diff options
Diffstat (limited to 'man-pages-posix-2003/man1p/sed.1p')
| -rw-r--r-- | man-pages-posix-2003/man1p/sed.1p | 738 |
1 files changed, 738 insertions, 0 deletions
diff --git a/man-pages-posix-2003/man1p/sed.1p b/man-pages-posix-2003/man1p/sed.1p new file mode 100644 index 0000000..243e5e7 --- /dev/null +++ b/man-pages-posix-2003/man1p/sed.1p @@ -0,0 +1,738 @@ +.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved +.TH "SED" 1P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual" +.\" sed +.SH PROLOG +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. +.SH NAME +sed \- stream editor +.SH SYNOPSIS +.LP +\fBsed\fP \fB[\fP\fB-n\fP\fB]\fP \fIscript\fP\fB[\fP\fIfile\fP\fB...\fP\fB]\fP\fB +.br +.sp +sed\fP \fB[\fP\fB-n\fP\fB][\fP\fB-e\fP \fIscript\fP\fB]\fP\fB...\fP\fB[\fP\fB-f\fP +\fIscript_file\fP\fB]\fP\fB...\fP\fB[\fP\fIfile\fP\fB...\fP\fB]\fP\fB +.br +\fP +.SH DESCRIPTION +.LP +The \fIsed\fP 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 \fIscript\fP operand +string or a combination of the option-arguments from the \fB-e\fP +\fIscript\fP and \fB-f\fP \fIscript_file\fP options. +.SH OPTIONS +.LP +The \fIsed\fP utility shall conform to the Base Definitions volume +of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines, +except that the order of presentation of the +\fB-e\fP and \fB-f\fP options is significant. +.LP +The following options shall be supported: +.TP 7 +\fB-e\ \fP \fIscript\fP +Add the editing commands specified by the \fIscript\fP option-argument +to the end of the script of editing commands. The +\fIscript\fP option-argument shall have the same properties as the +\fIscript\fP operand, described in the OPERANDS section. +.TP 7 +\fB-f\ \fP \fIscript_file\fP +Add the editing commands in the file \fIscript_file\fP to the end +of the script. +.TP 7 +\fB-n\fP +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 written. +.sp +.LP +Multiple \fB-e\fP and \fB-f\fP options may be specified. All commands +shall be added to the script in the order specified, +regardless of their origin. +.SH OPERANDS +.LP +The following operands shall be supported: +.TP 7 +\fIfile\fP +A pathname of a file whose contents are read and edited. If multiple +\fIfile\fP operands are specified, the named files shall +be read in the order specified and the concatenation shall be edited. +If no \fIfile\fP operands are specified, the standard input +shall be used. +.TP 7 +\fIscript\fP +A string to be used as the script of editing commands. The application +shall not present a \fIscript\fP that violates the +restrictions of a text file except that the final character need not +be a <newline>. +.sp +.SH STDIN +.LP +The standard input shall be used only if no \fIfile\fP operands are +specified. See the INPUT FILES section. +.SH INPUT FILES +.LP +The input files shall be text files. The \fIscript_file\fPs named +by the \fB-f\fP option shall consist of editing +commands. +.SH ENVIRONMENT VARIABLES +.LP +The following environment variables shall affect the execution of +\fIsed\fP: +.TP 7 +\fILANG\fP +Provide a default value for the internationalization variables that +are unset or null. (See the Base Definitions volume of +IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables +for +the precedence of internationalization variables used to determine +the values of locale categories.) +.TP 7 +\fILC_ALL\fP +If set to a non-empty string value, override the values of all the +other internationalization variables. +.TP 7 +\fILC_COLLATE\fP +.sp +Determine the locale for the behavior of ranges, equivalence classes, +and multi-character collating elements within regular +expressions. +.TP 7 +\fILC_CTYPE\fP +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 +expressions. +.TP 7 +\fILC_MESSAGES\fP +Determine the locale that should be used to affect the format and +contents of diagnostic messages written to standard +error. +.TP 7 +\fINLSPATH\fP +Determine the location of message catalogs for the processing of \fILC_MESSAGES +\&.