sed(1p) — Linux manual page


SED(1P)                 POSIX Programmer's Manual                SED(1P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME         top

       sed — stream editor

SYNOPSIS         top

       sed [-n] script [file...]

       sed [-n] -e script [-e script]... [-f script_file]... [file...]

       sed [-n] [-e script]... -f script_file [-f script_file]... [file...]

DESCRIPTION         top

       The sed utility is a stream editor that shall read one or more
       text files, make editing changes according to a script of editing
       commands, and write the results to standard output. The script
       shall be obtained from either the script operand string or a
       combination of the option-arguments from the -e script and -f
       script_file options.

OPTIONS         top

       The sed utility shall conform to the Base Definitions volume of
       POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines, except
       that the order of presentation of the -e and -f options is

       The following options shall be supported:

       -e script Add the editing commands specified by the script
                 option-argument to the end of the script of editing

       -f script_file
                 Add the editing commands in the file script_file to the
                 end of the script of editing commands.

       -n        Suppress the default output (in which each line, after
                 it is examined for editing, is written to standard
                 output). Only lines explicitly selected for output are

       If any -e or -f options are specified, the script of editing
       commands shall initially be empty. The commands specified by each
       -e or -f option shall be added to the script in the order
       specified. When each addition is made, if the previous addition
       (if any) was from a -e option, a <newline> shall be inserted
       before the new addition. The resulting script shall have the same
       properties as the script operand, described in the OPERANDS

OPERANDS         top

       The following operands shall be supported:

       file      A pathname of a file whose contents are read and
                 edited. If multiple file operands are specified, the
                 named files shall be read in the order specified and
                 the concatenation shall be edited. If no file operands
                 are specified, the standard input shall be used.

       script    A string to be used as the script of editing commands.
                 The application shall not present a script that
                 violates the restrictions of a text file except that
                 the final character need not be a <newline>.

STDIN         top

       The standard input shall be used if no file operands are
       specified, and shall be used if a file operand is '-' and the
       implementation treats the '-' as meaning standard input.
       Otherwise, the standard input shall not be used.  See the INPUT
       FILES section.

INPUT FILES         top

       The input files shall be text files. The script_files named by
       the -f option shall consist of editing commands.


       The following environment variables shall affect the execution of

       LANG      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base
                 Definitions volume of POSIX.1‐2017, Section 8.2,
                 Internationalization Variables for the precedence of
                 internationalization variables used to determine the
                 values of locale categories.)

       LC_ALL    If set to a non-empty string value, override the values
                 of all the other internationalization variables.

                 Determine the locale for the behavior of ranges,
                 equivalence classes, and multi-character collating
                 elements within regular expressions.

       LC_CTYPE  Determine the locale for the interpretation of
                 sequences of bytes of text data as characters (for
                 example, single-byte as opposed to multi-byte
                 characters in arguments and input files), and the
                 behavior of character classes within regular

                 Determine the locale that should be used to affect the
                 format and contents of diagnostic messages written to
                 standard error.

       NLSPATH   Determine the location of message catalogs for the
                 processing of LC_MESSAGES.



STDOUT         top

       The input files shall be written to standard output, with the
       editing commands specified in the script applied. If the -n
       option is specified, only those input lines selected by the
       script shall be written to standard output.

STDERR         top

       The standard error shall be used only for diagnostic and warning

OUTPUT FILES         top

       The output files shall be text files whose formats are dependent
       on the editing commands given.


       The script shall consist of editing commands of the following


       where function represents a single-character command verb from
       the list in Editing Commands in sed, followed by any applicable

       The command can be preceded by <blank> characters and/or
       <semicolon> characters. The function can be preceded by <blank>
       characters. These optional characters shall have no effect.

       In default operation, sed cyclically shall append a line of
       input, less its terminating <newline> character, into the pattern
       space. Reading from input shall be skipped if a <newline> was in
       the pattern space prior to a D command ending the previous cycle.
       The sed utility shall then apply in sequence all commands whose
       addresses select that pattern space, until a command starts the
       next cycle or quits. If no commands explicitly started a new
       cycle, then at the end of the script the pattern space shall be
       copied to standard output (except when -n is specified) and the
       pattern space shall be deleted. Whenever the pattern space is
       written to standard output or a named file, sed shall immediately
       follow it with a <newline>.

       Some of the editing commands use a hold space to save all or part
       of the pattern space for subsequent retrieval. The pattern and
       hold spaces shall each be able to hold at least 8192 bytes.

