuration, and less frequently for documentation (e.g. detailed instructions, user guides) than in the past.
  • Documents created by a word processor generally contain fileformat-specific "control characters" beyond what is defined in the character set. They enable functions like bold, italic, fonts, columns, tables, etc. These and other common page formatting symbols were once associated only with desktop publishing, but are now commonplace in the simplest word processor.
  • Word processor programs can usually edit a plain text file and save it back in the plain text file format. However, one must take care to tell the program that this is what is wanted. Specifying the save format is especially important in cases such as source code, HTML, and configuration and control files. If left to the program's default, the file will contain those "special characters" unique to the word processor's file format, and will not be handled correctly by the utility the files were intended for.


Before text editors existed, computer text was punched into punched cards with keypunch machines. The text was carried as a physical box of these thin cardboard cards, and read into a card-reader.

The first text editors were line editors oriented on typewriter style terminals and they did not provide a window or screen-oriented display. They usually had very short commands (to minimize typing) that reproduced the current line. Among them were a command to print a selected section(s) of the file on the typewriter (or printer) in case of necessity. An "edit cursor", an imaginary insertion point, could be moved by special commands that operated with line numbers of specific text strings (context). Later, the context strings were extended to regular expressions. To see the changes, the file needed to be printed on the printer. These "line-based text editors" were considered revolutionary improvements over keypunch machines. In case typewriter-based terminals were not available, they were adapted to keypunch equipment. In this case the user needed to punch the commands into the separate deck of cards and feed them into the computer in order to edit the file.

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