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+.\"	$NetBSD: ed.1,v 1.35 2018/04/09 06:57:01 wiz Exp $
+.\"	$OpenBSD: ed.1,v 1.42 2003/07/27 13:25:43 jmc Exp $
+.\"
+.\" Copyright (c) 1993 Andrew Moore, Talke Studio.
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.Dd April 5, 2018
+.Dt ED 1
+.Os
+.Sh NAME
+.Nm ed
+.Nd text editor
+.Sh SYNOPSIS
+.Nm
+.Op Fl
+.Op Fl ESsx
+.Op Fl p Ar string
+.Op Ar file
+.Sh DESCRIPTION
+.Nm
+is a line-oriented text editor.
+It is used to create, display, modify, and otherwise manipulate text files.
+If invoked with a
+.Ar file
+argument, then a copy of
+.Ar file
+is read into the editor's buffer.
+Changes are made to this copy and not directly to
+.Ar file
+itself.
+Upon quitting
+.Nm ,
+any changes not explicitly saved with a
+.Ic w
+command are lost.
+.Pp
+Editing is done in two distinct modes:
+.Em command
+and
+.Em input .
+When first invoked,
+.Nm
+is in command mode.
+In this mode, commands are read from the standard input and
+executed to manipulate the contents of the editor buffer.
+.Pp
+A typical command might look like:
+.Bd -literal -offset indent
+,s/old/new/g
+.Ed
+.Pp
+which replaces all occurrences of the string
+.Pa old
+with
+.Pa new .
+.Pp
+When an input command, such as
+.Ic a
+(append),
+.Ic i
+(insert),
+or
+.Ic c
+(change) is given,
+.Nm
+enters input mode.
+This is the primary means of adding text to a file.
+In this mode, no commands are available;
+instead, the standard input is written directly to the editor buffer.
+Lines consist of text up to and including a newline character.
+Input mode is terminated by entering a single period
+.Pq Ql \&.
+on a line.
+.Pp
+All
+.Nm
+commands operate on whole lines or ranges of lines; e.g.,
+the
+.Ic d
+command deletes lines; the
+.Ic m
+command moves lines, and so on.
+It is possible to modify only a portion of a line by means of replacement,
+as in the example above.
+However, even here, the
+.Ic s
+command is applied to whole lines at a time.
+.Pp
+In general,
+.Nm
+commands consist of zero or more line addresses, followed by a single
+character command and possibly additional parameters; i.e.,
+commands have the structure:
+.Bd -literal -offset indent
+[address [,address]]command[parameters]
+.Ed
+.Pp
+The address(es) indicate the line or range of lines to be affected by the
+command.
+If fewer addresses are given than the command accepts, then
+default addresses are supplied.
+.Pp
+The options are as follows:
+.Bl -tag -width Ds
+.It Fl
+Same as the
+.Fl s
+option (deprecated).
+.It Fl E
+Enables the use of extended regular expressions instead of the basic
+regular expressions that are normally used.
+.It Fl p Ar string
+Specifies a command prompt.
+This may be toggled on and off with the
+.Ic P
+command.
+.It Fl S
+Disables using of the
+.Ic \&!
+command (executing a subshell).
+Intended to be used by batch jobs like
+.Xr patch 1 .
+.It Fl s
+Suppress diagnostics.
+This should be used if
+.Nm
+standard input is from a script.
+.It Fl x
+Prompt for an encryption key to be used in subsequent reads and writes
+(see the
+.Ic x
+command).
+.It Ar file
+Specifies the name of a file to read.
+If
+.Ar file
+is prefixed with a
+bang
+.Pq Ql \&! ,
+then it is interpreted as a shell command.
+In this case, what is read is the standard output of
+.Ar file
+executed via
+.Xr sh 1 .
+To read a file whose name begins with a bang, prefix the
+name with a backslash
+.Pq Ql \e .
+The default filename is set to
+.Ar file
+only if it is not prefixed with a bang.
+.El
+.Ss LINE ADDRESSING
+An address represents the number of a line in the buffer.
+.Nm
+maintains a
+.Em current address
+which is typically supplied to commands as the default address
+when none is specified.
+When a file is first read, the current address is set to the last line
+of the file.
+In general, the current address is set to the last line affected by a command.
+.Pp
+A line address is
+constructed from one of the bases in the list below, optionally followed
+by a numeric offset.
