.\" Copyright (c) 1992, 1993
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.\" This code is derived from software contributed to Berkeley by
.\" the Institute of Electrical and Electronics Engineers, Inc.
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\"    notice, this list of conditions and the following disclaimer in the
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.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\"	@(#)sed.1	8.2 (Berkeley) 12/30/93
.\" $FreeBSD$
.\"
.Dd June 10, 2020
.Dt SED 1
.Os
.Sh NAME
.Nm sed
.Nd stream editor
.Sh SYNOPSIS
.Nm
.Op Fl Ealnru
.Ar command
.Op Fl I Ar extension
.Op Fl i Ar extension
.Op Ar
.Nm
.Op Fl Ealnru
.Op Fl e Ar command
.Op Fl f Ar command_file
.Op Fl I Ar extension
.Op Fl i Ar extension
.Op Ar
.Sh DESCRIPTION
The
.Nm
utility reads the specified files, or the standard input if no files
are specified, modifying the input as specified by a list of commands.
The input is then written to the standard output.
.Pp
A single command may be specified as the first argument to
.Nm .
Multiple commands may be specified by using the
.Fl e
or
.Fl f
options.
All commands are applied to the input in the order they are specified
regardless of their origin.
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl E
Interpret regular expressions as extended (modern) regular expressions
rather than basic regular expressions (BRE's).
The
.Xr re_format 7
manual page fully describes both formats.
.It Fl a
The files listed as parameters for the
.Dq w
functions are created (or truncated) before any processing begins,
by default.
The
.Fl a
option causes
.Nm
to delay opening each file until a command containing the related
.Dq w
function is applied to a line of input.
.It Fl e Ar command
Append the editing commands specified by the
.Ar command
argument
to the list of commands.
.It Fl f Ar command_file
Append the editing commands found in the file
.Ar command_file
to the list of commands.
The editing commands should each be listed on a separate line.
The commands are read from the standard input if
.Ar command_file
is
.Dq Li - .
.It Fl I Ar extension
Edit files in-place, saving backups with the specified
.Ar extension .
If a zero-length
.Ar extension
is given, no backup will be saved.
It is not recommended to give a zero-length
.Ar extension
when in-place editing files, as you risk corruption or partial content
in situations where disk space is exhausted, etc.
.Pp
Note that in-place editing with
.Fl I
still takes place in a single continuous line address space covering
all files, although each file preserves its individuality instead of
forming one output stream.
The line counter is never reset between files, address ranges can span
file boundaries, and the
.Dq $
address matches only the last line of the last file.
(See
.Sx "Sed Addresses" . )
That can lead to unexpected results in many cases of in-place editing,
where using
.Fl i
is desired.
.It Fl i Ar extension
Edit files in-place similarly to
.Fl I ,
but treat each file independently from other files.
In particular, line numbers in each file start at 1,
the
.Dq $
address matches the last line of the current file,
and address ranges are limited to the current file.
(See
.Sx "Sed Addresses" . )
The net result is as though each file were edited by a separate
.Nm
instance.
.It Fl l
Make output line buffered.
.It Fl n
By default, each line of input is echoed to the standard output after
all of the commands have been applied to it.
The
.Fl n
option suppresses this behavior.
.It Fl r
Same as
.Fl E
for compatibility with GNU sed.
.It Fl u
Make output unbuffered.
.El
.Pp
The form of a
.Nm
command is as follows:
.Pp
.Dl [address[,address]]function[arguments]
.Pp
Whitespace may be inserted before the first address and the function
portions of the command.
.Pp
Normally,
.Nm
cyclically copies a line of input, not including its terminating newline
character, into a
.Em "pattern space" ,
(unless there is something left after a
.Dq D
function),
applies all of the commands with addresses that select that pattern space,
copies the pattern space to the standard output, appending a newline, and
deletes the pattern space.
.Pp
Some of the functions use a
.Em "hold space"
to save all or part of the pattern space for subsequent retrieval.
