Ed (text editor)
Encyclopedia
ed is a line editor
for the Unix
operating system. It was one of the first end-user programs hosted on the system and has been standard in Unix-based systems ever since. ed was originally written in PDP-11
/20 assembler by Ken Thompson in 1971. Ken Thompson was very familiar with an earlier editor known as qed
from University of California at Berkeley, Ken Thompson's alma mater
; he reimplemented qed on the CTSS and Multics
systems, so it is natural that he carried many features of qed forward into ed. Ken Thompson's versions of qed were the first to implement regular expression
s, an idea that had previously been formalized in a mathematical paper, which Ken Thompson had read. The implementation of regular expressions in ed is considerably less general than the implementation in qed.
ed went on to influence ex, which in turn spawned vi
. The non-interactive Unix command grep
was inspired by a common special uses 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; sed, in turn, influenced the design of the programming language AWK, which in turn inspired aspects of Perl
.
Famous for its terseness, ed gives almost no visual feedback. For example, the message that ed will produce in case of error, or 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. This terseness was appropriate in the early versions of Unix, when consoles were teletypes, modem
s were slow, and memory was precious. As computer technology improved and these constraints were loosened, editors with more visual feedback became the standard.
In current practice, ed is rarely used interactively, but does find use in some shell script
s. For interactive use, ed was subsumed by the sam, vi
and Emacs
editors in the 1980s. ed can be found on virtually every version of Unix and Linux
available, and as such is useful for people who have to work with multiple versions of Unix. If something goes wrong, ed is sometimes the only editor available. This is often the only time when it is used interactively.
The ed commands are often imitated in other line-based editors. For example, EDLIN
in early MS-DOS
versions and 32-bit
versions of Windows NT
has a somewhat similar syntax, and text editors in many MUD
s (LPMud
and descendants, for example) use ed-like syntax. These editors, however, are typically more limited in function.
a
ed is the standard Unix text editor.
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 put 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 (a lone comma is also a synonym for %) 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.
proponents used to say, "even Bill Joy
doesn't use vi anymore."
In a 1984 interview Bill Joy explained that, at Sun
, he used an early desktop publishing program, called Interleaf
;
when visiting labs outside Sun, he used plain old ed. Although vi was almost ubiquitous, he could not count on the local version working the way he expected. However, ed was never modified, so he could rely on a consistent experience.
Line editor
A line editor is a text editor computer program that manipulates text primarily by the display, modification, and movement of lines. Line editors precede screen-based text editors and originated in an era when a computer operator typically interacted with a teleprinter , with no video display, and...
for the Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
operating system. It was one of the first end-user programs hosted on the system and has been standard in Unix-based systems ever since. ed was originally written in PDP-11
PDP-11
The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...
/20 assembler by Ken Thompson in 1971. Ken Thompson was very familiar with an earlier editor known as qed
QED (text editor)
QED is a line-oriented computer text editor that was developed by Butler Lampson and L. Peter Deutsch for the Berkeley Timesharing System running on the SDS 940. It was implemented by L...
from University of California at Berkeley, Ken Thompson's alma mater
Alma mater
Alma mater , pronounced ), was used in ancient Rome as a title for various mother goddesses, especially Ceres or Cybele, and in Christianity for the Virgin Mary.-General term:...
; he reimplemented qed on the CTSS and Multics
Multics
Multics was an influential early time-sharing operating system. The project was started in 1964 in Cambridge, Massachusetts...
systems, so it is natural that he carried many features of qed forward into ed. Ken Thompson's versions of qed were the first to implement regular expression
Regular expression
In computing, a regular expression provides a concise and flexible means for "matching" strings of text, such as particular characters, words, or patterns of characters. Abbreviations for "regular expression" include "regex" and "regexp"...
s, an idea that had previously been formalized in a mathematical paper, which Ken Thompson had read. The implementation of regular expressions in ed is considerably less general than the implementation in qed.
ed went on to influence ex, which in turn spawned vi
Vi
vi is a screen-oriented text editor originally created for the Unix operating system. The portable subset of the behavior of vi and programs based on it, and the ex editor language supported within these programs, is described by the Single Unix Specification and POSIX.The original code for vi...
. The non-interactive Unix command grep
Grep
grep is a command-line text-search utility originally written for Unix. The name comes from the ed command g/re/p...
was inspired by a common special uses 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
Sed
sed is a Unix utility that parses text and implements a programming language which can apply transformations to such text. It reads input line by line , applying the operation which has been specified via the command line , and then outputs the line. It was developed from 1973 to 1974 as a Unix...
implemented many of the scripting features of qed that were not supported by ed on Unix; sed, in turn, influenced the design of the programming language AWK, which in turn inspired aspects of Perl
Perl
Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...
.
Features
Features of ed include:- available on essentially all Unix systems (and mandatory on systems conforming to the Single Unix SpecificationSingle UNIX SpecificationThe Single UNIX Specification is the collective name of a family of standards for computer operating systems to qualify for the name "Unix"...