+The offset may include any combination of digits, operators (i.e.,
+.Sq + ,
+.Sq - ,
+and
+.Sq ^ ) ,
+and whitespace.
+Addresses are read from left to right, and their values are computed
+relative to the current address.
+.Pp
+One exception to the rule that addresses represent line numbers is the
+address
+.Em 0
+(zero).
+This means
+.Dq before the first line ,
+and is legal wherever it makes sense.
+.Pp
+An address range is two addresses separated either by a comma or semi-colon.
+The value of the first address in a range cannot exceed the
+value of the second.
+If only one address is given in a range,
+then the second address is set to the given address.
+If an
+.Em n Ns No -tuple
+of addresses is given where
+.Em n > 2 ,
+then the corresponding range is determined by the last two addresses in the
+.Em n Ns No -tuple.
+If only one address is expected, then the last address is used.
+.Pp
+Each address in a comma-delimited range is interpreted relative to the
+current address.
+In a semi-colon-delimited range, the first address is
+used to set the current address, and the second address is interpreted
+relative to the first.
+.Pp
+The following address symbols are recognized:
+.Bl -tag -width Ds
+.It Em \&.
+The current line (address) in the buffer.
+.It Em $
+The last line in the buffer.
+.It Em n
+The
+.Em n Ns No th
+line in the buffer where
+.Em n
+is a number in the range
+.Em [0,$] .
+.It Em - No or Em ^
+The previous line.
+This is equivalent to
+.Em -1
+and may be repeated with cumulative effect.
+.It Em -n No or Em ^n
+The
+.Em n Ns No th
+previous line, where
+.Em n
+is a non-negative number.
+.It Em +
+The next line.
+This is equivalent to
+.Em +1
+and may be repeated with cumulative effect.
+.It Em +n
+The
+.Em n Ns No th
+next line, where
+.Em n
+is a non-negative number.
+.It Em whitespace Em n
+.Em whitespace
+followed by a number
+.Em n
+is interpreted as
+.Sq Em +n .
+.It Em \&, No or Em %
+The first through last lines in the buffer.
+This is equivalent to the address range
+.Em 1,$ .
+.It Em \&;
+The current through last lines in the buffer.
+This is equivalent to the address range
+.Em .,$ .
+.It Em / Ns Ar re Ns Em /
+The next line containing the regular expression
+.Ar re .
+The search wraps to the beginning of the buffer and continues down to the
+current line, if necessary.
+.Em //
+repeats the last search.
+.It Em \&? Ns Ar re Ns Em \&?
+The previous line containing the regular expression
+.Ar re .
+The search wraps to the end of the buffer and continues up to the
+current line, if necessary.
+.Em ??
+repeats the last search.
+.It Em \&\' Ns Ar lc
+The line previously marked by a
+.Ic k
+(mark) command, where
+.Ar lc
+is a lower case letter.
+.El
+.Ss REGULAR EXPRESSIONS
+Regular expressions are patterns used in selecting text.
+For example, the
+.Nm
+command
+.Bd -literal -offset indent
+g/string/
+.Ed
+.Pp
+prints all lines containing
+.Em string .
+Regular expressions are also used by the
+.Ic s
+command for selecting old text to be replaced with new.
+.Pp
+In addition to specifying string literals, regular expressions can
+represent classes of strings.
+Strings thus represented are said to be matched by the
+corresponding regular expression.
+If it is possible for a regular expression to match several strings in
+a line, then the leftmost longest match is the one selected.
+.Pp
+The following symbols are used in constructing regular expressions:
+.Bl -tag -width Dsasdfsd
+.It Em c
+Any character
+.Em c
+not listed below, including
+.Sq { ,
+.Sq } ,
+.Sq \&( ,
+.Sq \&) ,
+.Sq < ,
+and
+.Sq >
+matches itself.
+.It Em \ec
+Any backslash-escaped character
+.Em c ,
+except for
+.Sq { ,
+.Sq } ,
+.Sq \&( ,
+.Sq \&) ,
+.Sq < ,
+and
+.Sq >
+matches itself.
+.It Em \&.
+Matches any single character.
+.It Em [char-class]
+Matches any single character in the character class
+.Em char-class .
+See
+.Sx CHARACTER CLASSES
+below for further information.
+.It Em [^char-class]
+Matches any single character, other than newline, not in the
+character class
+.Em char-class .
