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Originalno upustvo za SED iz 1978.

by milobit last modified Aug 04, 2006 02:42 PM
SED - A Non-interactive Text Editor

SED - A Non-interactive Text Editor


Lee E. McMahon

Context search
Editing

ABSTRACT


Sed is a non-interactive context editor that
runs on the UNIX- operating system. Sed is
designed to be especially useful in three cases:

1) To edit files too large for comfortable
interactive editing;
2) To edit any size file when the sequence of
editing commands is too complicated to
be comfortably typed in interactive
mode.
3) To perform multiple `global' editing func-
tions efficiently in one pass through
the input.

This memorandum constitutes a manual for users of
sed.

August 15, 1978

_________________________
- UNIX is a trademark of Bell Laboratories.

SED - A Non-interactive Text Editor


Lee E. McMahon

Context search
Editing

Introduction


Sed is a non-interactive context editor designed to be espe-
cially useful in three cases:

1) To edit files too large for comfortable interactive
editing;
2) To edit any size file when the sequence of editing
commands is too complicated to be comfortably
typed in interactive mode;
3) To perform multiple `global' editing functions effi-
ciently in one pass through the input.

Since only a few lines of the input reside in core at one
time, and no temporary files are used, the effective size of
file that can be edited is limited only by the requirement
that the input and output fit simultaneously into available
secondary storage.

Complicated editing scripts can be created separately and
given to sed as a command file. For complex edits, this
saves considerable typing, and its attendant errors. Sed
running from a command file is much more efficient than any
interactive editor known to the author, even if that editor
can be driven by a pre-written script.

The principal loss of functions compared to an interactive
editor are lack of relative addressing (because of the
line-at-a-time operation), and lack of immediate verifica-
tion that a command has done what was intended.

Sed is a lineal descendant of the UNIX editor, ed. Because
of the differences between interactive and non-interactive
operation, considerable changes have been made between ed
and sed; even confirmed users of ed will frequently be
surprised (and probably chagrined), if they rashly use sed
without reading Sections 2 and 3 of this document. The most
striking family resemblance between the two editors is in
the class of patterns (`regular expressions') they recog-
nize; the code for matching patterns is copied almost verba-
tim from the code for ed, and the description of regular

expressions in Section 2 is copied almost verbatim from the
UNIX Programmer's Manual[1]. (Both code and description were
written by Dennis M. Ritchie.)

1. Overall Operation


Sed by default copies the standard input to the standard
output, perhaps performing one or more editing commands on
each line before writing it to the output. This behavior
may be modified by flags on the command line; see Section
1.1 below.

The general format of an editing command is:

[address1,address2][function][arguments]

One or both addresses may be omitted; the format of
addresses is given in Section 2. Any number of blanks or
tabs may separate the addresses from the function. The
function must be present; the available commands are dis-
cussed in Section 3. The arguments may be required or
optional, according to which function is given; again, they
are discussed in Section 3 under each individual function.

Tab characters and spaces at the beginning of lines are
ignored.

1.1. Command-line Flags


Three flags are recognized on the command line:
-n: tells sed not to copy all lines, but only those
specified by p functions or p flags after s func-
tions (see Section 3.3);
-e: tells sed to take the next argument as an editing
command;
-f: tells sed to take the next argument as a file name;
the file should contain editing commands, one to a
line.

1.2. Order of Application of Editing Commands


Before any editing is done (in fact, before any input file
is even opened), all the editing commands are compiled into
a form which will be moderately efficient during the execu-
tion phase (when the commands are actually applied to lines
of the input file). The commands are compiled in the order
in which they are encountered; this is generally the order
in which they will be attempted at execution time. The com-
mands are applied one at a time; the input to each command
is the output of all preceding commands.

The default linear order of application of editing commands
can be changed by the flow-of-control commands, t and b (see
Section 3). Even when the order of application is changed
by these commands, it is still true that the input line to
any command is the output of any previously applied command.

1.3. Pattern-space


The range of pattern matches is called the pattern space.
Ordinarily, the pattern space is one line of the input text,
but more than one line can be read into the pattern space by
using the N command (Section 3.6.).