\fP +.sp +.SH ASYNCHRONOUS EVENTS +.LP +Default. +.SH STDOUT +.LP +The input files shall be written to standard output, with the editing +commands specified in the script applied. If the \fB-n\fP +option is specified, only those input lines selected by the script +shall be written to standard output. +.SH STDERR +.LP +The standard error shall be used only for diagnostic messages. +.SH OUTPUT FILES +.LP +The output files shall be text files whose formats are dependent on +the editing commands given. +.SH EXTENDED DESCRIPTION +.LP +The \fIscript\fP shall consist of editing commands of the following +form: +.sp +.RS +.nf + +\fB[\fP\fIaddress\fP\fB[\fP\fB,\fP\fIaddress\fP\fB]]\fP\fIfunction\fP +.fi +.RE +.LP +where \fIfunction\fP represents a single-character command verb from +the list in Editing Commands +in sed, followed by any applicable arguments. +.LP +The command can be preceded by <blank>s and/or semicolons. The function +can be preceded by <blank>s. These optional +characters shall have no effect. +.LP +In default operation, \fIsed\fP cyclically shall append a line of +input, less its terminating <newline>, into the pattern +space. Normally the pattern space will be empty, unless a \fBD\fP +command terminated the last cycle. The \fIsed\fP utility shall +then apply in sequence all commands whose addresses select that pattern +space, and at the end of the script copy the pattern space +to standard output (except when \fB-n\fP is specified) and delete +the pattern space. Whenever the pattern space is written to +standard output or a named file, \fIsed\fP shall immediately follow +it with a <newline>. +.LP +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. +.SS Addresses in sed +.LP +An address is either a decimal number that counts input lines cumulatively +across files, a \fB'$'\fP 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). +.LP +An editing command with no addresses shall select every pattern space. +.LP +An editing command with one address shall select each pattern space +that matches the address. +.LP +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, \fIsed\fP 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: +.sp +.RS +.nf + +\fB[\fP\fIaddress\fP\fB[\fP\fB,\fP\fIaddress\fP\fB]]\fP +.fi +.RE +.SS Regular Expressions in sed +.LP +The \fIsed\fP 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: +.IP " *" 3 +In a context address, the construction \fB"\\cBREc"\fP, where \fIc\fP +is any character other than backslash or +<newline>, shall be identical to \fB"/BRE/"\fP . If the character +designated by \fIc\fP 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 +\fB"\\xabc\\xdefx"\fP, the second \fIx\fP stands for itself, so that +the BRE is \fB"abcxdef"\fP . +.LP +.IP " *" 3 +The escape sequence \fB'\\n'\fP 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. +.LP +.IP " *" 3 +If an RE is empty (that is, no pattern is specified) \fIsed\fP 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. +.LP +.SS Editing Commands in sed +.LP +In the following list of editing commands, the maximum number of permissible +addresses for each function is indicated by [ +\fI0addr\fP], [ \fI1addr\fP], or [ \fI2addr\fP], representing zero, +one, or two addresses. +.LP +The argument \fItext\fP 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. +.LP +The \fBr\fP and \fBw\fP command verbs, and the \fIw\fP flag to the +\fBs\fP command, take an optional \fIrfile\fP (or +\fIwfile\fP) parameter, separated from the command verb letter or +flag by one or more <blank>s; implementations may allow +zero separation as an extension. +.LP +The argument \fIrfile\fP or the argument \fIwfile\fP shall terminate +the editing command. Each \fIwfile\fP shall be created +before processing begins. Implementations shall support at least ten +\fIwfile\fP 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 \fIwfile\fP parameter shall +cause that file to be initially created, if it does not exist, or +shall replace the contents of an existing file. +.LP +The \fBb\fP, \fBr\fP, \fBs\fP, \fBt\fP, \fBw\fP, \fBy\fP, and \fB:\fP +command verbs shall accept additional arguments. +The following synopses indicate which arguments shall be separated +from the command verbs by a single <space>. +.LP +The \fBa\fP and \fBr\fP commands schedule text for later output. The +text specified for the \fBa\fP command, and the contents +of the file specified for the \fBr\fP command, shall be written to +standard output just before the next attempt to fetch a line of +input when executing the \fBN\fP or \fBn\fP commands, or when reaching +the end of the script. If written when reaching the end of +the script, and the \fB-n\fP 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 \fBr\fP command +shall be as of the time the output is written, not the time the +\fBr\fP command is applied. The text shall be output in the order +in which the \fBa\fP and \fBr\fP commands were applied to the +input. +.LP +Command verbs other than \fB{\fP, \fBa\fP, \fBb\fP, \fBc\fP, \fBi\fP, +\fBr\fP, \fBt\fP, \fBw\fP, \fB:\fP, and \fB#\fP +can be followed by a semicolon, optional <blank>s, and another command +verb. However, when the \fBs\fP command verb is used +with the \fIw\fP flag, following it with another command in this manner +produces undefined results. +.LP +A function can be preceded by one or more \fB'!'