+.It Em ^
+If
+.Em ^
+is the first character of a regular expression, then it
+anchors the regular expression to the beginning of a line.
+Otherwise, it matches itself.
+.It Em $
+If
+.Em $
+is the last character of a regular expression,
+it anchors the regular expression to the end of a line.
+Otherwise, it matches itself.
+.It Em \e<
+Anchors the single character regular expression or subexpression
+immediately following it to the beginning of a word.
+(This may not be available.)
+.It Em \e>
+Anchors the single character regular expression or subexpression
+immediately following it to the end of a word.
+(This may not be available.)
+.It Em \e( Ns Ar re Ns Em \e)
+Defines a subexpression
+.Ar re .
+Subexpressions may be nested.
+A subsequent backreference of the form
+.Em \en ,
+where
+.Em n
+is a number in the range [1,9], expands to the text matched by the
+.Em n Ns No th
+subexpression.
+For example, the regular expression
+.Em \e(.*\e)\e1
+matches any string consisting of identical adjacent substrings.
+Subexpressions are ordered relative to their left delimiter.
+.It Em *
+Matches the single character regular expression or subexpression
+immediately preceding it zero or more times.
+If
+.Em *
+is the first character of a regular expression or subexpression,
+then it matches itself.
+The
+.Em *
+operator sometimes yields unexpected results.
+For example, the regular expression
+.Em b*
+matches the beginning of the string
+.Em abbb
+(as opposed to the substring
+.Em bbb ) ,
+since a null match is the only leftmost match.
+.Sm off
+.It Em \e{ No n,m Em \e}\ \e{ No n, Em \e}\ \& Em \e{ No n Em \e}
+.Sm on
+Matches the single character regular expression or subexpression
+immediately preceding it at least
+.Em n
+and at most
+.Em m
+times.
+If
+.Em m
+is omitted, then it matches at least
+.Em n
+times.
+If the comma is also omitted, then it matches exactly
+.Em n
+times.
+.El
+.Pp
+Additional regular expression operators may be defined depending on the
+particular
+.Xr regex 3
+implementation.
+.Ss CHARACTER CLASSES
+A character class specifies a set of characters.
+It is written within square brackets
+.Pq []
+and in its most basic form contains just the characters in the set.
+.Pp
+To include a
+.Sq \&]
+in a character class, it must be the first character.
+A range of characters may be specified by separating the end characters
+of the range with a
+.Sq \&- ,
+e.g.,
+.Sq a-z
+specifies the lower case characters.
+.Pp
+The following literals can also be used within character classes as
+shorthand for particular sets of characters:
+.Bl -tag -offset indent -compact -width [:blahblah:]
+.It [:alnum:]
+Alphanumeric characters.
+.It [:cntrl:]
+Control characters.
+.It [:lower:]
+Lowercase alphabetic characters.
+.It [:space:]
+Whitespace (space, tab, newline, form feed, etc.)
+.It [:alpha:]
+Alphabetic characters.
+.It [:digit:]
+Numeric characters (digits).
+.It [:print:]
+Printable characters.
+.It [:upper:]
+Uppercase alphabetic characters.
+.It [:blank:]
+Blank characters (space and tab).
+.It [:graph:]
+Graphical characters (printing nonblank characters).
+.It [:punct:]
+Punctuation characters.
+.It [:xdigit:]
+Hexadecimal digits.
+.El
+If
+.Sq \&-
+appears as the first or last character of a character class, then
+it matches itself.
+All other characters in a character class match themselves.
+.Pp
+Patterns in
+a character class
+of the form
+.Em [.col-elm.]
+or
+.Em [=col-elm=]
+where
+.Em col-elm
+is a
+.Em collating element
+are interpreted according to the locale
+.\" .Xr locale 5
+(not currently supported).
+See
+.Xr regex 3
+for an explanation of these constructs.
+.Ss COMMANDS
+All
+.Nm
+commands are single characters, though some require additional parameters.
+If a command's parameters extend over several lines, then
+each line except for the last must be terminated with a backslash
+.Pq Ql \e .
+.Pp
+In general, at most one command is allowed per line.
+However, most commands accept a print suffix, which is any of
+.Ic p
+(print),
+.Ic l
+(list),
+or
+.Ic n
+(enumerate), to print the last line affected by the command.
