Invocation
**********
   SED may be invoked with the following command-line options:

`-V'
`--version'
     Print out the version of SED that is being run and a copyright 
     notice, then exit.

`-h'
`--help'
     Print a usage message briefly summarizing these command-line options and
     the bug-reporting address, then exit.

`-n' `--quiet' `--silent'
     By default, SED will print out the pattern space at then end of each cycle
     through the script. These options disable this automatic printing, and SED 
     will only produce output when explicitly told to via the `p' command.

`-e SCRIPT' `--expression=SCRIPT'
     Add the commands in SCRIPT to the set of commands to be run while
     processing the input.

`-f SCRIPT-FILE' `--file=SCRIPT-FILE'
     Add the commands contained in the file SCRIPT-FILE to the set of commands
     to be run while processing the input.

   If no `-e', `-f', `--expression', or `--file' options are given on the command-line, then the first non-option argument on the command line is taken to be the SCRIPT to be executed.

   If any command-line parameters remain after processing the above, these parameters are interpreted as the names of input files to be processed.  A file name of `-' refers to the standard input stream. The standard input will processed if no file names are specified.

SED Programs
************

   A SED program consists of one or more SED commands, passed in by one or more of the `-e', `-f', `--expression', and `--file' options, or the first non-option argument if zero of these options are used. This document will refer to "the" SED script; this will be understood to mean the in-order catenation of all of the SCRIPTs and SCRIPT-FILEs passed in.

   Each SED command consists of an optional address or address range,
followed by a one-character command name and any additional
command-specific code.

Selecting lines with SED
========================

   Addresses in a SED script can be in any of the following forms:
`NUMBER'
     Specifying a line number will match only that line in the input.
     (Note that SED counts lines continuously across all input files.)

`FIRST~STEP'
     This GNU extension matches every STEPth line starting with line
     FIRST.  In particular, lines will be selected when there exists a
     non-negative N such that the current line-number equals FIRST + (N
     * STEP).  Thus, to select the odd-numbered lines, one would use
     `1~2'; to pick every third line starting with the second, `2~3'
     would be used; to pick every fifth line starting with the tenth,
     use `10~5'; and `50~0' is just an obscure way of saying `50'.

`$'  This address matches the last line of the last file of input.

`/REGEXP/'
     This will select any line which matches the regular expression
     REGEXP.  If REGEXP itself includes any `/' characters, each must be
     escaped by a backslash (`\').

`\%REGEXP%' (The `%' may be replaced by any other single character.)

     This also matches the regular expression REGEXP, but allows one to
     use a different delimiter than `/'.  This is particularly useful
     if the REGEXP itself contains a lot of `/'s, since it avoids the
     tedious escaping of every `/'.  If REGEXP itself includes any
     delimiter characters, each must be escaped by a backslash (`\').

`/REGEXP/I' `\%REGEXP%I'
     The `I' modifier to regular-expression matching is a GNU extension
     which causes the REGEXP to be matched in a case-insensitive manner.

   If no addresses are given, then all lines are matched; if one 
address is given, then only lines matching that address are matched.

   An address range can be specified by specifying two addresses
separated by a comma (`,').  An address range matches lines starting
from where the first address matches, and continues until the second
address matches (inclusively).  If the second address is a REGEXP, then
checking for the ending match will start with the line *following* the
line which matched the first address.  If the second address is a
NUMBER less than (or equal to) the line matching the first address,
then only the one line is matched.

   Appending the `!' character to the end of an address specification
will negate the sense of the match.  That is, if the `!' character
follows an address range, then only lines which do *not* match the
address range will be selected.  This also works for singleton
addresses, and, perhaps perversely, for the null address.

Where SED buffers data
======================

   SED maintains two data buffers: the active *pattern* space, and the
auxiliary *hold* space.  In "normal" operation, SED reads in one line
from the input stream and places it in the pattern space.  This pattern
space is where text manipulations occur.  The hold space is initially
empty, but there are commands for moving data between the pattern and
hold spaces.

Often used commands
===================

   If you use SED at all, you will quite likely want to know these
commands.

`#'[No addresses allowed.]

     The `#' "command" begins a comment; the comment continues until
     the next newline.

     If you are concerned about portability, be aware that some
     implementations of SED (which are not POSIX.2 conformant) may only
     support a single one-line comment, and then only when the very
     first character of the script is a `#'.

     Warning: if the first two characters of the SED script are `#n',
     then the `-n' (no-autoprint) option is forced.  If you want to put
     a comment in the first line of your script and that comment begins
     with the letter `n' and you do not want this behavior, then be
     sure to either use a capital `N', or place at least one space
     before the `n'.

`s/REGEXP/REPLACEMENT/FLAGS'
     (The `/' characters may be uniformly replaced by any other single
     character within any given `s' command.)

     The `/' character (or whatever other character is used in its
     stead) can appear in the REGEXP or REPLACEMENT only if it is
     preceded by a `\' character.  Also newlines may appear in the
     REGEXP using the two character sequence `\n'.

     The `s' command attempts to match the pattern space against the
     supplied REGEXP.  If the match is successful, then that portion of
     the pattern space which was matched is replaced with REPLACEMENT.

     The REPLACEMENT can contain `\N' (N being a number from 1 to 9,
     inclusive) references, which refer to the portion of the match
     which is contained between the Nth `\(' and its matching `\)'.
     Also, the REPLACEMENT can contain unescaped `&' characters which
     will reference the whole matched portion of the pattern space.  To
     include a literal `\', `&', or newline in the final replacement,
     be sure to precede the desired `\', `&', or newline in the
     REPLACEMENT with a `\'.

