sed scripts consist of editing commands, one per line, of the following form:

[ address [, address ] ] function [ arguments ]

In normal operation, sed cyclically copies a line of input into a pattern space (unless there is something left after a D command), sequentially applies all commands with addresses matching that pattern space until reaching the end of the script, copies the pattern space to the standard output (except under -n), and finally, deletes the pattern space.

Some commands use a hold space to save all or part of the pattern space for subsequent retrieval.

An address is either:

• a decimal number linecount, which is cumulative across input files;
• a $, which addresses the last input line;
• or a context address, which is a /regular expression/ as described on the regexp(5) manual page, with the following exceptions:

  \?RE?

  In a context address, the construction \?regular expression?, where ? is any character, is identical to /regular expression/. Note: in the context address \xabc\xdefx, the second x stands for itself, so that the regular expression is abcxdef.

  \n

  Matches a NEWLINE embedded in the pattern space.

  .

  Matches any character except the NEWLINE ending the pattern space.

  null

  A command line with no address selects every pattern space.

  address

  Selects each pattern space that matches.

  address1 ,address2

  Selects the inclusive range from the first pattern space matching address1 to the first pattern space matching address2. Selects only one line if address1 is greater than or equal to address2.

If the first nonwhite character in a line is a `#' (pound sign), sed treats that line as a comment, and ignores it. If, however, the first such line is of the form:

#n

sed runs as if the -n flag were specified.

The maximum number of permissible addresses for each function is indicated in parentheses in the list below.

An argument denoted text consists of one or more lines, all but the last of which end with \ to hide the NEWLINE. Backslashes in text are treated like backslashes in the replacement string of an s command, and may be used to protect initial SPACE and TAB characters against the stripping that is done on every script line.

An argument denoted rfilename or wfilename must terminate the command line and must be preceded by exactly one SPACE. Each wfilename is created before processing begins. There can be at most 10 distinct wfilename arguments.

(1)a\

text

Append: place text on the output before reading the next input line.

(2)b label

Branch to the `:' command bearing the label. Branch to the end of the script if label is empty.

(2)c\

text

Change: delete the pattern space. With 0 or 1 address or at the end of a 2 address range, place text on the output. Start the next cycle.

(2)d

Delete the pattern space. Start the next cycle.

(2)D

Delete the initial segment of the pattern space through the first NEWLINE. Start the next cycle.

(2)g

Replace the contents of the pattern space by the contents of the hold space.

(2)G

Append the contents of the hold space to the pattern space.

(2)h

Replace the contents of the hold space by the contents of the pattern space.

(2)H

Append the contents of the pattern space to the hold space.

(1)i\

text

Insert: place text on the standard output.

(2)l

List the pattern space on the standard output in an unambiguous form. Non-printing characters are spelled in two digit ASCII and long lines are folded.

(2)n

Copy the pattern space to the standard output. Replace the pattern space with the next line of input.

(2)N

Append the next line of input to the pattern space with an embedded newline. (The current line number changes.)

(2)p

Print: copy the pattern space to the standard output.

(2)P

Copy the initial segment of the pattern space through the first NEWLINE to the standard output.

(1)q

Quit: branch to the end of the script. Do not start a new cycle.

(2)r rfilename

Read the contents of rfilename. Place them on the output before reading the next input line.

(2)s/regular expression/replacement/flags

Substitute the replacement string for instances of the regular expression in the pattern space. Any character may be used instead of `/'. For a fuller description see regexp(5). flags is zero or more of:

n

n= 1 - 512. Substitute for just the nth occurrence of the regularexpression.

g

Global: substitute for all nonoverlapping instances of the regular expression rather than just the first one.

p

Print the pattern space if a replacement was made.

w wfilename

Write: append the pattern space to wfilename if a replacement was made.

(2)t label

Test: branch to the `:' command bearing the label if any substitutions have been made since the most recent reading of an input line or execution of a t. If label is empty, branch to the end of the script.

(2)w wfilename

Write: append the pattern space to wfilename.

(2)x

Exchange the contents of the pattern and hold spaces.

(2)y/string1/string2/

Transform: replace all occurrences of characters in string1 with the corresponding character in string2. The lengths of string1 and string2 must be equal.

(2)! function

Do not: apply the function (or group, if function is `{') only to lines not selected by the address(es).

(0): label

This command does nothing; it bears a label for b and t commands to branch to. Note: the maximum length of label is seven characters.

(1)=

Place the current line number on the standard output as a line.

(2){

Execute the following commands through a matching `}' only when the pattern space is selected. Commands are separated by `;'.

(0)

An empty command is ignored.

See largefile(5) for the description of the behavior of sed when encountering files greater than or equal to 2 Gbyte ( 2³¹ bytes).