+.Pp
+An interrupt (typically ^C) has the effect of aborting the current command
+and returning the editor to command mode.
+.Pp
+.Nm
+recognizes the following commands.
+The commands are shown together with
+the default address or address range supplied if none is
+specified (in parentheses), and other possible arguments on the right.
+.Bl -tag -width Dxxs
+.It (.) Ns Ic a
+Appends text to the buffer after the addressed line.
+Text is entered in input mode.
+The current address is set to last line entered.
+.It (.,.) Ns Ic c
+Changes lines in the buffer.
+The addressed lines are deleted from the buffer,
+and text is appended in their place.
+Text is entered in input mode.
+The current address is set to last line entered.
+.It (.,.) Ns Ic d
+Deletes the addressed lines from the buffer.
+If there is a line after the deleted range, then the current address is set
+to this line.
+Otherwise the current address is set to the line before the deleted range.
+.It Ic e Ar file
+Edits
+.Ar file ,
+and sets the default filename.
+If
+.Ar file
+is not specified, then the default filename is used.
+Any lines in the buffer are deleted before the new file is read.
+The current address is set to the last line read.
+.It Ic e Ar !command
+Edits the standard output of
+.Ar command ,
+(see
+.Ic \&! Ar command
+below).
+The default filename is unchanged.
+Any lines in the buffer are deleted before the output of
+.Em command
+is read.
+The current address is set to the last line read.
+.It Ic E Ar file
+Edits
+.Ar file
+unconditionally.
+This is similar to the
+.Ic e
+command, except that unwritten changes are discarded without warning.
+The current address is set to the last line read.
+.It Ic f Ar file
+Sets the default filename to
+.Ar file .
+If
+.Ar file
+is not specified, then the default unescaped filename is printed.
+.It (1,$) Ns Ic g Ns Ar /re/command-list
+Applies
+.Ar command-list
+to each of the addressed lines matching a regular expression
+.Ar re .
+The current address is set to the line currently matched before
+.Ar command-list
+is executed.
+At the end of the
+.Ic g
+command, the current address is set to the last line affected by
+.Ar command-list .
+.Pp
+Each command in
+.Ar command-list
+must be on a separate line,
+and every line except for the last must be terminated by a backslash
+.Pq Sq \e .
+Any commands are allowed, except for
+.Ic g ,
+.Ic G ,
+.Ic v ,
+and
+.Ic V .
+A newline alone in
+.Ar command-list
+is equivalent to a
+.Ic p
+command.
+.It (1,$) Ns Ic G Ns Ar /re/
+Interactively edits the addressed lines matching a regular expression
+.Ar re .
+For each matching line, the line is printed, the current address is set,
+and the user is prompted to enter a
+.Ar command-list .
+At the end of the
+.Ic G
+command, the current address is set to the last line affected by (the last)
+.Ar command-list .
+.Pp
+The format of
+.Ar command-list
+is the same as that of the
+.Ic g
+command.
+A newline alone acts as a null command list.
+A single
+.Sq &
+repeats the last non-null command list.
+.It Ic H
+Toggles the printing of error explanations.
+By default, explanations are not printed.
+It is recommended that
+.Nm
+scripts begin with this command to aid in debugging.
+.It Ic h
+Prints an explanation of the last error.
+.It (.) Ns Ic i
+Inserts text in the buffer before the current line.
+Text is entered in input mode.
+The current address is set to the last line entered.
+.It (.,.+1) Ns Ic j
+Joins the addressed lines.
+The addressed lines are deleted from the buffer and replaced by a single
+line containing their joined text.
+The current address is set to the resultant line.
+.It (.) Ns Ic k Ns Ar lc
+Marks a line with a lower case letter
+.Ar lc .
+The line can then be addressed as
+.Ar \&'lc
+(i.e., a single quote followed by
+.Ar lc )
+in subsequent commands.
+The mark is not cleared until the line is deleted or otherwise modified.
+.It (.,.) Ns Ic l
+Prints the addressed lines unambiguously.
+If a single line fills more than one screen (as might be the case
+when viewing a binary file, for instance), a
+.Dq --More--
+prompt is printed on the last line.
+.Nm
+waits until the RETURN key is pressed before displaying the next screen.
+The current address is set to the last line printed.
+.It (.,.) Ns Ic m Ns No (.)
+Moves lines in the buffer.