\fP 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 \fB'!'\fP character. It is +unspecified whether <blank>s can follow a \fB'!'\fP character, and +conforming applications shall not follow a \fB'!'\fP +character with <blank>s. +.TP 7 +\fB[\fP\fI2addr\fP\fB]\ {\fP\fIfunction\fP +.TP 7 +\fIfunction\fP +.TP 7 +\&... +.TP 7 +\fB}\fP +Execute a list of \fIsed\fP functions only when the pattern space +is selected. The list of \fIsed\fP 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. +.TP 7 +\fB[\fP\fI1addr\fP\fB]a\\\fP +.TP 7 +\fItext\fP +Write text to standard output as described previously. +.TP 7 +\fB[\fP\fI2addr\fP\fB]b\ [\fP\fIlabel\fP\fB]\fP +.sp +Branch to the \fB:\fP function bearing the \fIlabel\fP. If \fIlabel\fP +is not specified, branch to the end of the script. The +implementation shall support \fIlabel\fPs 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. +.TP 7 +\fB[\fP\fI2addr\fP\fB]c\\\fP +.TP 7 +\fItext\fP +Delete the pattern space. With a 0 or 1 address or at the end of a +2-address range, place \fItext\fP on the output and start +the next cycle. +.TP 7 +\fB[\fP\fI2addr\fP\fB]d\fP +Delete the pattern space and start the next cycle. +.TP 7 +\fB[\fP\fI2addr\fP\fB]D\fP +Delete the initial segment of the pattern space through the first +<newline> and start the next cycle. +.TP 7 +\fB[\fP\fI2addr\fP\fB]g\fP +Replace the contents of the pattern space by the contents of the hold +space. +.TP 7 +\fB[\fP\fI2addr\fP\fB]G\fP +Append to the pattern space a <newline> followed by the contents of +the hold space. +.TP 7 +\fB[\fP\fI2addr\fP\fB]h\fP +Replace the contents of the hold space with the contents of the pattern +space. +.TP 7 +\fB[\fP\fI2addr\fP\fB]H\fP +Append to the hold space a <newline> followed by the contents of the +pattern space. +.TP 7 +\fB[\fP\fI1addr\fP\fB]i\\\fP +.TP 7 +\fItext\fP +Write \fItext\fP to standard output. +.TP 7 +\fB[\fP\fI2addr\fP\fB]l\fP +(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 ( \fB'\\\\'\fP, +\fB'\\a'\fP, \fB'\\b'\fP, \fB'\\f'\fP, \fB'\\r'\fP, \fB'\\t'\fP, +\fB'\\v'\fP ) shall be written as the +corresponding escape sequence; the \fB'\\n'\fP 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. +.LP +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 \fB'$'\fP . +.TP 7 +\fB[\fP\fI2addr\fP\fB]n\fP +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>. +.LP +If no next line of input is available, the \fBn\fP command verb shall +branch to the end of the script and quit without starting +a new cycle. +.TP 7 +\fB[\fP\fI2addr\fP\fB]N\fP +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. +.LP +If no next line of input is available, the \fBN\fP 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. +.TP 7 +\fB[\fP\fI2addr\fP\fB]p\fP +Write the pattern space to standard output. +.TP 7 +\fB[\fP\fI2addr\fP\fB]P\fP +Write the pattern space, up to the first <newline>, to standard output. +.TP 7 +\fB[\fP\fI1addr\fP\fB]q\fP +Branch to the end of the script and quit without starting a new cycle. +.TP 7 +\fB[\fP\fI1addr\fP\fB]r\ \fP \fIrfile\fP +Copy the contents of \fIrfile\fP to standard output as described previously. +If \fIrfile\fP does not exist or cannot be read, +it shall be treated as if it were an empty file, causing no error +condition. +.TP 7 +\fB[\fP\fI2addr\fP\fB]s/\fP\fIBRE\fP\fB/\fP\fIreplacement\fP\fB/\fP\fIflags\fP +.sp +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. +.LP +The replacement string shall be scanned from beginning to end. An +ampersand ( \fB'&'\fP ) appearing in the replacement +shall be replaced by the string matching the BRE. The special meaning +of \fB'&'\fP in this context can be suppressed by +preceding it by a backslash. The characters \fB"\\\fP\fIn"\fP, where +\fIn\fP is a digit, shall be replaced by the text matched +by the corresponding backreference expression. The special meaning +of \fB"\\\fP\fIn"\fP where \fIn\fP is a digit in this +context, can be suppressed by preceding it by a backslash. For each +other backslash ( \fB'\\'\fP ) encountered, the following +character shall lose its special meaning (if any). The meaning of +a \fB'\\'\fP immediately followed by any character other