BreadCrumbs: Sed Command

Sed Command

From Luke Jackson

Revision as of 22:41, 2 December 2008; Ljackson (Talk | contribs)
(diff) ←Older revision | Current revision | Newer revision→ (diff)
Jump to: navigation, search

Summary

SED(1) BSD General Commands Manual SED(1)

NAME

    sed -- stream editor

SYNOPSIS

    sed [-Ean] command [file ...]
    sed [-Ean] [-e command] [-f command_file] [-i extension] [file ...]

DESCRIPTION

    The sed utility reads the specified files, or the standard input if no
    files are specified, modifying the input as specified by a list of com-
    mands.  The input is then written to the standard output.
    A single command may be specified as the first argument to sed.  Multiple
    commands may be specified by using the -e or -f options.  All commands
    are applied to the input in the order they are specified regardless of
    their origin.
    The following options are available:
    -E      Interpret regular expressions as extended (modern) regular
            expressions rather than basic regular expressions (BRE's).  The
            re_format(7) manual page fully describes both formats.
    -a      The files listed as parameters for the ``w functions are cre-
            ated (or truncated) before any processing begins, by default.
            The -a option causes sed to delay opening each file until a com-
            mand containing the related ``w function is applied to a line
            of input.
    -e command
            Append the editing commands specified by the command argument to
            the list of commands.
    -f command_file
            Append the editing commands found in the file command_file to the
            list of commands.  The editing commands should each be listed on
            a separate line.
    -i extension
            Edit files in-place, saving backups with the specified extension.
            If a zero-length extension is given, no backup will be saved.  It
            is not recommended to give a zero-length extension when in-place
            editing files, as you risk corruption or partial content in situ-
            ations where disk space is exhausted, etc.
    -n      By default, each line of input is echoed to the standard output
            after all of the commands have been applied to it.  The -n option
            suppresses this behavior.
    The form of a sed command is as follows:
          [address[,address]]function[arguments]
    Whitespace may be inserted before the first address and the function por-
    tions of the command.
    Normally, sed cyclically copies a line of input, not including its termi-
    nating newline character, into a pattern space, (unless there is some-
    thing left after a ``D function), applies all of the commands with
    addresses that select that pattern space, copies the pattern space to the
    standard output, appending a newline, and deletes the pattern space.
    Some of the functions use a hold space to save all or part of the pattern
    space for subsequent retrieval.

Sed Addresses

    An address is not required, but if specified must be a number (that
    counts input lines cumulatively across input files), a dollar (``$)
    character that addresses the last line of input, or a context address
    (which consists of a regular expression preceded and followed by a delim-
    iter).
    A command line with no addresses selects every pattern space.
    A command line with one address selects all of the pattern spaces that
    match the address.
    A command line with two addresses selects an inclusive range.  This range
    starts with the first pattern space that matches the first address.  The
    end of the range is the next following pattern space that matches the
    second address.  If the second address is a number less than or equal to
    the line number first selected, only that line is selected.  In the case
    when the second address is a context address, sed does not re-match the
    second address against the pattern space that matched the first address.
    Starting at the first line following the selected range, sed starts look-
    ing again for the first address.
    Editing commands can be applied to non-selected pattern spaces by use of
    the exclamation character (``!) function.

Sed Regular Expressions

    The regular expressions used in sed, by default, are basic regular
    expressions (BREs, see re_format(7) for more information), but extended
    (modern) regular expressions can be used instead if the -E flag is given.
    In addition, sed has the following two additions to regular expressions:
    1.   In a context address, any character other than a backslash (``\)
         or newline character may be used to delimit the regular expression.
         Also, putting a backslash character before the delimiting character
         causes the character to be treated literally.  For example, in the
         context address \xabc\xdefx, the RE delimiter is an ``x and the
         second ``x stands for itself, so that the regular expression is
         ``abcxdef.
    2.   The escape sequence \n matches a newline character embedded in the
         pattern space.  You can't, however, use a literal newline character
         in an address or in the substitute command.
    One special feature of sed regular expressions is that they can default
    to the last regular expression used.  If a regular expression is empty,
    i.e., just the delimiter characters are specified, the last regular
    expression encountered is used instead.  The last regular expression is
    defined as the last regular expression used as part of an address or sub-
    stitute command, and at run-time, not compile-time.  For example, the
    command ``/abc/s//XXX/ will substitute ``XXX for the pattern ``abc.

