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Man Page for SedNAME
sed - Provides a stream line editor
SYNOPSIS
sed [-n] [-e script ...] [-f source-file] [file ...]
sed [-n] [script] [file ...]
The sed command modifies lines from the specified
file or from standard input according to edit com-
mands and writes them to standard output.
DESCRIPTION
The sed command includes many features for selecting lines
to be modified and making changes only to the selected
lines.
The sed command uses two work spaces for holding the line
being modified: the pattern space, where the selected
line is held, and the hold space, where a line can be
stored temporarily.
An edit script consists of individual subcommands, each
one on a separate line. The general form of sed subcom-
mands is as follows:
[address_range] function [modifier ...]
The sed command processes each input file by reading an
input line into a pattern space, sequentially applying all
sed subcommands in sequence whose addresses select that
line, and writing the pattern space to standard output.
It then clears the pattern space and repeats this process
for each line in the input file. Some of the subcommands
use a hold space to save all or part of the pattern space
for subsequent retrieval.
When a command includes an address, either a line number
or a search pattern, only the addressed line or lines are
affected by the command. Otherwise, the command is
applied to all lines.
sed Addresses
An address is either a decimal line number, a $,
which addresses the last line of input, or a con-
text address. A context address is a regular
expression (R.E.) as described for grep, except
that you can select the character delimiter for
patterns. The general form of the expression is as
follows:
\?pattern\?
The ? represents a character delimiter you select. This
delimiter cannot be a 2-byte international character sup-
port extended character.
The default form for the pattern is as follows:
/pattern/
o In a context address, the construction \cexpressionc,
where c is any character other than a \ (backslash)
or the newline character, is identical to /expres-
sion/. If the character designated by c appears fol-
lowing a \ (backslash), then it is considered to be
that literal character, which does not terminate the
RE. For example, in the context address \xabc\xdefx,
the second x stands for itself, so that the regular
expression is abcxdef.
o The sequence \n matches a newline character in the
pattern space, except the terminating new line.
o A . (dot) matches any character except a terminating
newline character. That is, unlike grep, which can-
not match a newline character in the middle of a
line, sed can match a newline character in the pat-
tern space.
Certain commands allow you to specify one line or a range of
lines to which the command applies. These commands are called
addressed commands. The following rules apply to addressed com-
mands:
o A command line with no address selects every line.
o A command line with one address, expressed in context form,
selects each line that matches the address.
o A command line with two addresses separated by a , (comma)
or ; (semicolon) selects the entire range from the first
line that matches the first address through the next line
that matches the second. (If the second address is a number
less than or equal to the line number first selected, only
one line is selected.) Thereafter, the process is repeated,
looking again for the first address.
FLAGS
-e script
Uses the string script as an editing script. If you
are using just one -e flag and no -f flag, you can
omit the -e flag and include the single script on the
command line as an argument to sed.
-f source_file
Uses source_file as the source of the edit script.
The source_file is a set of editing commands to be
applied to file.
-n Suppresses all information normally written to stan-
dard output.
Subcommands
Backslashes in text are treated like backslashes in the
replacement string of an s command and can be used to pro-
tect initial spaces and tabs against the stripping that is
done on every script line.
The text argument accompanying the a\, c\, and i\ commands
can continue onto more than one line, provided all lines
but the last end with a \ (backslash) to quote the newline
character.
The read_file and write_file arguments must end the com-
mand line and must be preceded by exactly one space. Each
write_file is created before processing begins.
The sed command can process up to 99 commands in a file.
In the following list of subcommands, the maximum number
of permissible addresses for each subcommand is indicated
in parentheses. The sed script subcommands are as fol-
lows:
(2){subcommand ...
} Groups subcommands enclosed in { } (braces). The {
(left brace) can be preceded by spaces and can be fol-
lowed by spaces or tabs. The list of subcommands must
be separated by newline characters. The subcommands
can also be preceded by spaces or tabs. The terminat-
ing } (right brace) must be preceded by a newline
character and then zero or more spaces.
(1) a\
text
Places text on the output before reading the next
input line.
(2)b[label]
Branches to the : command bearing the label. If label
is empty, it branches to the end of the script.
(2)c\
text
Deletes the pattern space. With a 0 or 1 address or
at the end of a 2-address range, places text on the
output. Then it starts the next cycle.
(2)d
Deletes the pattern space. Then it starts the next
cycle.
(2)D
Deletes the initial segment of the pattern space
through the first newline character. Then it starts
the next cycle.
(2)g
Replaces the contents of the pattern space with the
contents of the hold space.
(2)G
Appends the contents of the hold space to the pattern
space.
(2)h
Replaces the contents of the hold space with the con-
tents of the pattern space.
(2)H
Appends the contents of the pattern space to the hold
space.
(1)i\
text
Writes text to standard output before reading the next
line into the pattern space.
(2)l
Writes the pattern space to standard output, showing
nonprinting characters as 3-digit octal values. Long
lines are folded, with the point of folding indicated
by <Backslash><Return>. The end of each line is
marked with a $.
Certain characters are shown as escape sequences as
follows:
\\ Backslash
\a Alert
\b Backspace
\f Formfeed
\n Newline
\r Carriage-return
\t Tab
\v Vertical tab
(2)n
Writes the pattern space to standard output. It
replaces the pattern space with the next line of
input.
(2)N
Appends the next line of input to the pattern space
with an embedded newline character. (The current line
number changes.) You can use this to search for pat-
terns that are split onto two lines.
(2)p
Writes the pattern space to standard output.
(2)P
Writes the initial segment of the pattern space
through the first newline character to standard out-
put.
(1)q
Branches to the end of the script. It does not start
a new cycle.
