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 space.

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:

[address[,address]]

The sed utility shall support the BREs described in the Base Definitions volume of IEEE Std 1003.1-2001, 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.

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 backslashes 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 optional rfile (or wfile) parameter, separated from the command verb letter or flag by one or more <blank>s; 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.

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

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

[2addr] {function

function

...

}

Execute a list of sed functions only when the pattern space is selected. The list of sed functions shall be surrounded by braces and separated by <newline>s, and conform to the following rules. The braces can be preceded or followed by <blank>s. The functions can be preceded by <blank>s, but shall not be followed by <blank>s. The <right-brace> shall be preceded by a <newline> and can be preceded or followed by <blank>s.

[1addr]a\

text

Write text to standard output as described previously.

[2addr]b [label]

Branch to the : function bearing the label. If label is not specified, branch to the end of the script. The implementation shall support labels recognized as unique up to at least 8 characters; the actual length (greater than or equal to 8) that shall be supported by the implementation is unspecified. It is unspecified whether exceeding a label length causes an error or a silent truncation.

[2addr]c\

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

Delete the initial segment of the pattern space through the first <newline> and start the next cycle.

[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.

[1addr]i\

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 IEEE Std 1003.1-2001, 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 first). If the size of a byte on the system is greater than 9 bits, the format used for non-printable characters is implementation-defined.

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 changes.

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.

[2addr]s/BRE/replacement/flags

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 backreference expression. 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). The meaning of a '\' immediately followed by any character other than '&' , '\' , a digit, or the delimiter character used for this command, is unspecified.

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. 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>s. 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.

[2addr]y/string1/string2/

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.

[0addr]:label

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.