.Sh "Sed Addresses"
An address is not required, but if specified must have one of the
following formats:
.Bl -bullet -offset indent
.It
a number that counts
input lines
cumulatively across input files (or in each file independently
if a
.Fl i
option is in effect);
.It
a dollar
.Pq Dq $
character that addresses the last line of input (or the last line
of the current file if a
.Fl i
option was specified);
.It
a context address
that consists of a regular expression preceded and followed by a
delimiter.
The closing delimiter can also optionally be followed by the
.Dq I
character, to indicate that the regular expression is to be matched
in a case-insensitive way.
.El
.Pp
A command line with no addresses selects every pattern space.
.Pp
A command line with one address selects all of the pattern spaces
that match the address.
.Pp
A command line with two addresses selects an inclusive range.
This
range starts with the first pattern space that matches the first
address.
The end of the range is the next following pattern space
that matches the second address.
If the second address is a number
less than or equal to the line number first selected, only that
line is selected.
The number in the second address may be prefixed with a
.Pq Dq \&+
to specify the number of lines to match after the first pattern.
In the case when the second address is a context
address,
.Nm
does not re-match the second address against the
pattern space that matched the first address.
Starting at the
first line following the selected range,
.Nm
starts looking again for the first address.
.Pp
Editing commands can be applied to non-selected pattern spaces by use
of the exclamation character
.Pq Dq \&!
function.
.Sh "Sed Regular Expressions"
The regular expressions used in
.Nm ,
by default, are basic regular expressions (BREs, see
.Xr re_format 7
for more information), but extended (modern) regular expressions can be used
instead if the
.Fl E
flag is given.
In addition,
.Nm
has the following two additions to regular expressions:
.Pp
.Bl -enum -compact
.It
In a context address, any character other than a backslash
.Pq Dq \e
or newline character may be used to delimit the regular expression.
The opening delimiter needs to be preceded by a backslash
unless it is a slash.
For example, the context address
.Li \exabcx
is equivalent to
.Li /abc/ .
Also, putting a backslash character before the delimiting character
within the regular expression causes the character to be treated literally.
For example, in the context address
.Li \exabc\exdefx ,
the RE delimiter is an
.Dq x
and the second
.Dq x
stands for itself, so that the regular expression is
.Dq abcxdef .
.Pp
.It
The escape sequence \en matches a newline character embedded in the
pattern space.
You cannot, however, use a literal newline character in an address or
in the substitute command.
.El
.Pp
One special feature of
.Nm
regular expressions is that they can default to the last regular
expression used.
If a regular expression is empty, i.e., just the delimiter characters
are specified, the last regular expression encountered is used instead.
The last regular expression is defined as the last regular expression
used as part of an address or substitute command, and at run-time, not
compile-time.
For example, the command
.Dq /abc/s//XXX/
will substitute
.Dq XXX
for the pattern
.Dq abc .
.Sh "Sed Functions"
In the following list of commands, the maximum number of permissible
addresses for each command is indicated by [0addr], [1addr], or [2addr],
representing zero, one, or two addresses.
.Pp
The argument
.Em text
consists of one or more lines.
To embed a newline in the text, precede it with a backslash.
Other backslashes in text are deleted and the following character
taken literally.
.Pp
The
.Dq r
and
.Dq w
functions take an optional file parameter, which should be separated
from the function letter by white space.
Each file given as an argument to
.Nm
is created (or its contents truncated) before any input processing begins.
.Pp
The
.Dq b ,
.Dq r ,
.Dq s ,
.Dq t ,
.Dq w ,
.Dq y ,
.Dq \&! ,
and
.Dq \&:
functions all accept additional arguments.
The following synopses indicate which arguments have to be separated from
the function letters by white space characters.
.Pp
Two of the functions take a function-list.
This is a list of
.Nm
functions separated by newlines, as follows:
.Bd -literal -offset indent
{ function
  function
  ...
  function
}
.Ed
.Pp
The
.Dq {
can be preceded by white space and can be followed by white space.
The function can be preceded by white space.
