The sed(1) 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.
A single command may be specified as the first argument to
sed(1). Multiple commands can be specified by using the
-e or -f options. All commands are applied to the
input in the order they are specified regardless of their
origin.
The following options are available:
-a
The files listed as parameters for the w functions are
created (or truncated) before any processing begins, by default.
The -a option causes sed(1) to delay opening each
file until a command containing the related w function is
applied to a line of input.
-ecommand
Append the editing commands specified by the command
argument to the list of commands.
-fcommand_file
Append the editing commands found in the file
command_file to the list of commands. The editing commands
should each be listed on a separate line.
-n
By default, each line of input is echoed to the standard output
after all of the commands have been applied to it. The -n
option suppresses this behavior.
The form of a sed(1) command is as follows:
[address[,address]]function[arguments]
White space can be inserted before the first address and the
function portions of the command.
Normally, sed(1) cyclically copies a line of input, not
including its terminating newline character, into a pattern
space (unless there is something left after a 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.
Some of the functions use a hold space to save all or
part of the pattern space for subsequent retrieval.
The sed(1) commands do not require an address, but if one
is specified, it must be one of the following:
A number that counts input lines cumulatively across input
fields.
A dollar character ($) that addresses the last line of
input.
A context address that consists of a regular expression
surrounded by delimiter characters.
A command line with no addresses selects every pattern
space.
A command line with one address selects all of the pattern
spaces that match the address.
A command line with two addresses selects the inclusive range
from the first pattern space that matches the first address through
the next pattern space that matches the second. (If the second
address is a number less than or equal to the line number first
selected, only that line is selected.) Starting at the first line
following the selected range, sed(1) starts looking again
for the first address.
Editing commands can be applied to non-selected pattern spaces
by use of the exclamation character (!) function.
The sed(1) regular expressions are basic regular
expressions (BRE). The sed(1) utility also has the following
two additions to BREs:
In a context address, any character other than a backslash
(\) or newline character can be used to delimit the regular
expression. To do this, precede the first delimiting character with
a backslash. For example, to make x the delimiting
character for the BRE //*, you would type \x//*x. The second
x is automatically treated as the closing delimiter.
(This is often done to make it easier to type regular expressions
containing slashes.) Putting a backslash character before the
delimiting character causes the character to be treated literally.
For example, in the context address \xabc\xdefx, the RE delimiter
is an x and the second x stands for itself, so that
the regular expression is abcxdef.
The escape sequence \n 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.
One special feature of sed(1) regular expressions is that
they can default to the last regular expression used. If a regular
expression is empty (that is, 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
/abc/s//XXX/ will substitute XXX for the pattern
abc.
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.
The argument 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.
The r and 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 sed(1) is
created (or its contents truncated) before any input processing
begins.
The b, r, s, t, w, y,
!, and : functions all accept additional arguments.
The following synopses indicate which arguments have to be
separated from the function letters by white space characters.
Two of the functions take a function-list. This is a list of
sed(1) functions separated by newlines, as follows:
{ function
function
...
function
}
The { can be preceded by white space and can be followed
by white space. The function can be preceded by white space. The
terminating } must be preceded by a newline or optional
white space.
[2addr] function-list
Execute function-list only when the pattern space is selected.
[1addr]a\
text
Write text to standard output immediately before each
attempt to read a line of input, whether by executing the N
function or by beginning a new cycle.
[2addr]b[label]
Branch to the : function with the specified label. If
the label is not specified, branch to the end of the script.
[2addr]c\
text
Delete the pattern space. With 0 or 1 address or at the end of
a two-address range, text is written to the standard
output.
[2addr]d
Delete the pattern space and start the next cycle.
[2addr]D
Delete the initial segment of the pattern space through the
first newline character and start the next cycle.
[2addr]g
Replace the contents of the pattern space with the contents of
the hold space.
[2addr]G
Append a newline character followed by the contents of the hold
space to the pattern space.
[2addr]h
Replace the contents of the hold space with the contents of the
pattern space.
[2addr]H
Append a newline character followed by the contents of the
pattern space to the hold space.
[1addr]i\
text
Write text to the standard output.
[2addr]l
(The letter ell.) Write the pattern space to the standard
output in a visually unambiguous form. This form is as follows:
backslash
\
alert
\a
form-feed
\f
newline
\n
carriage-return
\r
tab
\t
vertical tab
\v
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 $.
[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.
[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.
[2addr]p
Write the pattern space to standard output.
[2addr]P
Write the pattern space, up to the first newline character to
the standard output.
[1addr]q
Branch to the end of the script and quit without starting a new
cycle.
[1addr]rfile
Copy the contents of file to the standard output
immediately before the next attempt to read a line of input. If
file cannot be read for any reason, it is silently ignored
and no error condition is set.
[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.
An ampersand (&) appearing in the replacement is
replaced by the string matching the RE. The special meaning of
& in this context can be suppressed by preceding it with
a backslash. The string \d, where d is a
digit, is replaced by the text matched by the corresponding
back-reference expression.
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.
The value of flags in the substitute function is zero or
more of the following:
0 ... 9
Make the substitution only for the Nth occurrence of the
regular expression in the pattern space.
g
Make the substitution for all non-overlapping matches of the
regular expression, not just the first one.
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.
wfile
Append the pattern space to 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.
[2addr]t [label]
Branch to the : function bearing the label if any
substitutions have been made since the most recent reading of an
input line or execution of a t function. If no label is
specified, branch to the end of the script.
[2addr]wfile
Append the pattern space to the file.
[2addr]x
Swap the contents of the pattern and hold spaces.
[2addr]y/string1/string2/
Replace all occurrences of characters in string1 in the
pattern space with the corresponding characters from
string2. Any character other than a backslash or newline can
be used instead of a slash to delimit the strings. Within
string1 and 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.
[2addr]!function
[2addr]!function-list
Apply the function or function-list only to the lines that are
not selected by the address(es).
[0addr]:label
This function does nothing; it bears a label to which the
b and t commands can branch.
[1addr]=
Write the line number to the standard output followed by a
newline character.
[0addr]
Empty lines are ignored.
[0addr]#
The # and the remainder of the line are ignored (treated
as a comment), unless the first two characters in the file
are #n, in which case the default output is suppressed. (This is
the same as specifying the -n option on the command
line.)
The sed(1) utility exits 0 on success and >0 if an
error occurs.