than +\fB'&'\fP, \fB'\\'\fP, a digit, or the delimiter character used +for this command, is unspecified. +.LP +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. +.LP +The value of \fIflags\fP shall be zero or more of: +.TP 7 +\fIn\fP +.RS +Substitute for the \fIn\fPth occurrence only of the BRE found within +the pattern space. +.RE +.TP 7 +\fBg\fP +.RS +Globally substitute for all non-overlapping instances of the BRE rather +than just the first one. If both \fBg\fP and \fIn\fP +are specified, the results are unspecified. +.RE +.TP 7 +\fBp\fP +.RS +Write the pattern space to standard output if a replacement was made. +.RE +.TP 7 +\fBw\ \fP \fIwfile\fP +.RS +Write. Append the pattern space to \fIwfile\fP if a replacement was +made. A conforming application shall precede the +\fIwfile\fP argument with one or more <blank>s. If the \fBw\fP flag +is not the last flag value given in a concatenation of +multiple flag values, the results are undefined. +.RE +.sp +.TP 7 +\fB[\fP\fI2addr\fP\fB]t\ [\fP\fIlabel\fP\fB]\fP +.sp +Test. Branch to the \fB:\fP command verb bearing the \fIlabel\fP if +any substitutions have been made since the most recent +reading of an input line or execution of a \fBt\fP. If \fIlabel\fP +is not specified, branch to the end of the script. +.TP 7 +\fB[\fP\fI2addr\fP\fB]w\ \fP \fIwfile\fP +.sp +Append (write) the pattern space to \fIwfile\fP. +.TP 7 +\fB[\fP\fI2addr\fP\fB]x\fP +Exchange the contents of the pattern and hold spaces. +.TP 7 +\fB[\fP\fI2addr\fP\fB]y/\fP\fIstring1\fP\fB/\fP\fIstring2\fP\fB/\fP +.sp +Replace all occurrences of characters in \fIstring1\fP with the corresponding +characters in \fIstring2\fP. If a backslash +followed by an \fB'n'\fP appear in \fIstring1\fP or \fIstring2\fP, +the two characters shall be handled as a single +<newline>. If the number of characters in \fIstring1\fP and \fIstring2\fP +are not equal, or if any of the characters in +\fIstring1\fP 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 \fIn\fP, +within \fIstring1\fP and \fIstring2\fP, 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 \fIstring1\fP or \fIstring2\fP, 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 \fB'n'\fP, a backslash, or the delimiter +character is undefined. +.TP 7 +\fB[\fP\fI0addr\fP\fB]:\fP\fIlabel\fP +Do nothing. This command bears a \fIlabel\fP to which the \fBb\fP +and \fBt\fP commands branch. +.TP 7 +\fB[\fP\fI1addr\fP\fB]=\fP +Write the following to standard output: +.sp +.RS +.nf + +\fB"%d\\n", <\fP\fIcurrent line number\fP\fB> +\fP +.fi +.RE +.TP 7 +\fB[\fP\fI0addr\fP\fB]\fP +Ignore this empty command. +.TP 7 +\fB[\fP\fI0addr\fP\fB]#\fP +Ignore the \fB'#'\fP 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 \fB"#n"\fP, the default output shall +be suppressed; this shall be the equivalent of specifying +\fB-n\fP on the command line. +.sp +.SH EXIT STATUS +.LP +The following exit values shall be returned: +.TP 7 +\ 0 +Successful completion. +.TP 7 +>0 +An error occurred. +.sp +.SH CONSEQUENCES OF ERRORS +.LP +Default. +.LP +\fIThe following sections are informative.\fP +.SH APPLICATION USAGE +.LP +Regular expressions match entire strings, not just individual lines, +but a <newline> is matched by \fB'\\n'\fP in a +\fIsed\fP RE; a <newline> is not allowed by the general definition +of regular expression in IEEE\ Std\ 1003.1-2001. +Also note that \fB'\\n'\fP cannot be used to match a <newline> at +the end of an arbitrary input line; <newline>s +appear in the pattern space as a result of the \fBN\fP editing command. +.SH EXAMPLES +.LP +This \fIsed\fP script simulates the BSD \fIcat\fP \fB-s\fP command, +squeezing excess +blank lines from standard input. +.sp +.RS +.nf + +\fBsed -n ' +# Write non-empty lines. +/./ { + p + d + } +# Write a single empty line, then look for more empty lines. +/^$/ p +# Get next line, discard the held <newline> (empty line), +# and look for more empty lines. +:Empty +/^$/ { + N + s/.