The terminating
.Dq }
must be preceded by a newline, and may also be preceded by white space.
.Pp
.Bl -tag -width "XXXXXX" -compact
.It [2addr] function-list
Execute function-list only when the pattern space is selected.
.Pp
.It [1addr]a\e
.It text
Write
.Em text
to standard output immediately before each attempt to read a line of input,
whether by executing the
.Dq N
function or by beginning a new cycle.
.Pp
.It [2addr]b[label]
Branch to the
.Dq \&:
function with the specified label.
If the label is not specified, branch to the end of the script.
.Pp
.It [2addr]c\e
.It text
Delete the pattern space.
With 0 or 1 address or at the end of a 2-address range,
.Em text
is written to the standard output.
.Pp
.It [2addr]d
Delete the pattern space and start the next cycle.
.Pp
.It [2addr]D
Delete the initial segment of the pattern space through the first
newline character and start the next cycle.
.Pp
.It [2addr]g
Replace the contents of the pattern space with the contents of the
hold space.
.Pp
.It [2addr]G
Append a newline character followed by the contents of the hold space
to the pattern space.
.Pp
.It [2addr]h
Replace the contents of the hold space with the contents of the
pattern space.
.Pp
.It [2addr]H
Append a newline character followed by the contents of the pattern space
to the hold space.
.Pp
.It [1addr]i\e
.It text
Write
.Em text
to the standard output.
.Pp
.It [2addr]l
(The letter ell.)
Write the pattern space to the standard output in a visually unambiguous
form.
This form is as follows:
.Pp
.Bl -tag -width "carriage-returnXX" -offset indent -compact
.It backslash
\e\e
.It alert
\ea
.It form-feed
\ef
.It carriage-return
\er
.It tab
\et
.It vertical tab
\ev
.El
.Pp
Nonprintable characters are written as three-digit octal numbers (with a
preceding backslash) for each byte in the character (most significant byte
first).
Long lines are folded, with the point of folding indicated by displaying
a backslash followed by a newline.
The end of each line is marked with a
.Dq $ .
.Pp
.It [2addr]n
Write the pattern space to the standard output if the default output has
not been suppressed, and replace the pattern space with the next line of
input.
.Pp
.It [2addr]N
Append the next line of input to the pattern space, using an embedded
newline character to separate the appended material from the original
contents.
Note that the current line number changes.
.Pp
.It [2addr]p
Write the pattern space to standard output.
.Pp
.It [2addr]P
Write the pattern space, up to the first newline character to the
standard output.
.Pp
.It [1addr]q
Branch to the end of the script and quit without starting a new cycle.
.Pp
.It [1addr]r file
Copy the contents of
.Em file
to the standard output immediately before the next attempt to read a
line of input.
If
.Em file
cannot be read for any reason, it is silently ignored and no error
condition is set.
.Pp
.It [2addr]s/regular expression/replacement/flags
Substitute the replacement string for the first instance of the regular
expression in the pattern space.
Any character other than backslash or newline can be used instead of
a slash to delimit the RE and the replacement.
Within the RE and the replacement, the RE delimiter itself can be used as
a literal character if it is preceded by a backslash.
.Pp
An ampersand
.Pq Dq &
appearing in the replacement is replaced by the string matching the RE.
The special meaning of
.Dq &
in this context can be suppressed by preceding it by a backslash.
The string
.Dq \e# ,
where
.Dq #
is a digit, is replaced by the text matched
by the corresponding backreference expression (see
.Xr re_format 7 ) .
.Pp
A line can be split by substituting a newline character into it.
To specify a newline character in the replacement string, precede it with
a backslash.
.Pp
The value of
.Em flags
in the substitute function is zero or more of the following:
.Bl -tag -width "XXXXXX" -offset indent
.It Ar N
Make the substitution only for the
.Ar N Ns 'th
occurrence of the regular expression in the pattern space.
.It g
Make the substitution for all non-overlapping matches of the
regular expression, not just the first one.
.It p
Write the pattern space to standard output if a replacement was made.