   Addresses in sed
       An address is either a decimal number that counts input lines
       cumulatively across files, a '$' character that addresses the
       last line of input, or a context address (which consists of a
       BRE, as described in Regular Expressions in sed, preceded and
       followed by a delimiter, usually a <slash>).

       An editing command with no addresses shall select every pattern

       An editing command with one address shall select each pattern
       space that matches the address.

       An editing command with two addresses shall select the inclusive
       range from the first pattern space that matches the first address
       through the next pattern space that matches the second. (If the
       second address is a number less than or equal to the line number
       first selected, only one line shall be selected.) Starting at the
       first line following the selected range, sed shall look again for
       the first address. Thereafter, the process shall be repeated.
       Omitting either or both of the address components in the
       following form produces undefined results:


   Regular Expressions in sed
       The sed utility shall support the BREs described in the Base
       Definitions volume of POSIX.1‐2017, Section 9.3, Basic Regular
       Expressions, with the following additions:

        *  In a context address, the construction "\cBREc", where c is
           any character other than <backslash> or <newline>, shall be
           identical to "/BRE/".  If the character designated by c
           appears following a <backslash>, then it shall be considered
           to be that literal character, which shall not terminate the
           BRE. For example, in the context address "\xabc\xdefx", the
           second x stands for itself, so that the BRE is "abcxdef".

        *  The escape sequence '\n' shall match a <newline> embedded in
           the pattern space. A literal <newline> shall not be used in
           the BRE of a context address or in the substitute function.

        *  If an RE is empty (that is, no pattern is specified) sed
           shall behave as if the last RE used in the last command
           applied (either as an address or as part of a substitute
           command) was specified.

   Editing Commands in sed
       In the following list of editing commands, the maximum number of
       permissible addresses for each function is indicated by [0addr],
       [1addr], or [2addr], representing zero, one, or two addresses.

       The argument text shall consist of one or more lines. Each
       embedded <newline> in the text shall be preceded by a
       <backslash>.  Other <backslash> characters in text shall be
       removed, and the following character shall be treated literally.

       The r and w command verbs, and the w flag to the s command, take
       an rfile (or wfile) parameter, separated from the command verb
       letter or flag by one or more <blank> characters; implementations
       may allow zero separation as an extension.

       The argument rfile or the argument wfile shall terminate the
       editing command. Each wfile shall be created before processing
       begins. Implementations shall support at least ten wfile
       arguments in the script; the actual number (greater than or equal
       to 10) that is supported by the implementation is unspecified.
       The use of the wfile parameter shall cause that file to be
       initially created, if it does not exist, or shall replace the
       contents of an existing file.

       The b, r, s, t, w, y, and : command verbs shall accept additional
       arguments. The following synopses indicate which arguments shall
       be separated from the command verbs by a single <space>.

       The a and r commands schedule text for later output. The text
       specified for the a command, and the contents of the file
       specified for the r command, shall be written to standard output
       just before the next attempt to fetch a line of input when
       executing the N or n commands, or when reaching the end of the
       script. If written when reaching the end of the script, and the
       -n option was not specified, the text shall be written after
       copying the pattern space to standard output. The contents of the
       file specified for the r command shall be as of the time the
       output is written, not the time the r command is applied. The
       text shall be output in the order in which the a and r commands
       were applied to the input.

       Editing commands other than {...}, a, b, c, i, r, t, w, :, and #
       can be followed by a <semicolon>, optional <blank> characters,
       and another editing command. However, when an s editing command
       is used with the w flag, following it with another command in
       this manner produces undefined results.

       A function can be preceded by a '!'  character, in which case the
       function shall be applied if the addresses do not select the
       pattern space. Zero or more <blank> characters shall be accepted
       before the '!'  character. It is unspecified whether <blank>
       characters can follow the '!'  character, and conforming
       applications shall not follow the '!'  character with <blank>

       If a label argument (to a b, t, or : command) contains characters
       outside of the portable filename character set, or if a label is
       longer than 8 bytes, the behavior is unspecified. The
       implementation shall support label arguments recognized as unique
       up to at least 8 bytes; the actual length (greater than or equal
       to 8) supported by the implementation is unspecified. It is
       unspecified whether exceeding the maximum supported label length
       causes an error or a silent truncation.

       [2addr] {editing command

       editing command


       }         Execute a list of sed editing commands only when the
                 pattern space is selected. The list of sed editing
                 commands shall be surrounded by braces. The braces can
                 be preceded or followed by <blank> characters. The
                 <right-brace> shall be preceded by a <newline> or
                 <semicolon> (before any optional <blank> characters
                 preceding the <right-brace>).