1.4. Examples


Examples are scattered throughout the text. Except where
otherwise noted, the examples all assume the following input
text:

In Xanadu did Kubla Khan
A stately pleasure dome decree:
Where Alph, the sacred river, ran
Through caverns measureless to man
Down to a sunless sea.

(In no case is the output of the sed commands to be con-
sidered an improvement on Coleridge.)


Example:

The command

2q

will quit after copying the first two lines of the input.
The output will be:

In Xanadu did Kubla Khan
A stately pleasure dome decree:

2. ADDRESSES: Selecting lines for editing


Lines in the input file(s) to which editing commands are to
be applied can be selected by addresses. Addresses may be
either line numbers or context addresses.

The application of a group of commands can be controlled by
one address (or address-pair) by grouping the commands with
curly braces (`{ }')(Sec. 3.6.).

2.1. Line-number Addresses


A line number is a decimal integer. As each line is read
from the input, a line-number counter is incremented; a
line-number address matches (selects) the input line which
causes the internal counter to equal the address line-
number. The counter runs cumulatively through multiple
input files; it is not reset when a new input file is
opened.

As a special case, the character $ matches the last line of
the last input file.

2.2. Context Addresses


A context address is a pattern (`regular expression')
enclosed in slashes (`/'). The regular expressions recog-
nized by sed are constructed as follows:

1) An ordinary character (not one of those discussed
below) is a regular expression, and matches that
character.
2) A circumflex `^' at the beginning of a regular
expression matches the null character at the
beginning of a line.
3) A dollar-sign `$' at the end of a regular expression
matches the null character at the end of a line.
4) The characters `\n' match an imbedded newline char-
acter, but not the newline at the end of the pat-
tern space.
5) A period `.' matches any character except the termi-
nal newline of the pattern space.
6) A regular expression followed by an asterisk `*'
matches any number (including 0) of adjacent
occurrences of the regular expression it follows.
7) A string of characters in square brackets `[ ]'
matches any character in the string, and no oth-
ers. If, however, the first character of the
string is circumflex `^', the regular expression
matches any character except the characters in the
string and the terminal newline of the pattern
space.
8) A concatenation of regular expressions is a regular
expression which matches the concatenation of
strings matched by the components of the regular
expression.
9) A regular expression between the sequences `\(' and
`\)' is identical in effect to the unadorned regu-
lar expression, but has side-effects which are
described under the s command below and specifica-
tion 10) immediately below.
10) The expression `\d' means the same string of char-
acters matched by an expression enclosed in `\('
and `\)' earlier in the same pattern. Here d is a
single digit; the string specified is that begin-
ning with the dth occurrence of `\(' counting from
the left. For example, the expression `^\(.*\)\1'
matches a line beginning with two repeated
occurrences of the same string.
11) The null regular expression standing alone (e.g.,
`//') is equivalent to the last regular expres-
sion compiled.

To use one of the special characters (^ $ . * [ ] \ /) as a
literal (to match an occurrence of itself in the input),
precede the special character by a backslash `\'.

For a context address to `match' the input requires that the
whole pattern within the address match some portion of the
pattern space.

2.3. Number of Addresses


The commands in the next section can have 0, 1, or 2
addresses. Under each command the maximum number of allowed
addresses is given. For a command to have more addresses
than the maximum allowed is considered an error.

If a command has no addresses, it is applied to every line
in the input.

If a command has one address, it is applied to all lines
which match that address.

If a command has two addresses, it is applied to the first
line which matches the first address, and to all subsequent
lines until (and including) the first subsequent line which
matches the second address. Then an attempt is made on sub-
sequent lines to again match the first address, and the pro-
cess is repeated.

Two addresses are separated by a comma.

