Original author(s) | Ken Thompson |
---|---|
Developer(s) | AT&T Bell Laboratories |
Initial release | 1973, 50–51 years ago |
Written in | C |
Operating system | Unix, Unix-like, Plan 9 |
Platform | Cross-platform |
Type | Text editor |
License | Plan 9: MIT License |
ed (pronounced as distinct letters, /ˌiːˈdiː/ ) [1] is a line editor for Unix and Unix-like operating systems. It was one of the first parts of the Unix operating system that was developed, in August 1969. [2] It remains part of the POSIX and Open Group standards for Unix-based operating systems, [3] alongside the more sophisticated full-screen editor vi.
The ed text editor was one of the first three key elements of the Unix operating system—assembler, editor, and shell—developed by Ken Thompson in August 1969 on a PDP-7 at AT&T Bell Labs. [2] Many features of ed came from the qed text editor developed at Thompson's alma mater University of California, Berkeley. [4] Thompson was very familiar with qed, and had reimplemented it on the CTSS and Multics systems. Thompson's versions of qed were notable as the first to implement regular expressions. 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, [5] and aspects of ed went on to influence ex, which in turn spawned vi. The non-interactive Unix command grep was inspired by a common special use of qed and later ed, where the command g/re/p
performs a global regular expression search and prints the lines containing matches. The Unix stream editor, sed implemented many of the scripting features of qed that were not supported by ed on Unix. [6] [ failed verification ] [7]
Features of ed include:
(In)famous for its terseness, ed, compatible with teletype terminals like Teletype Model 33, gives almost no visual feedback, [8] and has been called (by Peter H. Salus) "the most user-hostile editor ever created", even when compared to the contemporary (and notoriously complex) TECO. [2] 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. [8] This terseness was appropriate in the early versions of Unix, when consoles were teletypes, modems were slow, and memory 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 scripts. 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. 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. [9] 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 has a few switches to enhance the feedback. Using ed -v -p:
provides a simple prompt and enables more useful feedback messages. [10] The -p
switch is defined in POSIX since XPG2 (1987). [3]
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 MUDs (LPMud and descendants, for example) use ed-like syntax. These editors, however, are typically more limited in function.
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.$$This is line number two.$ w text.txt 633s/two/three/
,l ed is the standard Unix text editor.$$This is line number three.$ w text.txt 65 q
The end result is a simple text file text.txt
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.txt
writes the buffer to the file text.txt
making ed respond with 65, the number of characters written to the file. q
will end an ed session.
The GNU Project has numerous jokes around ed hosted on its website. In addition, the glibc documentation notes an error code called ED
with its description (errorstr) merely a single question mark, noting "the experienced user will know what is wrong." [11]
AWK is a domain-specific language designed for text processing and typically used as a data extraction and reporting tool. Like sed and grep, it is a filter, and is a standard feature of most Unix-like operating systems.
Edlin is a line editor, and the only text editor provided with early versions of IBM PC DOS, MS-DOS and OS/2. Although superseded in MS-DOS 5.0 and later by the full-screen MS-DOS Editor, and by Notepad in Microsoft Windows, it continues to be included in the 32-bit versions of current Microsoft operating systems.
sed is a Unix utility that parses and transforms text, using a simple, compact programming language. It was developed from 1973 to 1974 by Lee E. McMahon of Bell Labs, and is available today for most operating systems. sed was based on the scripting features of the interactive editor ed and the earlier qed. It was one of the earliest tools to support regular expressions, and remains in use for text processing, most notably with the substitution command. Popular alternative tools for plaintext string manipulation and "stream editing" include AWK and Perl.
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.
grep
is a command-line utility for searching plaintext datasets for lines that match a regular expression. Its name comes from the ed command g/re/p
, which has the same effect. grep
was originally developed for the Unix operating system, but later available for all Unix-like systems and some others such as OS-9.
uniq
is a utility command on Unix, Plan 9, Inferno, and Unix-like operating systems which, when fed a text file or standard input, outputs the text with adjacent identical lines collapsed to one, unique line of text.
In software development, Make is a command-line interface software tool that performs actions ordered by configured dependencies as defined in a configuration file called a makefile. It is commonly used for build automation to build executable code from source code. But, not limited to building, Make can perform any operation available via the operating system shell.
A newline is a control character or sequence of control characters in character encoding specifications such as ASCII, EBCDIC, Unicode, etc. This character, or a sequence of characters, is used to signify the end of a line of text and the start of a new one.
xargs is a command on Unix and most Unix-like operating systems used to build and execute commands from standard input. It converts input from standard input into arguments to a command.
wc
is a command in Unix, Plan 9, Inferno, and Unix-like operating systems. The program reads either standard input or a list of computer files and generates one or more of the following statistics: newline count, word count, and byte count. If a list of files is provided, both individual file and total statistics follow.
nl is a Unix utility for numbering lines, either from a file or from standard input, reproducing output on standard output.
In Unix-like computer operating systems, a pipeline is a mechanism for inter-process communication using message passing. A pipeline is a set of processes chained together by their standard streams, so that the output text of each process (stdout) is passed directly as input (stdin) to the next one. The second process is started as the first process is still executing, and they are executed concurrently.
In Unix-like operating systems, find
is a command-line utility that locates files based on some user-specified criteria and either prints the pathname of each matched object or, if another action is requested, performs that action on each matched object.
In computing, tee
is a command in command-line interpreters (shells) using standard streams which reads standard input and writes it to both standard output and one or more files, effectively duplicating its input. It is primarily used in conjunction with pipes and filters. The command is named after the T-splitter used in plumbing.
In computing, sort is a standard command line program of Unix and Unix-like operating systems, that prints the lines of its input or concatenation of all files listed in its argument list in sorted order. Sorting is done based on one or more sort keys extracted from each line of input. By default, the entire input is taken as sort key. Blank space is the default field separator. The command supports a number of command-line options that can vary by implementation. For instance the "-r
" flag will reverse the sort order.
In Unix and Unix-like operating systems, job control refers to control of jobs by a shell, especially interactively, where a "job" is a shell's representation for a process group. Basic job control features are the suspending, resuming, or terminating of all processes in the job/process group; more advanced features can be performed by sending signals to the job. Job control is of particular interest in Unix due to its multiprocessing, and should be distinguished from job control generally, which is frequently applied to sequential execution.
GNU Emacs is a free software tool and text editor that also features web browsers, a file manager, note-taking software, multiple IRC clients, and more. It was created by GNU Project founder Richard Stallman, based on the Emacs editor developed for Unix operating systems. GNU Emacs has been a central component of the GNU project and a flagship project of the free software movement.
Emacs, originally named EMACS, 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, self-documenting, real-time display editor". Development of the first Emacs began in the mid-1970s, and work on GNU Emacs, directly descended from the original, is ongoing; its latest version is 29.4, released June 2024.
Unix is a family of multitasking, multi-user 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 others.
cat
is a standard Unix utility that reads files sequentially, writing them to standard output. The name is derived from its function to (con)catenate files . It has been ported to a number of operating systems.
A while later a demand arose for another special-purpose program, gres, for substitution: g/re/s. Lee McMahon undertook to write it, and soon foresaw that there would be no end to the family: g/re/d, g/re/a, etc. As his concept developed it became sed…