                 Each command in the list of commands shall be
                 terminated by a <newline> character, or by a
                 <semicolon> character if permitted when the command is
                 used outside the braces.  The editing commands can be
                 preceded by <blank> characters, but shall not be
                 followed by <blank> characters.


       text      Write text to standard output as described previously.

       [2addr]b [label]
                 Branch to the : command verb bearing the label
                 argument.  If label is not specified, branch to the end
                 of the script.


       text      Delete the pattern space. With a 0 or 1 address or at
                 the end of a 2-address range, place text on the output
                 and start the next cycle.

       [2addr]d  Delete the pattern space and start the next cycle.

       [2addr]D  If the pattern space contains no <newline>, delete the
                 pattern space and start a normal new cycle as if the d
                 command was issued. Otherwise, delete the initial
                 segment of the pattern space through the first
                 <newline>, and start the next cycle with the resultant
                 pattern space and without reading any new input.

       [2addr]g  Replace the contents of the pattern space by the
                 contents of the hold space.

       [2addr]G  Append to the pattern space a <newline> followed by the
                 contents of the hold space.

       [2addr]h  Replace the contents of the hold space with the
                 contents of the pattern space.

       [2addr]H  Append to the hold space a <newline> followed by the
                 contents of the pattern space.


       text      Write text to standard output.

       [2addr]l  (The letter ell.) Write the pattern space to standard
                 output in a visually unambiguous form. The characters
                 listed in the Base Definitions volume of POSIX.1‐2017,
                 Table 5-1, Escape Sequences and Associated Actions
                 ('\\', '\a', '\b', '\f', '\r', '\t', '\v') shall be
                 written as the corresponding escape sequence; the '\n'
                 in that table is not applicable. Non-printable
                 characters not in that table shall be written as one
                 three-digit octal number (with a preceding <backslash>)
                 for each byte in the character (most significant byte

                 Long lines shall be folded, with the point of folding
                 indicated by writing a <backslash> followed by a
                 <newline>; the length at which folding occurs is
                 unspecified, but should be appropriate for the output
                 device. The end of each line shall be marked with a

       [2addr]n  Write the pattern space to standard output if the
                 default output has not been suppressed, and replace the
                 pattern space with the next line of input, less its
                 terminating <newline>.

                 If no next line of input is available, the n command
                 verb shall branch to the end of the script and quit
                 without starting a new cycle.

       [2addr]N  Append the next line of input, less its terminating
                 <newline>, to the pattern space, using an embedded
                 <newline> to separate the appended material from the
                 original material. Note that the current line number

                 If no next line of input is available, the N command
                 verb shall branch to the end of the script and quit
                 without starting a new cycle or copying the pattern
                 space to standard output.

       [2addr]p  Write the pattern space to standard output.

       [2addr]P  Write the pattern space, up to the first <newline>, to
                 standard output.

       [1addr]q  Branch to the end of the script and quit without
                 starting a new cycle.

       [1addr]r rfile
                 Copy the contents of rfile to standard output as
                 described previously. If rfile does not exist or cannot
                 be read, it shall be treated as if it were an empty
                 file, causing no error condition.

                 Substitute the replacement string for instances of the
                 BRE in the pattern space. Any character other than
                 <backslash> or <newline> can be used instead of a
                 <slash> to delimit the BRE and the replacement. Within
                 the BRE and the replacement, the BRE delimiter itself
                 can be used as a literal character if it is preceded by
                 a <backslash>.

                 The replacement string shall be scanned from beginning
                 to end. An <ampersand> ('&') appearing in the
                 replacement shall be replaced by the string matching
                 the BRE. The special meaning of '&' in this context can
                 be suppressed by preceding it by a <backslash>.  The
                 characters "\n", where n is a digit, shall be replaced
                 by the text matched by the corresponding back-reference
                 expression. If the corresponding back-reference
                 expression does not match, then the characters "\n"
                 shall be replaced by the empty string. The special
                 meaning of "\n" where n is a digit in this context, can
                 be suppressed by preceding it by a <backslash>.  For
                 each other <backslash> encountered, the following
                 character shall lose its special meaning (if any).

                 A line can be split by substituting a <newline> into
                 it. The application shall escape the <newline> in the
                 replacement by preceding it by a <backslash>.

                 The meaning of an unescaped <backslash> immediately
                 followed by any character other than '&', <backslash>,
                 a digit, <newline>, or the delimiter character used for
                 this command, is unspecified.