Examples:

/an/ matches lines 1, 3, 4 in our sample text
/an.*an/ matches line 1
/^an/ matches no lines
/./ matches all lines
/\./ matches line 5
/r*an/ matches lines 1,3, 4 (number = zero!)
/\(an\).*\1/ matches line 1

3. FUNCTIONS


All functions are named by a single character. In the
following summary, the maximum number of allowable addresses
is given enclosed in parentheses, then the single character
function name, possible arguments enclosed in angles (< >),
an expanded English translation of the single-character
name, and finally a description of what each function does.
The angles around the arguments are not part of the argu-
ment, and should not be typed in actual editing commands.

3.1. Whole-line Oriented Functions


(2)d -- delete lines The d function deletes from the
file (does not write to the output) all those
lines matched by its address(es). It also has the
side effect that no further commands are attempted
on the corpse of a deleted line; as soon as the d
function is executed, a new line is read from the
input, and the list of editing commands is re-
started from the beginning on the new line.
(2)n -- next line The n function reads the next line
from the input, replacing the current line. The
current line is written to the output if it should
be. The list of editing commands is continued
following the n command.
(1)a\
<text> -- append lines
The a function causes the argument <text> to be
written to the output after the line matched by
its address. The a command is inherently multi-
line; a must appear at the end of a line, and
<text> may contain any number of lines. To
preserve the one-command-to-a-line fiction, the
interior newlines must be hidden by a backslash
character (`\') immediately preceding the newline.
The <text> argument is terminated by the first
unhidden newline (the first one not immediately
preceded by backslash). Once an a function is
successfully executed, <text> will be written to
the output regardless of what later commands do to
the line which triggered it. The triggering line
may be deleted entirely; <text> will still be
written to the output. The <text> is not scanned
for address matches, and no editing commands are
attempted on it. It does not cause any change in
the line-number counter.
(1)i\
<text> -- insert lines
The i function behaves identically to the a func-
tion, except that <text> is written to the output
before the matched line. All other comments about
the a function apply to the i function as well.
(2)c\
<text> -- change lines
The c function deletes the lines selected by its
address(es), and replaces them with the lines in
<text>. Like a and i, c must be followed by a
newline hidden by a backslash; and interior new
lines in <text> must be hidden by backslashes.
The c command may have two addresses, and there-
fore select a range of lines. If it does, all the
lines in the range are deleted, but only one copy
of <text> is written to the output, not one copy
per line deleted. As with a and i, <text> is not
scanned for address matches, and no editing com-
mands are attempted on it. It does not change the
line-number counter. After a line has been
deleted by a c function, no further commands are
attempted on the corpse. If text is appended
after a line by a or r functions, and the line is
subsequently changed, the text inserted by the c
function will be placed before the text of the a
or r functions. (The r function is described in
Section 3.4.)
Note: Within the text put in the output by these functions,
leading blanks and tabs will disappear, as always in sed
commands. To get leading blanks and tabs into the output,
precede the first desired blank or tab by a backslash; the
backslash will not appear in the output.

Example:

The list of editing commands:

n
a\
XXXX
d

applied to our standard input, produces:

In Xanadu did Kubhla Khan
XXXX
Where Alph, the sacred river, ran
XXXX
Down to a sunless sea.

In this particular case, the same effect would be produced
by either of the two following command lists:

n n
i\ c\
XXXX XXXX
d

3.2. Substitute Function


One very important function changes parts of lines selected
by a context search within the line.