// + b Empty + } +# Write the non-empty line before going back to search +# for the first in a set of empty lines. + p +' +\fP +.fi +.RE +.SH RATIONALE +.LP +This volume of IEEE\ Std\ 1003.1-2001 requires implementations to +support at least ten distinct \fIwfile\fPs, matching +historical practice on many implementations. Implementations are encouraged +to support more, but conforming applications should not +exceed this limit. +.LP +The exit status codes specified here are different from those in System +V. System V returns 2 for garbled \fIsed\fP 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 +bug. +.LP +The manner in which the \fBl\fP 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 \fIed\fP for details of the +format chosen, which is the same as that chosen for \fIsed\fP. +.LP +This volume of IEEE\ Std\ 1003.1-2001 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. +.LP +The requirements for acceptance of <blank>s and <space>s 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 +[\fIsic\fP] and tabs from the stripping that is done on every script +line" that appears in much of the historical documentation +of the \fIsed\fP utility description of text. (Not all implementations +are known to have stripped <blank>s from text lines, +although they all have allowed leading <blank>s preceding the address +on a command line.) +.LP +The treatment of \fB'#'\fP 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>s; the BSD implementation has historically +supported this. +.LP +Early proposals required that a \fIscript_file\fP 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 +IEEE\ Std\ 1003.1-2001 shall permit \fIscript_file\fPs that consist +only of comment lines. +.LP +Early proposals indicated that if \fB-e\fP and \fB-f\fP options were +intermixed, all \fB-e\fP options were processed before +any \fB-f\fP options. This has been changed to process them in the +order presented because it matches historical practice and is +more intuitive. +.LP +The treatment of the \fBp\fP flag to the \fBs\fP command differs between +System V and BSD-based systems when the default +output is suppressed. In the two examples: +.sp +.RS +.nf + +\fBecho a | sed 's/a/A/p' +echo a | sed -n 's/a/A/p' +\fP +.fi +.RE +.LP +this volume of IEEE\ Std\ 1003.1-2001, BSD, System V documentation, +and the SVID indicate that the first example should +write two lines with \fBA\fP, whereas the second should write one. +Some System V systems write the \fBA\fP only once in both +examples because the \fBp\fP flag is ignored if the \fB-n\fP option +is not specified. +.LP +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 +IEEE\ Std\ 1003.1-2001 because: +.IP " *" 3 +No known documentation for any historic system describes the interaction +between the \fBp\fP flag and the \fB-n\fP option. +.LP +.IP " *" 3 +The selected behavior is more correct as there is no technical justification +for any interaction between the \fBp\fP flag and +the \fB-n\fP option. A relationship between \fB-n\fP and the \fBp\fP +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 \fBD\fP, \fBd\fP, \fBq\fP, or +branching commands. Such scripts rely on the \fBp\fP suffix to write +the pattern space because they do not make use of the default +output at the "bottom" of the script. +.LP +.IP " *" 3 +Because the \fB-n\fP option makes the \fBp\fP flag unnecessary, any +interaction would only be useful if \fIsed\fP scripts +were written to run both with and without the \fB-n\fP option. This +is believed to be unlikely. It is even more unlikely that +programmers have coded the \fBp\fP 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. +.LP +.IP " *" 3 +Finally, scripts that break under the specified behavior produce too +much output instead of too little, which is easier to +diagnose and correct. +.LP +.LP +The form of the substitute command that uses the \fBn\fP 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 \fBs/a/A/2047\fP should be able to substitute the 2047th occurrence +of \fBa\fP on a line. +.LP +The \fBb\fP, \fBt\fP, and \fB:\fP commands are documented to ignore +leading white space, but no mention is made of trailing +white space. Historical implementations of \fIsed\fP assigned different +locations to the labels \fB'x'\fP and +\fB"x\ "\fP . 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 used +or jumps to labels that do not exist. +.LP +Historically, the \fIsed\fP \fB!\fP and \fB}\fP editing commands did +not permit multiple commands on a single line using a +semicolon as a command delimiter. Implementations are permitted, but +not required, to support this extension. +.SH FUTURE DIRECTIONS +.LP +None. +.SH SEE ALSO +.LP +\fIawk\fP, \fIed\fP, \fIgrep\fP +.SH COPYRIGHT +Portions of this text are reprinted and reproduced in electronic form +from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology +-- Portable Operating System Interface (POSIX), The Open Group Base +Specifications Issue 6, Copyright (C) 2001-2003 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 +http://www.opengroup.org/unix/online.html . |