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(pronounced as distinct letters, ) is a line editor for
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, ...
and
Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
operating systems. It was one of the first parts of the Unix operating system that was developed, in August 1969. It remains part of the
POSIX The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming in ...
and Open Group standards for Unix-based operating systems, alongside the more sophisticated full-screen editor vi.


History and influence

The ed text editor was one of the first three key elements of the Unix operating system— assembler,
editor Editing is the process of selecting and preparing written, photographic, visual, audible, or cinematic material used by a person or an entity to convey a message or information. The editing process can involve correction, condensation, or ...
, and shell—developed by Ken Thompson in August 1969 on a PDP-7 at AT&T Bell Labs. Many features of ed came from the qed text editor developed at Thompson's alma mater
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant un ...
. Thompson was very familiar with qed, and had reimplemented it on the CTSS and
Multics Multics ("Multiplexed Information and Computing Service") is an influential early time-sharing operating system based on the concept of a single-level memory.Dennis M. Ritchie, "The Evolution of the Unix Time-sharing System", Communications of ...
systems. Thompson's versions of qed were notable as the first to implement
regular expression A regular expression (shortened as regex or regexp; sometimes referred to as rational expression) is a sequence of characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" ...
s. Regular expressions are also implemented in ed, though their implementation is considerably less general than that in qed. Dennis M. Ritchie produced what Doug McIlroy later described as the "definitive" ed, and aspects of ed went on to influence ex, which in turn spawned vi. The non-interactive Unix command
grep grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. Its name comes from the ed command ''g/re/p'' (''globally search for a regular expression and print matching lines''), which has the sa ...
was inspired by a common special use of qed and later ed, where the command g/re/p means globally search for the regular expression re and print the lines containing it. The Unix stream editor, sed implemented many of the scripting features of qed that were not supported by ed on Unix.


Features

Features of ed include: * available on essentially all Unix systems (and mandatory on systems conforming to the Single Unix Specification). * support for
regular expression A regular expression (shortened as regex or regexp; sometimes referred to as rational expression) is a sequence of characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" ...
s * powerful automation can be achieved by feeding commands from standard input (In)famous for its terseness, ed gives almost no visual feedback, and has been called (by
Peter H. Salus Peter Henry Salus is a linguist, computer scientist, historian of technology, author in many fields, and an editor of books and journals. He has conducted research in germanistics, language acquisition, and computer languages. Education and c ...
) "the most user-hostile editor ever created", even when compared to the contemporary (and notoriously complex) TECO. For example, the message that ed will produce in case of error, ''and'' when it wants to make sure the user wishes to quit without saving, is "?". It does not report the current filename or line number, or even display the results of a change to the text, unless requested. Older versions (c. 1981) did not even ask for confirmation when a quit command was issued without the user saving changes. This terseness was appropriate in the early versions of Unix, when consoles were teletypes,
modem A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by modulating one or more c ...
s were slow, and
memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remember ...
was precious. As computer technology improved and these constraints were loosened, editors with more visual feedback became the norm. In current practice, ed is rarely used interactively, but does find use in some
shell script A shell script is a computer program designed to be run by a Unix shell, a command-line interpreter. The various dialects of shell scripts are considered to be scripting languages. Typical operations performed by shell scripts include file man ...
s. For interactive use, ed was subsumed by the sam, vi and
Emacs Emacs , originally named EMACS (an acronym for "Editor MACroS"), is a family of text editors that are characterized by their extensibility. The manual for the most widely used variant, GNU Emacs, describes it as "the extensible, customizable, ...
editors in the 1980s. ed can be found on virtually every version of Unix and
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...
available, and as such is useful for people who have to work with multiple versions of Unix. On Unix-based operating systems, some utilities like SQL*Plus run ed as the editor if the EDITOR and VISUAL environment variables are not defined. If something goes wrong, ed is sometimes the only editor available. This is often the only time when it is used interactively. The version of ed provided by
GNU GNU () is an extensive collection of free software (383 packages as of January 2022), which can be used as an operating system or can be used in parts with other operating systems. The use of the completed GNU tools led to the family of operat ...
has a few switches to enhance the feedback. Using provides a simple prompt and enables more useful feedback messages. The switch is defined in POSIX since XPG2 (1987). The ed commands are often imitated in other line-based editors. For example, EDLIN in early
MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few o ...
versions and
32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in 32- bit units. Compared to smaller bit widths, 32-bit computers can perform large calculati ...
versions of
Windows NT Windows NT is a proprietary graphical operating system produced by Microsoft, the first version of which was released on July 27, 1993. It is a processor-independent, multiprocessing and multi-user operating system. The first version of Win ...
has a somewhat similar syntax, and text editors in many MUDs (
LPMud LPMud, abbreviated LP, is a family of MUD server software. Its first instance, the original LPMud game driver, was developed in 1989 by Lars Pensjö (hence the LP in LPMud). LPMud was innovative in its separation of the MUD infrastructure into ...
and descendants, for example) use ed-like syntax. These editors, however, are typically more limited in function.


Example

Here is an example transcript of an ed session. For clarity, commands and text typed by the user are in normal face, and output from ed is emphasized. a This is line number two. . 2i   . ,l ed is the standard Unix text editor.$ $ This is line number two.$ 3s/two/three/ ,l ed is the standard Unix text editor.$ $ This is line number three.$ w text 65 q The end result is a simple text file containing the following text: ed is the standard Unix text editor.   This is line number three. Started with an empty file, the a command appends text (all ed commands are single letters). The command puts ed in ''insert mode'', inserting the characters that follow and is terminated by a single dot on a line. The two lines that are entered before the dot end up in the file buffer. The 2i command also goes into insert mode, and will insert the entered text (a single empty line in our case) before line two. All commands may be prefixed by a line number to operate on that line. In the line ,l, the lowercase L stands for the list command. The command is prefixed by a range, in this case , which is a shortcut for 1,$. A range is two line numbers separated by a comma ($ means the last line). In return, ed lists all lines, from first to last. These lines are ended with dollar signs, so that white space at the end of lines is clearly visible. Once the empty line is inserted in line 2, the line which reads "This is line number two." is now actually the third line. This error is corrected with 3s/two/three/, a substitution command. The 3 will apply it to the correct line; following the command is the text to be replaced, and then the replacement. Listing all lines with ,l the line is shown now to be correct. w text writes the buffer to the file "text" making ed respond with ''65'', the number of characters written to the file. q will end an ed session.


Cultural references

The
GNU GNU () is an extensive collection of free software (383 packages as of January 2022), which can be used as an operating system or can be used in parts with other operating systems. The use of the completed GNU tools led to the family of operat ...
project has numerous jokes around ed hosted on its website. In addition, the
glibc The GNU C Library, commonly known as glibc, is the GNU Project's implementation of the C standard library. Despite its name, it now also directly supports C++ (and, indirectly, other programming languages). It was started in the 1980s ...
documentation notes an error code called with its description (errorstr) merely a single question mark, noting "the experienced user will know what is wrong."


See also

* Edlin, the standard MS-DOS line editor which was inspired by ''ed'' *
Sam (text editor) Sam is a multi-file text editor based on structural regular expressions. It was originally designed in the early 1980s at Bell Labs by Rob Pike with the help of Ken Thompson and other Unix developers for the Blit windowing terminal running o ...
* Editor war * List of Unix commands


References


External links

*
Manual page from Unix First Edition describing ed
* * , a direct descendant of the original ed.



section 3.1 describes the history of ed. {{Ken Thompson navbox Unix text editors MacOS text editors Standard Unix programs Unix SUS2008 utilities Plan 9 commands Line editor 1971 software Console applications