If the replacement string is identical to that which it replaces, it
is still considered to have been a replacement.
.It w Em file
Append the pattern space to
.Em file
if a replacement was made.
If the replacement string is identical to that which it replaces, it
is still considered to have been a replacement.
.It i or I
Match the regular expression in a case-insensitive way.
.El
.Pp
.It [2addr]t [label]
Branch to the
.Dq \&:
function bearing the label if any substitutions have been made since the
most recent reading of an input line or execution of a
.Dq t
function.
If no label is specified, branch to the end of the script.
.Pp
.It [2addr]w Em file
Append the pattern space to the
.Em file .
.Pp
.It [2addr]x
Swap the contents of the pattern and hold spaces.
.Pp
.It [2addr]y/string1/string2/
Replace all occurrences of characters in
.Em string1
in the pattern space with the corresponding characters from
.Em string2 .
Any character other than a backslash or newline can be used instead of
a slash to delimit the strings.
Within
.Em string1
and
.Em string2 ,
a backslash followed by any character other than a newline is that literal
character, and a backslash followed by an ``n'' is replaced by a newline
character.
.Pp
.It [2addr]!function
.It [2addr]!function-list
Apply the function or function-list only to the lines that are
.Em not
selected by the address(es).
.Pp
.It [0addr]:label
This function does nothing; it bears a label to which the
.Dq b
and
.Dq t
commands may branch.
.Pp
.It [1addr]=
Write the line number to the standard output followed by a newline
character.
.Pp
.It [0addr]
Empty lines are ignored.
.Pp
.It [0addr]#
The
.Dq #
and the remainder of the line are ignored (treated as a comment), with
the single exception that if the first two characters in the file are
.Dq #n ,
the default output is suppressed.
This is the same as specifying the
.Fl n
option on the command line.
.El
.Sh ENVIRONMENT
The
.Ev COLUMNS , LANG , LC_ALL , LC_CTYPE
and
.Ev LC_COLLATE
environment variables affect the execution of
.Nm
as described in
.Xr environ 7 .
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
Replace
.Ql bar
with
.Ql baz
when piped from another command:
.Bd -literal -offset indent
echo "An alternate word, like bar, is sometimes used in examples." | sed 's/bar/baz/'
.Ed
.Pp
Using backlashes can sometimes be hard to read and follow:
.Bd -literal -offset indent
echo "/home/example" | sed  's/\\/home\\/example/\\/usr\\/local\\/example/'
.Ed
.Pp
Using a different separator can be handy when working with paths:
.Bd -literal -offset indent
echo "/home/example" | sed 's#/home/example#/usr/local/example#'
.Ed
.Pp
Replace all occurances of
.Ql foo
with
.Ql bar
in the file
.Pa test.txt ,
without creating a backup of the file:
.Bd -literal -offset indent
sed -i '' -e 's/foo/bar/g' test.txt
.Ed
.Sh SEE ALSO
.Xr awk 1 ,
.Xr ed 1 ,
.Xr grep 1 ,
.Xr regex 3 ,
.Xr re_format 7
.Sh STANDARDS
The
.Nm
utility is expected to be a superset of the
.St -p1003.2
specification.
.Pp
The
.Fl E , I , a
and
.Fl i
options, the special meaning of
.Fl f Cm - ,
the prefixing
.Dq \&+
in the second member of an address range,
as well as the
.Dq I
flag to the address regular expression and substitution command are
non-standard
.Fx
extensions and may not be available on other operating systems.
.Sh HISTORY
A
.Nm
command, written by
.An L. E. McMahon ,
appeared in
.At v7 .
.Sh AUTHORS
.An Diomidis D. Spinellis Aq Mt dds@FreeBSD.org
.Sh BUGS
Multibyte characters containing a byte with value 0x5C
.Tn ( ASCII
.Ql \e )
may be incorrectly treated as line continuation characters in arguments to the
.Dq a ,
.Dq c
and
.Dq i
commands.
Multibyte characters cannot be used as delimiters with the
.Dq s
and
.Dq y
commands.