                 A substitution shall be considered to have been
                 performed even if the replacement string is identical
                 to the string that it replaces. Any <backslash> used to
                 alter the default meaning of a subsequent character
                 shall be discarded from the BRE or the replacement
                 before evaluating the BRE or using the replacement.

                 The value of flags shall be zero or more of:

                 n         Substitute for the nth occurrence only of the
                           BRE found within the pattern space.

                 g         Globally substitute for all non-overlapping
                           instances of the BRE rather than just the
                           first one. If both g and n are specified, the
                           results are unspecified.

                 p         Write the pattern space to standard output if
                           a replacement was made.

                 w wfile   Write. Append the pattern space to wfile if a
                           replacement was made. A conforming
                           application shall precede the wfile argument
                           with one or more <blank> characters. If the w
                           flag is not the last flag value given in a
                           concatenation of multiple flag values, the
                           results are undefined.

       [2addr]t [label]
                 Test. Branch to the : command verb bearing the label if
                 any substitutions have been made since the most recent
                 reading of an input line or execution of a t.  If label
                 is not specified, branch to the end of the script.

       [2addr]w wfile
                 Append (write) the pattern space to wfile.

       [2addr]x  Exchange the contents of the pattern and hold spaces.

                 Replace all occurrences of characters in string1 with
                 the corresponding characters in string2.  If a
                 <backslash> followed by an 'n' appear in string1 or
                 string2, the two characters shall be handled as a
                 single <newline>.  If the number of characters in
                 string1 and string2 are not equal, or if any of the
                 characters in string1 appear more than once, the
                 results are undefined. Any character other than
                 <backslash> or <newline> can be used instead of <slash>
                 to delimit the strings. If the delimiter is not 'n',
                 within string1 and string2, the delimiter itself can be
                 used as a literal character if it is preceded by a
                 <backslash>.  If a <backslash> character is immediately
                 followed by a <backslash> character in string1 or
                 string2, the two <backslash> characters shall be
                 counted as a single literal <backslash> character. The
                 meaning of a <backslash> followed by any character that
                 is not 'n', a <backslash>, or the delimiter character
                 is undefined.

                 Do nothing. This command bears a label to which the b
                 and t commands branch.

       [1addr]=  Write the following to standard output:

                     "%d\n", <current line number>

       [0addr]   Ignore this empty command.

       [0addr]#  Ignore the '#' and the remainder of the line (treat
                 them as a comment), with the single exception that if
                 the first two characters in the script are "#n", the
                 default output shall be suppressed; this shall be the
                 equivalent of specifying -n on the command line.

EXIT STATUS         top

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.



       The following sections are informative.


       Regular expressions match entire strings, not just individual
       lines, but a <newline> is matched by '\n' in a sed RE; a
       <newline> is not allowed by the general definition of regular
       expression in POSIX.1‐2008. Also note that '\n' cannot be used to
       match a <newline> at the end of an arbitrary input line;
       <newline> characters appear in the pattern space as a result of
       the N editing command.

       When using sed to process pathnames, it is recommended that
       LC_ALL, or at least LC_CTYPE and LC_COLLATE, are set to POSIX or
       C in the environment, since pathnames can contain byte sequences
       that do not form valid characters in some locales, in which case
       the utility's behavior would be undefined. In the POSIX locale
       each byte is a valid single-byte character, and therefore this
       problem is avoided.

EXAMPLES         top

       This sed script simulates the BSD cat -s command, squeezing
       excess empty lines from standard input.

           sed -n '
           # Write non-empty lines.
           /./ {
           # Write a single empty line, then look for more empty lines.
           /^$/    p
           # Get next line, discard the held <newline> (empty line),
           # and look for more empty lines.
           /^$/    {
               b Empty
           # Write the non-empty line before going back to search
           # for the first in a set of empty lines.

       The following sed command is a much simpler method of squeezing
       empty lines, although it is not quite the same as cat -s since it
       removes any initial empty lines:

           sed -n '/./,/^$/p'

RATIONALE         top

       This volume of POSIX.1‐2017 requires implementations to support
       at least ten distinct wfiles, matching historical practice on
       many implementations. Implementations are encouraged to support
       more, but conforming applications should not exceed this limit.

       The exit status codes specified here are different from those in
       System V. System V returns 2 for garbled sed commands, but
       returns zero with its usage message or if the input file could
       not be opened. The standard developers considered this to be a

       The manner in which the l command writes non-printable characters
       was changed to avoid the historical backspace-overstrike method,
       and other requirements to achieve unambiguous output were added.
       See the RATIONALE for ed(1p) for details of the format chosen,
       which is the same as that chosen for sed.