(2)s<pattern><replacement><flags> -- substitute The s
function replaces part of a line (selected by
<pattern>) with <replacement>. It can best be
read:
Substitute for <pattern>, <replacement>
The <pattern> argument contains a pattern, exactly
like the patterns in addresses (see 2.2 above).
The only difference between <pattern> and a con-
text address is that the context address must be
delimited by slash (`/') characters; <pattern> may
be delimited by any character other than space or
newline. By default, only the first string
matched by <pattern> is replaced, but see the g
flag below. The <replacement> argument begins
immediately after the second delimiting character
of <pattern>, and must be followed immediately by
another instance of the delimiting character.
(Thus there are exactly three instances of the
delimiting character.) The <replacement> is not a
pattern, and the characters which are special in
patterns do not have special meaning in <replace-
ment>. Instead, other characters are special:
& is replaced by the string matched by
<pattern>
\d (where d is a single digit) is replaced by
the dth substring matched by parts of
<pattern> enclosed in `\(' and `\)'. If
nested substrings occur in <pattern>,
the dth is determined by counting open-
ing delimiters (`\('). As in patterns,
special characters may be made literal
by preceding them with backslash (`\').
The <flags> argument may contain the following
flags:
g -- substitute <replacement> for all (non-
overlapping) instances of <pattern> in
the line. After a successful substitu-
tion, the scan for the next instance of
<pattern> begins just after the end of
the inserted characters; characters put
into the line from <replacement> are not
rescanned.
p -- print the line if a successful replace-
ment was done. The p flag causes the
line to be written to the output if and
only if a substitution was actually made
by the s function. Notice that if
several s functions, each followed by a
p flag, successfully substitute in the
same input line, multiple copies of the
line will be written to the output: one
for each successful substitution.
w <filename> -- write the line to a file if a
successful replacement was done. The w
flag causes lines which are actually
substituted by the s function to be
written to a file named by <filename>.
If <filename> exists before sed is run,
it is overwritten; if not, it is
created. A single space must separate w
and <filename>. The possibilities of
multiple, somewhat different copies of
one input line being written are the
same as for p. A maximum of 10 dif-
ferent file names may be mentioned after
w flags and w functions (see below),
combined.

Examples:

The following command, applied to our standard input,

s/to/by/w changes

produces, on the standard output:

In Xanadu did Kubhla Khan
A stately pleasure dome decree:
Where Alph, the sacred river, ran
Through caverns measureless by man
Down by a sunless sea.

and, on the file `changes':

Through caverns measureless by man
Down by a sunless sea.

If the nocopy option is in effect, the command:

s/[.,;?:]/*P&*/gp

produces:

A stately pleasure dome decree*P:*
Where Alph*P,* the sacred river*P,* ran
Down to a sunless sea*P.*

Finally, to illustrate the effect of the g flag, the com-
mand:

/X/s/an/AN/p

produces (assuming nocopy mode):

In XANadu did Kubhla Khan

and the command:

/X/s/an/AN/gp

produces:

In XANadu did Kubhla KhAN

3.3. Input-output Functions


(2)p -- print The print function writes the addressed
lines to the standard output file. They are writ-
ten at the time the p function is encountered,
regardless of what succeeding editing commands may
do to the lines.
(2)w <filename> -- write on <filename> The write func-
tion writes the addressed lines to the file named
by <filename>. If the file previously existed, it
is overwritten; if not, it is created. The lines
are written exactly as they exist when the write
function is encountered for each line, regardless
of what subsequent editing commands may do to
them. Exactly one space must separate the w and
<filename>. A maximum of ten different files may
be mentioned in write functions and w flags after
s functions, combined.
(1)r <filename> -- read the contents of a file The read
function reads the contents of <filename>, and
appends them after the line matched by the
address. The file is read and appended regardless
of what subsequent editing commands do to the line
which matched its address. If r and a functions
are executed on the same line, the text from the a
functions and the r functions is written to the
output in the order that the functions are exe-
cuted. Exactly one space must separate the r and
<filename>. If a file mentioned by a r function
cannot be opened, it is considered a null file,
not an error, and no diagnostic is given.
NOTE: Since there is a limit to the number of files that can
be opened simultaneously, care should be taken that no more
than ten files be mentioned in w functions or flags; that
number is reduced by one if any r functions are present.
(Only one read file is open at one time.)

Examples

Assume that the file `note1' has the following contents:

Note: Kubla Khan (more properly Kublai Khan;
1216-1294) was the grandson and most eminent suc-
cessor of Genghiz (Chingiz) Khan, and founder of
the Mongol dynasty in China.

Then the following command:

/Kubla/r note1

produces:

In Xanadu did Kubla Khan
Note: Kubla Khan (more properly Kublai Khan;
1216-1294) was the grandson and most eminent suc-
cessor of Genghiz (Chingiz) Khan, and founder of
the Mongol dynasty in China.
A stately pleasure dome decree:
Where Alph, the sacred river, ran
Through caverns measureless to man
Down to a sunless sea.

