SED(1,C) AIX Commands Reference SED(1,C)
-------------------------------------------------------------------------------
sed
PURPOSE
Provides a stream editor.
SYNTAX
+------+ +------ "script" -------+ +------------+
sed ---| |---| +- -e --- "script" -+ |---| |---|
+- -n -+ +-| |-+ +--- file ---+
^+- -f --- sfile ----+| ^ |
+---------------------+ +--------+
DESCRIPTION
The sed command modifies lines from the specified file according to an edit
script and writes them to standard output. 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 subcommands is:
[address-range] function[modifiers]
The sed command processes each input file by reading an input line into a
pattern space, 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 is affected by the command. Otherwise, the
command is applied to all lines.
An address is either a decimal line number, a $ (dollar sign), which addresses
the last line of input, or a context address. A context address is a regular
expression similar to those used in ed except for the following differences:
o You can select the character delimiter for patterns. The general form of
the expression is:
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\?pattern?
where ? is a character delimiter you select. This delimiter must be a
1-byte character. The default form for the pattern is:
/pattern/
o The sequence \n matches a new-line character in the pattern space, except
the terminating new line.
o A . (dot) matches any character except a terminating new-line character.
That is, unlike ed, which cannot match a new-line character in the middle
of a line, sed can match a new-line character in the pattern space.
Certain commands allow you to specify one line or a range of lines to which the
command should be applied. These commands are called addressed commands. The
following rules apply to addressed commands:
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 commas 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.
Notes:
1. The text parameter accompanying the a\, c\, and i\ commands can continue
onto more than one line provided all lines but the last end with a \ to
quote the new-line character. Backslashes in text are treated like
backslashes in the replacement string of an s command and can be used to
protect initial blanks and tabs against the stripping that is done on every
script line. The rfile and wfile parameters must end the command line and
must be preceded by exactly one blank. Each wfile is created before
processing begins.
2. The sed command can process up to 99 commands in a pattern file.
FLAGS
-e "script" Uses the text "script" as the editing script. If you are using
just one -e flag and no -f flag, the -e flag may be omitted.
-f sfile Uses sfile as the source of the edit script. sfile is a prepared
set of editing commands to be applied to file.
-n Suppresses all information normally written to standard output.
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PARAMETERS
In the following list of functions, the maximum number of permissible addresses
for each function is indicated in parentheses. The sed script subcommands are
as follows:
(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 0 or 1 address or at the end of a
2-address range, places text on the output. Starts the next cycle.
(2)d Deletes the pattern space. Starts the next cycle.
(2)D Deletes the initial segment of the pattern space through the first
new-line character. Starts the next cycle.
(2)g Replaces the contents of the pattern space by 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 by the contents 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 nondisplayable
characters as two-digit octal values. Long lines are folded.
(2)n Writes the pattern space to standard output. 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
new-line character. (The current line number changes.) You can use
this to search for patterns that may be split onto two lines.
(2)p Writes the pattern space to standard output if a replacement was made
and the default output has been suppressed (by using the -n option on
the command line or the #n command in the script).
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(2)P Writes the initial segment of the pattern space through the first
new-line character to standard output.
(1)q Branches to the end of the script. Does not start a new cycle.
(1)r rfile
Reads the contents of rfile. 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 appearing after the s can
substitute for the / separator.
You can add zero or more of the following flags:
g Substitutes all non-overlapping instances of the pattern rather
than just the first one.
p Writes the pattern space to standard out if a replacement was made.
w wfile
Writes the pattern space to wfile if a replacement was made.
Appends the pattern space to wfile. If wfile was not already
created by a previous write by this sed script, sed creates it.
(2)tlabel
Branches to :label in the script file if any substitutions 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)wwfile
Appends the pattern space to wfile.
(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 pattern2. The byte lengths of pattern1 and
pattern2 must be equal.
(2)!sed-cmd
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.
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(2){subcmd
.
.
.
} Groups subcommands enclosed in {} (braces).
# If a # appears as the first character on the first line of a script
file, then that entire line is treated as a comment, with one
exception. If the character after the # is an "n", then the default
output is suppressed. The rest of the line after "#n" is also
ignored. A script file must contain at least one non-comment line.
EXAMPLES
1. To perform a global change:
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 version 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. Without 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 output. 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:
pr chap2 | sed "s/Page *[0-9]*$/(&)/" | print
This encloses the page numbers in parentheses before printing "chap2". The
pr command puts a heading and page number at the top of each page, then sed
puts the page numbers in parentheses, and the print command prints the
edited listing.
The sed pattern "/Page *[0-9]*$/" matches page numbers that appear at the
end of a line. The s subcommand changes this to "(&)", where the "&"
(ampersand) stands for the page number that was matched.
3. To display selected lines of a file:
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 subcommands like p to
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write specific parts of the text. Without the -n, this example would
display all the lines in "chap3", and it would show each line containing
"food" twice.
4. To perform complex editing:
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 very 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 file:
: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, imbedding a new-line character. The "s/\\\n//"
deletes the \ and imbedded new-line character. Finally, b" join" branches
back to the label ":join" to check for a \ at the end of the newly joined
line. Without the branch, sed writes the joined line and read the next one
before checking for a second \.
Note: 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 stopping.
This means that if the last line of the input ends with a \, it is
not copied to the output.
RELATED INFORMATION
See the following commands: "awk, nawk, oawk," "ed, red," and "grep, egrep,
fgrep."
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