     The `s' command can be followed with zero or more of the following
     FLAGS:

    `g'   Apply the replacement to *all* matches to the REGEXP, not
          just the first.

    `p'   If the substitution was made, then print the new pattern
          space.

    `NUMBER' Only replace the NUMBERth match of the REGEXP.

    `w FILE-NAME'
          If the substitution was made, then write out the result to
          the named file.

    `I'
          (This is a GNU extension.)

          Match REGEXP in a case-insensitive manner.

`q' [At most one address allowed.]

     Exit SED without processing any more commands or input.  Note that
     the current pattern space is printed if auto-print is not disabled.

`d'  Delete the pattern space; immediately start next cycle.

`p'  Print out the pattern space (to the standard output).  This
     command is usually only used in conjunction with the `-n'
     command-line option.

     Note: some implementations of SED, such as this one, will
     double-print lines when auto-print is not disabled and the `p'
     command is given.  Other implementations will only print the line
     once.  Both ways conform with the POSIX.2 standard, and so neither
     way can be considered to be in error.  Portable SED scripts should
     thus avoid relying on either behavior; either use the `-n' option
     and explicitly print what you want, or avoid use of the `p'
     command (and also the `p' flag to the `s' command).

`n'  If auto-print is not disabled, print the pattern space, then,
     regardless, replace the pattern space with the next line of input.
     If there is no more input then SED exits without processing any
     more commands.

`{ COMMANDS }'
     A group of commands may be enclosed between `{' and `}' characters.
     (The `}' must appear in a zero-address command context.)  This is
     particularly useful when you want a group of commands to be
     triggered by a single address (or address-range) match.

Less frequently used commands
=============================

   Though perhaps less frequently used than those in the previous
section, some very small yet useful SED scripts can be built with these
commands.

`y/SOURCE-CHARS/DEST-CHARS/'
     (The `/' characters may be uniformly replaced by any other single
     character within any given `y' command.)

     Transliterate any characters in the pattern space which match any
     of the SOURCE-CHARS with the corresponding character in DEST-CHARS.

     Instances of the `/' (or whatever other character is used in its
     stead), `\', or newlines can appear in the SOURCE-CHARS or
     DEST-CHARS lists, provide that each instance is escaped by a `\'.
     The SOURCE-CHARS and DEST-CHARS lists *must* contain the same
     number of characters (after de-escaping).

`a\'
`TEXT'
     [At most one address allowed.]
     Queue the lines of text which follow this command (each but the
     last ending with a `\', which will be removed from the output) to
     be output at the end of the current cycle, or when the next input
     line is read.

`i\'
`TEXT'
     [At most one address allowed.]
     Immediately output the lines of text which follow this command
     (each but the last ending with a `\', which will be removed from
     the output).

`c\'
`TEXT'
     Delete the lines matching the address or address-range, and output
     the lines of text which follow this command (each but the last
     ending with a `\', which will be removed from the output) in place
     of the last line (or in place of each line, if no addresses were
     specified).  A new cycle is started after this command is done,
     since the pattern space will have been deleted.

`='  [At most one address allowed.]
     Print out the current input line number (with a trailing newline).

`l'  Print the pattern space in an unambiguous form: non-printable
     characters (and the `\' character) are printed in C-style escaped
     form; long lines are split, with a trailing `\' character to
     indicate the split; the end of each line is marked with a `$'.

`r FILENAME' [At most one address allowed.]
     Queue the contents of FILENAME to be read and inserted into the
     output stream at the end of the current cycle, or when the next
     input line is read.  Note that if FILENAME cannot be read, it is
     treated as if it were an empty file, without any error indication.

`w FILENAME'
     Write the pattern space to FILENAME.  The FILENAME will be created
     (or truncated) before the first input line is read; all `w'
     commands (including instances of `w' flag on successful `s'
     commands) which refer to the same FILENAME are output through the
     same FILE stream.

`D'  Delete text in the pattern space up to the first newline.  If any
     text is left, restart cycle with the resultant pattern space
     (without reading a new line of input), otherwise start a normal
     new cycle.

`N'  Add a newline to the pattern space, then append the next line of
     input to the pattern space.  If there is no more input then SED
     exits without processing any more commands.

`P'  Print out the portion of the pattern space up to the first newline.

`h'  Replace the contents of the hold space with the contents of the
     pattern space.

`H'  Append a newline to the contents of the hold space, and then
     append the contents of the pattern space to that of the hold space.

`g'  Replace the contents of the pattern space with the contents of the
     hold space.

`G'  Append a newline to the contents of the pattern space, and then
     append the contents of the hold space to that of the pattern space.

`x'  Exchange the contents of the hold and pattern spaces.

Commands for die-hard SED programmers
=====================================

   In most cases, use of these commands indicates that you are probably
better off programming in something like PERL.  But occasionally one is
committed to sticking with SED, and these commands can enable one to
write quite convoluted scripts.

`: LABEL'
     [No addresses allowed.]
     Specify the location of LABEL for the `b' and `t' commands.  In
     all other respects, a no-op.

`b LABEL'
     Unconditionally branch to LABEL.  The LABEL may be omitted, in
     which case the next cycle is started.

`t LABEL'
     Branch to LABEL only if there has been a successful `s'ubstitution
     since the last input line was read or `t' branch was taken.  The
     LABEL may be omitted, in which case the next cycle is started.