). - a modal editor supporting command mode, text mode and viewing mode
- support for regular expressionRegular expressionIn computing, a regular expression provides a concise and flexible means for "matching" strings of text, such as particular characters, words, or patterns of characters. Abbreviations for "regular expression" include "regex" and "regexp"...
s - powerful automation can be achieved by feeding commands from standard input
Famous for its terseness, ed gives almost no visual feedback. For example, the message that ed will produce in case of error, or 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. This terseness was appropriate in the early versions of Unix, when consoles were teletypes, modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s were slow, and memory was precious. As computer technology improved and these constraints were loosened, editors with more visual feedback became the standard.
In current practice, ed is rarely used interactively, but does find use in some shell script
Shell script
A shell script is a script written for the shell, or command line interpreter, of an operating system. It is often considered a simple domain-specific programming language...
s. For interactive use, ed was subsumed by the sam, vi
Vi
vi is a screen-oriented text editor originally created for the Unix operating system. The portable subset of the behavior of vi and programs based on it, and the ex editor language supported within these programs, is described by the Single Unix Specification and POSIX.The original code for vi...
and Emacs
Emacs
Emacs is a class of text editors, usually characterized by their extensibility. GNU Emacs has over 1,000 commands. It also allows the user to combine these commands into macros to automate work.Development began in the mid-1970s and continues actively...
editors in the 1980s. ed can be found on virtually every version of Unix and Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
available, and as such is useful for people who have to work with multiple versions of Unix. If something goes wrong, ed is sometimes the only editor available. This is often the only time when it is used interactively.
The ed commands are often imitated in other line-based editors. For example, EDLIN
Edlin
Edlin is a line editor included with MS-DOS and later Microsoft operating systems. It provides rudimentary capabilities for editing plain text files through a command-driven interface. Line numbers are specified using numerals, and operations are specified using single-character alphabetic...
in early MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
versions and 32-bit
32-bit
The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295. Hence, a processor with 32-bit memory addresses can directly access 4 GB of byte-addressable memory....
versions of Windows NT
Windows NT
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
has a somewhat similar syntax, and text editors in many MUD
MUD
A MUD , pronounced , is a multiplayer real-time virtual world, with the term usually referring to text-based instances of these. MUDs combine elements of role-playing games, hack and slash, player versus player, interactive fiction, and online chat...
s (LPMud
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...
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
ed is the standard Unix text editor.
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 put 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 (a lone comma is also a synonym for %) 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.
Bill Joy, vi, and ed
In the editor wars, EmacsEmacs
Emacs is a class of text editors, usually characterized by their extensibility. GNU Emacs has over 1,000 commands. It also allows the user to combine these commands into macros to automate work.Development began in the mid-1970s and continues actively...
proponents used to say, "even Bill Joy
Bill Joy
William Nelson Joy , commonly known as Bill Joy, is an American computer scientist. Joy co-founded Sun Microsystems in 1982 along with Vinod Khosla, Scott McNealy and Andy Bechtolsheim, and served as chief scientist at the company until 2003...
doesn't use vi anymore."
In a 1984 interview Bill Joy explained that, at Sun
Sun Microsystems
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
, he used an early desktop publishing program, called Interleaf
Interleaf
Founded in 1981, Interleaf was a company that created software products for the technical publishing creation and distribution process. Its initial product was the first commercial document processor that integrated text and graphics editing, producing WYSIWYG output at near-typeset quality...
;
when visiting labs outside Sun, he used plain old ed. Although vi was almost ubiquitous, he could not count on the local version working the way he expected. However, ed was never modified, so he could rely on a consistent experience.
See also
- EdlinEdlinEdlin is a line editor included with MS-DOS and later Microsoft operating systems. It provides rudimentary capabilities for editing plain text files through a command-driven interface. Line numbers are specified using numerals, and operations are specified using single-character alphabetic...
, the standard MS-DOS line editor. - List of Unix programs
- Editor warEditor warEditor war is the common name for the rivalry between users of the vi and Emacs text editors. The rivalry has become a lasting part of hacker culture and the free software community....
- viVivi is a screen-oriented text editor originally created for the Unix operating system. The portable subset of the behavior of vi and programs based on it, and the ex editor language supported within these programs, is described by the Single Unix Specification and POSIX.The original code for vi...
External links
- Manual page from Unix First Edition describing ed.
- GNU ed homepage
- ed(1) from the Plan 9 from Bell LabsPlan 9 from Bell LabsPlan 9 from Bell Labs is a distributed operating system. It was developed primarily for research purposes as the successor to Unix by the Computing Sciences Research Center at Bell Labs between the mid-1980s and 2002...
manual, a direct descendant of the original ed. - GNU ed for Win32
- Unix Editors I
- Examples for ed in scripts
- ed Humor ("Ed is the standard text editor")