(1)r read_file
Reads the contents of read_file. It places contents
on the output before reading the next input line.
(2)s/pattern/replacement/flags
Substitutes the replacement string for the first
occurrence of the pattern in the pattern space. Any
character that is entered after the s command can sub-
stitute for the / (slash) separator, except \ (back-
slash) and the newline character. Within the regular
expression and replacement string, the delimiter can
appear as a literal if it is preceded by a \ (back-
slash).
An & (ampersand) appearing in the replacement string
is replaced by the string matching the RE. The spe-
cial meaning of & in this context can be suppressed by
preceding it with a \ (backslash). The characters \n,
where n is a digit, are replaced by the text matched
by the corresponding backreference expression.
A line can be split by substituting a newline charac-
ter into it. You must escape the newline character in
the replacement string by preceding it with a \ back-
slash. A substitution is considered to have been per-
formed even if the replacement string is identical to
the string that it replaces.
You can add zero or more of the following flags:
n Where n is 1-512, substitutes replacement for the
nth occurrence of pattern on each addressed line,
rather than for the first occurrence.
g Substitutes replacement for all nonoverlapping
instances of pattern on each addressed line,
rather than for just the first one (or for the one
specified by n).
p Writes the pattern space to standard output if a
replacement was made.
w write_file
Writes the pattern space to write_file if a
replacement was made. Appends the pattern space
to write_file. If write_file was not already cre-
ated by a previous write by this sed script, sed
creates it. Each write_file is created before
processing begins.
(2)t[label]
Branches to :label in the script file if any substitu-
tions were made since the most recent reading of an
input line execution of a t subcommand. If you do not
specify label, control transfers to the end of the
script.
(2)w write_file
Appends the pattern space to write_file.
(2)x
Exchanges the contents of the pattern space and the
hold space.
(2)y/pattern1/pattern2/
Replaces all occurrences of characters in pattern1
with the corresponding characters from pattern2. The
byte lengths of pattern1 and pattern2 must be equal.
(2)!sed_command
Applies the specified sed subcommand only to lines not
selected by the address or addresses.
(0):label
This script entry simply marks a branch point to be
referenced by the b and t commands. This label can be
any sequence of eight or fewer bytes.
(1)=
Writes the current line number to standard output as a
line.
(2){subcommand ...
} Groups subcommands enclosed in { } (braces).
(0) Ignores an empty command.
(0)#
If a # (number sign) appears as the first character on
the first line of a script file, that entire line is
treated as a comment, with one exception. If the
character after the # is an n, the default output is
suppressed. The rest of the line after the #n is
ignored. A script must contain at least one noncom-
ment line.
RESTRICTIONS
The h subcommand for sed does not work properly. When you
use the h subcommand to place text into the hold area,
only the last line of the specified text is saved. You
can use the H subcommand to append text to the hold area.
The H subcommand and all others dealing with the hold area
work correctly.
EXAMPLES
1. To perform a global change, enter:
sed "s/happy/enchanted/g" chap1 >chap1.new
This replaces each occurrence of happy found in the
file chap1 with enchanted, and puts the edited ver-
sion in a separate file named chap1.new. The g at
the end of the s subcommand tells sed to make as
many substitutions as possible on each line. With-
out the g, sed replaces only the first happy on a
line.
The sed stream editor operates as a filter. It
reads text from standard input or from the files
named on the command line (chap1 in this example),
modifies this text, and writes it to standard out-
put. Unlike most editors, it does not replace the
original file. This makes sed a powerful command
when used in pipelines.
2. To use sed as a filter in a pipeline (sh only),
enter:
pr chap2 | sed "s/Page *[0-9]*$/(&)/" | print
This encloses the page numbers in parentheses
before printing chap2. The pr command puts a head-
ing and page number at the top of each page, then
sed puts the page numbers in parentheses, and the
print command prints the edited listing.
The sed pattern /Page *[0-9]*$/ matches page num-
bers that appear at the end of a line. The s sub-
command changes this to (&), where the & stands for
the pattern that was matched (for example, Page
5).
3. To display selected lines of a file, enter:
sed -n "/food/p" chap3
This displays each line in chap3 that contains the
word food. Normally, sed copies every line to
standard output after it is edited. The -n flag
stops sed from doing this. You then use subcom-
mands like p to write specific parts of the text.
Without the -n, this example displays all the lines
in chap3, and it shows each line containing food
twice.
4. To perform complex editing, enter:
sed -f script.sed chap4 >chap4.new
It is always a good idea to create a sed script
file when you want to do anything complex. You can
then test and modify your script before using it.
You can also reuse your script to edit other files.
Create the script file with an interactive text
editor.
5. A sample sed script follows:
:join
/\\$/{N
s/\\\n//
b join
}
This sed script joins each line that ends with a \
(backslash) to the line that follows it. First,
the pattern /\\$/ selects a line that ends with a \
for the group of commands enclosed in { }. The N
subcommand then appends the next line, embedding a
newline character. The s/\\\n// deletes the \
(backslash) and embedded newline character.
Finally, b join branches back to the label :join to
check for a \ (backslash) at the end of the newly
joined line. Without the branch, sed writes the
joined line and reads the next one before checking
for a second \ character.
The N subcommand causes sed to stop immediately if
there are no more lines of input (that is, if N
reads the End-of-File character). It does not copy
the pattern space to standard output before stop-
ping. This means that if the last line of the
input ends with a \ (backslash) character, then it
is not copied to the output.
RELATED INFORMATION
Commands: awk(1), grep(1)/egrep(1)/fgrep(1),
vi(1)/vedit(1)/view(1).
Programming Support Tools delim off
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