3.4. Multiple Input-line Functions


Three functions, all spelled with capital letters, deal spe-
cially with pattern spaces containing imbedded newlines;
they are intended principally to provide pattern matches
across lines in the input.
(2)N -- Next line The next input line is appended to
the current line in the pattern space; the two
input lines are separated by an imbedded newline.
Pattern matches may extend across the imbedded
newline(s).
(2)D -- Delete first part of the pattern space Delete
up to and including the first newline character in
the current pattern space. If the pattern space
becomes empty (the only newline was the terminal
newline), read another line from the input. In
any case, begin the list of editing commands again
from its beginning.
(2)P -- Print first part of the pattern space Print up
to and including the first newline in the pattern
space.
The P and D functions are equivalent to their lower-case
counterparts if there are no imbedded newlines in the pat-
tern space.

3.5. Hold and Get Functions


Four functions save and retrieve part of the input for pos-
sible later use.
(2)h -- hold pattern space The h functions copies the
contents of the pattern space into a hold area
(destroying the previous contents of the hold
area).
(2)H -- Hold pattern space The H function appends the
contents of the pattern space to the contents of
the hold area; the former and new contents are
separated by a newline.
(2)g -- get contents of hold area The g function copies
the contents of the hold area into the pattern
space (destroying the previous contents of the
pattern space).
(2)G -- Get contents of hold area The G function
appends the contents of the hold area to the con-
tents of the pattern space; the former and new
contents are separated by a newline.
(2)x -- exchange The exchange command interchanges the
contents of the pattern space and the hold area.

Example

The commands
1h
1s/ did.*//
1x
G
s/\n/ :/
applied to our standard example, produce:
In Xanadu did Kubla Khan :In Xanadu
A stately pleasure dome decree: :In Xanadu
Where Alph, the sacred river, ran :In Xanadu
Through caverns measureless to man :In Xanadu
Down to a sunless sea. :In Xanadu

3.6. Flow-of-Control Functions


These functions do no editing on the input lines, but con-
trol the application of functions to the lines selected by
the address part.
(2)! -- Don't The Don't command causes the next command
(written on the same line), to be applied to all
and only those input lines not selected by the
adress part.
(2){ -- Grouping The grouping command `{' causes the
next set of commands to be applied (or not
applied) as a block to the input lines selected by
the addresses of the grouping command. The first
of the commands under control of the grouping may
appear on the same line as the `{' or on the next
line.

The group of commands is terminated by a matching
`}' standing on a line by itself.

Groups can be nested.
(0):<label> -- place a label The label function marks a
place in the list of editing commands which may be
referred to by b and t functions. The <label> may
be any sequence of eight or fewer characters; if
two different colon functions have identical
labels, a compile time diagnostic will be gen-
erated, and no execution attempted.
(2)b<label> -- branch to label The branch function
causes the sequence of editing commands being
applied to the current input line to be restarted
immediately after the place where a colon function
with the same <label> was encountered. If no
colon function with the same label can be found
after all the editing commands have been compiled,
a compile time diagnostic is produced, and no exe-
cution is attempted. A b function with no <label>
is taken to be a branch to the end of the list of
editing commands; whatever should be done with the
current input line is done, and another input line
is read; the list of editing commands is restarted
from the beginning on the new line.
(2)t<label> -- test substitutions The t function tests
whether any successful substitutions have been
made on the current input line; if so, it branches
to <label>; if not, it does nothing. The flag
which indicates that a successful substitution has
been executed is reset by:
1) reading a new input line, or
2) executing a t function.

3.7. Miscellaneous Functions


(1)= -- equals The = function writes to the standard
output the line number of the line matched by its
address.
(1)q -- quit The q function causes the current line to
be written to the output (if it should be), any
appended or read text to be written, and execution
to be terminated.


Reference

[1] Ken Thompson and Dennis M. Ritchie, The UNIX
Programmer's Manual. Bell Laboratories, 1978.

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