+The addressed lines are moved to after the
+right-hand destination address, which may be the address
+.Em 0
+(zero).
+The current address is set to the last line moved.
+.It (.,.) Ns Ic n
+Prints the addressed lines along with their line numbers.
+The current address is set to the last line printed.
+.It (.,.) Ns Ic p
+Prints the addressed lines.
+The current address is set to the last line printed.
+.It Ic P
+Toggles the command prompt on and off.
+Unless a prompt was specified with the command-line option
+.Fl p Ar string ,
+the command prompt is by default turned off.
+.It Ic q
+Quits
+.Nm .
+.It Ic Q
+Quits
+.Nm
+unconditionally.
+This is similar to the
+.Ic q
+command, except that unwritten changes are discarded without warning.
+.It ($) Ns Ic r Ar file
+Reads
+.Ar file
+to after the addressed line.
+If
+.Ar file
+is not specified, then the default filename is used.
+If there was no default filename prior to the command,
+then the default filename is set to
+.Ar file .
+Otherwise, the default filename is unchanged.
+The current address is set to the last line read.
+.It ($) Ns Ic r Ar !command
+Reads to after the addressed line the standard output of
+.Ar command ,
+(see the
+.Ic \&!
+command below).
+The default filename is unchanged.
+The current address is set to the last line read.
+.Sm off
+.It (.,.) Ic s Ar /re/replacement/ , \ (.,.) \
+Ic s Ar /re/replacement/ Em g , Ar \ (.,.) \
+Ic s Ar /re/replacement/ Em n
+.Sm on
+Replaces text in the addressed lines matching a regular expression
+.Ar re
+with
+.Ar replacement .
+By default, only the first match in each line is replaced.
+If the
+.Em g
+(global) suffix is given, then every match to be replaced.
+The
+.Em n
+suffix, where
+.Em n
+is a positive number, causes only the
+.Em n Ns No th
+match to be replaced.
+It is an error if no substitutions are performed on any of the addressed
+lines.
+The current address is set the last line affected.
+.Pp
+.Ar re
+and
+.Ar replacement
+may be delimited by any character other than space and newline
+(see the
+.Ic s
+command below).
+If one or two of the last delimiters is omitted, then the last line
+affected is printed as though the print suffix
+.Em p
+were specified.
+.Pp
+An unescaped
+.Ql &
+in
+.Ar replacement
+is replaced by the currently matched text.
+The character sequence
+.Em \em ,
+where
+.Em m
+is a number in the range [1,9], is replaced by the
+.Em m Ns No th
+backreference expression of the matched text.
+If
+.Ar replacement
+consists of a single
+.Ql % ,
+then
+.Ar replacement
+from the last substitution is used.
+Newlines may be embedded in
+.Ar replacement
+if they are escaped with a backslash
+.Pq Ql \e .
+.It (.,.) Ns Ic s
+Repeats the last substitution.
+This form of the
+.Ic s
+command accepts a count suffix
+.Em n ,
+or any combination of the characters
+.Em r ,
+.Em g ,
+and
+.Em p .
+If a count suffix
+.Em n
+is given, then only the
+.Em n Ns No th
+match is replaced.
+The
+.Em r
+suffix causes
+the regular expression of the last search to be used instead of
+that of the last substitution.
+The
+.Em g
+suffix toggles the global suffix of the last substitution.
+The
+.Em p
+suffix toggles the print suffix of the last substitution.
+The current address is set to the last line affected.
+.It (.,.) Ns Ic t Ns No (.)
+Copies (i.e., transfers) the addressed lines to after the right-hand
+destination address, which may be the address
+.Em 0
+(zero).
+The current address is set to the last line copied.
+.It Ic u
+Undoes the last command and restores the current address
+to what it was before the command.
+The global commands
+.Ic g ,
+.Ic G ,
+.Ic v ,
+and
+.Ic V
+are treated as a single command by undo.
+.Ic u
+is its own inverse.
+.It (1,$) Ns Ic v Ns Ar /re/command-list
+Applies
+.Ar command-list
+to each of the addressed lines not matching a regular expression
+.Ar re .
+This is similar to the
+.Ic g
+command.
+.It (1,$) Ns Ic V Ns Ar /re/
+Interactively edits the addressed lines not matching a regular expression
+.Ar re .
+This is similar to the
+.Ic G
+command.