       This volume of POSIX.1‐2017 requires implementations to provide
       pattern and hold spaces of at least 8192 bytes, larger than the
       4000 bytes spaces used by some historical implementations, but
       less than the 20480 bytes limit used in an early proposal.
       Implementations are encouraged to allocate dynamically larger
       pattern and hold spaces as needed.

       The requirements for acceptance of <blank> and <space> characters
       in command lines has been made more explicit than in early
       proposals to describe clearly the historical practice and to
       remove confusion about the phrase ``protect initial blanks [sic]
       and tabs from the stripping that is done on every script line''
       that appears in much of the historical documentation of the sed
       utility description of text. (Not all implementations are known
       to have stripped <blank> characters from text lines, although
       they all have allowed leading <blank> characters preceding the
       address on a command line.)

       The treatment of '#' comments differs from the SVID which only
       allows a comment as the first line of the script, but matches
       BSD-derived implementations. The comment character is treated as
       a command, and it has the same properties in terms of being
       accepted with leading <blank> characters; the BSD implementation
       has historically supported this.

       Early proposals required that a script_file have at least one
       non-comment line. Some historical implementations have behaved in
       unexpected ways if this were not the case. The standard
       developers considered that this was incorrect behavior and that
       application developers should not have to avoid this feature. A
       correct implementation of this volume of POSIX.1‐2017 shall
       permit script_files that consist only of comment lines.

       Early proposals indicated that if -e and -f options were
       intermixed, all -e options were processed before any -f options.
       This has been changed to process them in the order presented
       because it matches historical practice and is more intuitive.

       The treatment of the p flag to the s command differs between
       System V and BSD-based systems when the default output is
       suppressed. In the two examples:

           echo a | sed    's/a/A/p'
           echo a | sed -n 's/a/A/p'

       this volume of POSIX.1‐2017, BSD, System V documentation, and the
       SVID indicate that the first example should write two lines with
       A, whereas the second should write one. Some System V systems
       write the A only once in both examples because the p flag is
       ignored if the -n option is not specified.

       This is a case of a diametrical difference between systems that
       could not be reconciled through the compromise of declaring the
       behavior to be unspecified. The SVID/BSD/System V documentation
       behavior was adopted for this volume of POSIX.1‐2017 because:

        *  No known documentation for any historic system describes the
           interaction between the p flag and the -n option.

        *  The selected behavior is more correct as there is no
           technical justification for any interaction between the p
           flag and the -n option. A relationship between -n and the p
           flag might imply that they are only used together, but this
           ignores valid scripts that interrupt the cyclical nature of
           the processing through the use of the D, d, q, or branching
           commands. Such scripts rely on the p suffix to write the
           pattern space because they do not make use of the default
           output at the ``bottom'' of the script.

        *  Because the -n option makes the p flag unnecessary, any
           interaction would only be useful if sed scripts were written
           to run both with and without the -n option. This is believed
           to be unlikely. It is even more unlikely that programmers
           have coded the p flag expecting it to be unnecessary. Because
           the interaction was not documented, the likelihood of a
           programmer discovering the interaction and depending on it is
           further decreased.

        *  Finally, scripts that break under the specified behavior
           produce too much output instead of too little, which is
           easier to diagnose and correct.

       The form of the substitute command that uses the n suffix was
       limited to the first 512 matches in an early proposal. This limit
       has been removed because there is no reason an editor processing
       lines of {LINE_MAX} length should have this restriction. The
       command s/a/A/2047 should be able to substitute the 2047th
       occurrence of a on a line.

       The b, t, and : commands are documented to ignore leading white
       space, but no mention is made of trailing white space. Historical
       implementations of sed assigned different locations to the labels
       'x' and "x ".  This is not useful, and leads to subtle
       programming errors, but it is historical practice, and changing
       it could theoretically break working scripts. Implementors are
       encouraged to provide warning messages about labels that are
       never referenced by a b or t command, jumps to labels that do not
       exist, and label arguments that are subject to truncation.

       Earlier versions of this standard allowed for implementations
       with bytes other than eight bits, but this has been modified in
       this version.



SEE ALSO         top

       awk(1p), ed(1p), grep(1p)

       The Base Definitions volume of POSIX.1‐2017, Table 5-1, Escape
       Sequences and Associated Actions, Chapter 8, Environment
       Variables, Section 9.3, Basic Regular Expressions, Section 12.2,
       Utility Syntax Guidelines

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see .

IEEE/The Open Group               2017                           SED(1P)

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