Sed is a stream editor.
A stream editor is used to perform basic text
transformations on an input stream
(a file or input from a pipeline).
While in some ways similar to an editor which
permits scripted edits (such as ed),
sed works by making only one pass over the
input(s), and is consequently more efficient.
But it is sed’s ability to filter text in a pipeline
which particularly distinguishes it from other types of
editors.
-n, --quiet, --silent
suppress automatic printing of pattern space
-e script, --expression=script
add the script to the commands to be executed
-f script-file, --file=script-file
add the contents of script-file to the commands to be executed
--follow-symlinks
follow symlinks when processing in place
-i[SUFFIX], --in-place[=SUFFIX]
edit files in place (makes backup if extension supplied)
-l N, --line-length=N
specify the desired line-wrap length for the ‘l’ command
--posix
disable all GNU extensions.
-r, --regexp-extended
use extended regular expressions in the script.
-s, --separate
consider files as separate rather than as a single continuous
long stream.
-u, --unbuffered
load minimal amounts of data from the input files and flush
the output buffers more often
--help
display this help and exit
--version
output version information and exit
If no -e, --expression, -f, or --file option is given, then the first
non-option argument is taken as the sed script to interpret. All
remaining arguments are names of input files; if no input files are
specified, then the standard input is read.
This is just a brief synopsis of sed commands to serve as
a reminder to those who already know sed;
other documentation (such as the texinfo document)
must be consulted for fuller descriptions.
Zero-address ‘‘commands’’
: label
Label for
b and
t commands.
#comment
The comment extends until the next newline (or the end of a
-e script fragment).
}
The closing bracket of a { } block.
Zero- or One- address commands
=
Print the current line number.
a \
text
Append
text, which has each embedded newline preceded by a backslash.
i \
text
Insert
text, which has each embedded newline preceded by a backslash.
q [exit-code]
Immediately quit the sed script without processing
any more input, except that if auto-print is not disabled
the current pattern space will be printed. The exit code
argument is a GNU extension.
Q [exit-code]
Immediately quit the sed script without processing
any more input. This is a GNU extension.
r filename
Append text read from
filename.
R filename
Append a line read from
filename. Each invocation of the command reads a line from the file.
This is a GNU extension.
Commands which accept address ranges
{
Begin a block of commands (end with a }).
b label
Branch to
label; if
label is omitted, branch to end of script.
c \
text
Replace the selected lines with
text, which has each embedded newline preceded by a backslash.
d
Delete pattern space.
Start next cycle.
D
Delete up to the first embedded newline in the pattern space.
Start next cycle, but skip reading from the input
if there is still data in the pattern space.
h H
Copy/append pattern space to hold space.
g G
Copy/append hold space to pattern space.
l
List out the current line in a ‘‘visually unambiguous’’ form.
l width
List out the current line in a ‘‘visually unambiguous’’ form,
breaking it at
width characters. This is a GNU extension.
n N
Read/append the next line of input into the pattern space.
p
Print the current pattern space.
P
Print up to the first embedded newline of the current pattern space.
s/regexp/replacement/
Attempt to match
regexp against the pattern space.
If successful, replace that portion matched
with
replacement. The
replacement may contain the special character
& to refer to that portion of the pattern space which matched,
and the special escapes \1 through \9 to refer to the
corresponding matching sub-expressions in the
regexp.
t label
If a s/// has done a successful substitution since the
last input line was read and since the last t or T
command, then branch to
label; if
label is omitted, branch to end of script.
T label
If no s/// has done a successful substitution since the
last input line was read and since the last t or T
command, then branch to
label; if
label is omitted, branch to end of script. This is a GNU
extension.
w filename
Write the current pattern space to
filename.
W filename
Write the first line of the current pattern space to
filename. This is a GNU extension.
x
Exchange the contents of the hold and pattern spaces.
y/source/dest/
Transliterate the characters in the pattern space which appear in
source to the corresponding character in
dest.
Addresses
Sed commands can be given with no addresses, in which
case the command will be executed for all input lines;
with one address, in which case the command will only be executed
for input lines which match that address; or with two
addresses, in which case the command will be executed
for all input lines which match the inclusive range of
lines starting from the first address and continuing to
the second address.
Three things to note about address ranges:
the syntax is
addr1,addr2 (i.e., the addresses are separated by a comma);
the line which
addr1 matched will always be accepted,
even if
addr2 selects an earlier line;
and if
addr2 is a
regexp, it will not be tested against the line that
addr1 matched.
After the address (or address-range),
and before the command, a
! may be inserted,
which specifies that the command shall only be
executed if the address (or address-range) does
not match.
The following address types are supported:
number
Match only the specified line
number.
first~step
Match every
step’th line starting with line
first. For example, ‘‘sed -n 1~2p’’ will print all the odd-numbered lines in
the input stream, and the address 2~5 will match every fifth line,
starting with the second.
first can be zero; in this case, sed operates as if it were equal to
step. (This is an extension.)
$
Match the last line.
/regexp/
Match lines matching the regular expression
regexp.
\cregexpc
Match lines matching the regular expression
regexp. The
c may be any character.
GNU sed also supports some special 2-address forms:
0,addr2
Start out in "matched first address" state, until
addr2 is found.
This is similar to
1,addr2, except that if
addr2 matches the very first line of input the
0,addr2 form will be at the end of its range, whereas the
1,addr2 form will still be at the beginning of its range.
This works only when
addr2 is a regular expression.
addr1,+N
Will match
addr1 and the
N lines following
addr1.
addr1,~N
Will match
addr1 and the lines following
addr1 until the next line whose input line number is a multiple of
N.
POSIX.2 BREs
should be supported, but they aren’t completely because of performance
problems.
The
\n sequence in a regular expression matches the newline character,
and similarly for
\a,
\t, and other sequences.
E-mail bug reports to
bonzini@gnu.org. Be sure to include the word ‘‘sed’’ somewhere in the ‘‘Subject:’’ field.
Also, please include the output of ‘‘sed --version’’ in the body
of your report if at all possible.