Sed Functions

    In the following list of commands, the maximum number of permissible
    addresses for each command is indicated by [0addr], [1addr], or [2addr],
    representing zero, one, or two addresses.
    The argument text consists of one or more lines.  To embed a newline in
    the text, precede it with a backslash.  Other backslashes in text are
    deleted and the following character taken literally.
    The ``r and ``w functions take an optional file parameter, which
    should be separated from the function letter by white space.  Each file
    given as an argument to sed is created (or its contents truncated) before
    any input processing begins.
    The ``b, ``r, ``s, ``t, ``w, ``y, ``!, and ``: functions
    all accept additional arguments.  The following synopses indicate which
    arguments have to be separated from the function letters by white space
    characters.
    Two of the functions take a function-list.  This is a list of sed func-
    tions separated by newlines, as follows:
          { function
            function
            ...
            function
          }
    The ``{ can be preceded by white space and can be followed by white
    space.  The function can be preceded by white space.  The terminating
    ``} must be preceded by a newline or optional white space.
    [2addr] function-list
            Execute function-list only when the pattern space is selected.
    [1addr]a\
    text    Write text to standard output immediately before each attempt to
            read a line of input, whether by executing the ``N function or
            by beginning a new cycle.
    [2addr]b[label]
            Branch to the ``: function with the specified label.  If the
            label is not specified, branch to the end of the script.
    [2addr]c\
    text    Delete the pattern space.  With 0 or 1 address or at the end of a
            2-address range, text is written to the standard output.
    [2addr]d
            Delete the pattern space and start the next cycle.
    [2addr]D
            Delete the initial segment of the pattern space through the first
            newline character and start the next cycle.
    [2addr]g
            Replace the contents of the pattern space with the contents of
            the hold space.
    [2addr]G
            Append a newline character followed by the contents of the hold
            space to the pattern space.
    [2addr]h
            Replace the contents of the hold space with the contents of the
            pattern space.
    [2addr]H
            Append a newline character followed by the contents of the pat-
            tern space to the hold space.
    [1addr]i\
    text    Write text to the standard output.
    [2addr]l
            (The letter ell.)  Write the pattern space to the standard output
            in a visually unambiguous form.  This form is as follows:
                  backslash          \\
                  alert              \a
                  form-feed          \f
                  carriage-return    \r
                  tab                \t
                  vertical tab       \v
            Nonprintable characters are written as three-digit octal numbers
            (with a preceding backslash) for each byte in the character (most
            significant byte first).  Long lines are folded, with the point
            of folding indicated by displaying a backslash followed by a new-
            line.  The end of each line is marked with a ``$.
    [2addr]n
            Write the pattern space to the standard output if the default
            output has not been suppressed, and replace the pattern space
            with the next line of input.
    [2addr]N
            Append the next line of input to the pattern space, using an
            embedded newline character to separate the appended material from
            the original contents.  Note that the current line number
            changes.
    [2addr]p
            Write the pattern space to standard output.
    [2addr]P
            Write the pattern space, up to the first newline character to the
            standard output.
    [1addr]q
            Branch to the end of the script and quit without starting a new
            cycle.
    [1addr]r file
            Copy the contents of file to the standard output immediately
            before the next attempt to read a line of input.  If file cannot
            be read for any reason, it is silently ignored and no error con-
            dition is set.
    [2addr]s/regular expression/replacement/flags
            Substitute the replacement string for the first instance of the
            regular expression in the pattern space.  Any character other
            than backslash or newline can be used instead of a slash to
            delimit the RE and the replacement.  Within the RE and the
            replacement, the RE delimiter itself can be used as a literal
            character if it is preceded by a backslash.
            An ampersand (``&) appearing in the replacement is replaced by
            the string matching the RE.  The special meaning of ``& in this
            context can be suppressed by preceding it by a backslash.  The
            string ``\#, where ``# is a digit, is replaced by the text
            matched by the corresponding backreference expression (see
            re_format(7)).
            A line can be split by substituting a newline character into it.
            To specify a newline character in the replacement string, precede
            it with a backslash.
            The value of flags in the substitute function is zero or more of
            the following:
                  N       Make the substitution only for the N'th occurrence
                          of the regular expression in the pattern space.
                  g       Make the substitution for all non-overlapping
                          matches of the regular expression, not just the
                          first one.
                  p       Write the pattern space to standard output if a
                          replacement was made.  If the replacement string is
                          identical to that which it replaces, it is still
                          considered to have been a replacement.
                  w file  Append the pattern space to file if a replacement
                          was made.  If the replacement string is identical
                          to that which it replaces, it is still considered
                          to have been a replacement.
    [2addr]t [label]
            Branch to the ``: function bearing the label if any substitu-
            tions have been made since the most recent reading of an input
            line or execution of a ``t function.  If no label is specified,
            branch to the end of the script.
    [2addr]w file
            Append the pattern space to the file.
    [2addr]x
            Swap the contents of the pattern and hold spaces.
    [2addr]y/string1/string2/
            Replace all occurrences of characters in string1 in the pattern
            space with the corresponding characters from string2.  Any char-
            acter other than a backslash or newline can be used instead of a
            slash to delimit the strings.  Within string1 and string2, a
            backslash followed by any character other than a newline is that
            literal character, and a backslash followed by an ``n is
            replaced by a newline character.
    [2addr]!function
    [2addr]!function-list
            Apply the function or function-list only to the lines that are
            not selected by the address(es).
    [0addr]:label
            This function does nothing; it bears a label to which the ``b
            and ``t commands may branch.
    [1addr]=
            Write the line number to the standard output followed by a new-
            line character.
    [0addr]
            Empty lines are ignored.
    [0addr]#
            The ``# and the remainder of the line are ignored (treated as a
            comment), with the single exception that if the first two charac-
            ters in the file are ``#n, the default output is suppressed.
            This is the same as specifying the -n option on the command line.

ENVIRONMENT

    The COLUMNS, LANG, LC_ALL, LC_CTYPE and LC_COLLATE environment variables
    affect the execution of sed as described in environ(7).

DIAGNOSTICS

    The sed utility exits 0 on success, and >0 if an error occurs.

SEE ALSO

    awk(1), ed(1), grep(1), regex(3), re_format(7)

STANDARDS

    The sed utility is expected to be a superset of the IEEE Std 1003.2
    (``POSIX.2) specification.
    The -E, -a and -i options are non-standard FreeBSD extensions and may not
    be available on other operating systems.

HISTORY

    A sed command, written by L. E. McMahon, appeared in Version 7 AT&T UNIX.

AUTHORS

    Diomidis D. Spinellis <dds@FreeBSD.org>

BSD July 17, 2004 BSD

Examples

Remove all characters except digits. Replace all characters except digits with null.:

echo "m31uk3_1184329500.jpg" | sed 's/[^[:digit:]]//g'

Trim leading and trailing white space characters:

sed 's/^ *//;s/ *$//'
Personal tools