+.It (1,$) Ns Ic w Ar file
+Writes the addressed lines to
+.Ar file .
+Any previous contents of
+.Ar file
+are lost without warning.
+If there is no default filename, then the default filename is set to
+.Ar file ,
+otherwise it is unchanged.
+If no filename is specified, then the default filename is used.
+The current address is unchanged.
+.It (1,$) Ns Ic wq Ar file
+Writes the addressed lines to
+.Ar file ,
+and then executes a
+.Ic q
+command.
+.It (1,$) Ns Ic w Ar !command
+Writes the addressed lines to the standard input of
+.Ar command ,
+(see the
+.Ic \&!
+command below).
+The default filename and current address are unchanged.
+.It (1,$) Ns Ic W Ar file
+Appends the addressed lines to the end of
+.Ar file .
+This is similar to the
+.Ic w
+command, except that the previous contents of file are not clobbered.
+The current address is unchanged.
+.It Ic x
+Prompts for an encryption key which is used in subsequent reads and writes.
+If a newline alone is entered as the key, then encryption is turned off.
+Otherwise, echoing is disabled while a key is read.
+Encryption/decryption is done using the
+.Xr bdes 1
+algorithm.
+.It (.+1) Ns Ic z Ns Ar n
+Scrolls
+.Ar n
+lines at a time starting at addressed line.
+If
+.Ar n
+is not specified, then the current window size is used.
+The current address is set to the last line printed.
+.It ($) Ns Ic =
+Prints the line number of the addressed line.
+.It (.+1) Ns Ic newline
+Prints the addressed line, and sets the current address to that line.
+.It Ic \&! Ns Ar command
+Executes
+.Ar command
+via
+.Xr sh 1 .
+If the first character of
+.Ar command
+is
+.Ic \&! ,
+then it is replaced by text of the previous
+.Ic !command .
+.Nm
+does not process
+.Ar command
+for
+.Sq \e
+(backslash) escapes.
+However, an unescaped
+.Sq %
+is replaced by the default filename.
+When the shell returns from execution, a
+.Sq \&!
+is printed to the standard output.
+The current line is unchanged.
+.El
+.Sh LIMITATIONS
+.Nm
+processes
+.Em file
+arguments for backslash escapes, i.e., in a filename,
+any characters preceded by a backslash
+.Pq Ql \e
+are interpreted literally.
+.Pp
+If a text (non-binary) file is not terminated by a newline character,
+then
+.Nm
+appends one on reading/writing it.
+In the case of a binary file,
+.Nm
+does not append a newline on reading/writing.
+.Sh ENVIRONMENT
+.Bl -tag -width iTMPDIR
+.It Ev TMPDIR
+The location used to store temporary files.
+.El
+.Sh FILES
+.Bl -tag -width /tmp/ed.* -compact
+.It Pa /tmp/ed.*
+buffer file
+.It Pa ed.hup
+where
+.Nm
+attempts to write the buffer if the terminal hangs up
+.El
+.Sh DIAGNOSTICS
+When an error occurs,
+.Nm
+prints a
+.Dq \&?
+and either returns to command mode or exits if its input is from a script.
+An explanation of the last error can be printed with the
+.Ic h
+(help) command.
+.Pp
+Since the
+.Ic g
+(global) command masks any errors from failed searches and substitutions,
+it can be used to perform conditional operations in scripts; e.g.,
+.Bd -literal -offset indent
+g/old/s//new/
+.Ed
+.Pp
+replaces any occurrences of
+.Em old
+with
+.Em new .
+.Pp
+If the
+.Ic u
+(undo) command occurs in a global command list, then
+the command list is executed only once.
+.Pp
+If diagnostics are not disabled, attempting to quit
+.Nm
+or edit another file before writing a modified buffer results in an error.
+If the command is entered a second time, it succeeds,
+but any changes to the buffer are lost.
+.Sh SEE ALSO
+.Xr bdes 1 ,
+.Xr patch 1 ,
+.Xr sed 1 ,
+.Xr sh 1 ,
+.Xr vi 1 ,
+.Xr regex 3
+.Pp
+USD:09-10
+.Rs
+.%A B. W. Kernighan
+.%A P. J. Plauger
+.%B Software Tools in Pascal
+.%I Addison-Wesley
+.%D 1981
+.Re
+.Sh HISTORY
+An
+.Nm
+command appeared in
+.At v1 .