The Datafile PD-CD 4

home *** CD-ROM | disk | FTP | other *** search

/ The Datafile PD-CD 4 / DATAFILE_PDCD4.iso / unix / riscbsd / datafile / usd / 18_sed / sed_txt

Wrap

Text File | 1996-10-12 | 28.0 KB | 859 lines

SED -- A Non-interactive Text Editor Lee E. McMahon ABSTRACT Sed is a non-interactive context editor that runs on the UNIX(R) operating system. Sed is designed to be especially useful in three cases: 1) To edit files too large for comfortable interactive editing; 2) To edit any size file when the sequence of editing commands is too complicated to be comfortably typed in interactive mode. 3) To perform multiple `global' editing functions effi- ciently in one pass through the input. This memorandum constitutes a manual for users of sed. Introduction Sed is a non-interactive context editor designed to be espe- cially useful in three cases: 1) To edit files too large for comfortable interactive edit- ing; 2) To edit any size file when the sequence of editing com- mands is too complicated to be comfortably typed in interac- tive mode; 3) To perform multiple `global' editing functions effi- ciently in one pass through the input. Since only a few lines of the input reside in core at one time, and no temporary files are used, the effective size of file that can be edited is limited only by the requirement that the input and output fit simultaneously into available secondary storage. Complicated editing scripts can be created separately and given to sed as a command file. For complex edits, this saves considerable typing, and its attendant errors. Sed running from a command file is much more efficient than any interactive editor known to the author, even if that editor can be driven by a pre-written script. USD:18-2 SED -- A Non-interactive Text Editor The principal loss of functions compared to an interactive editor are lack of relative addressing (because of the line- at-a-time operation), and lack of immediate verification that a command has done what was intended. Sed is a lineal descendant of the UNIX editor, ed. Because of the differences between interactive and non-interactive operation, considerable changes have been made between ed and sed; even confirmed users of ed will frequently be sur- prised (and probably chagrined), if they rashly use sed without reading Sections 2 and 3 of this document. The most striking family resemblance between the two editors is in the class of patterns (`regular expressions') they recog- nize; the code for matching patterns is copied almost verba- tim from the code for ed, and the description of regular expressions in Section 2 is copied almost verbatim from the UNIX Programmer's Manual[1]. (Both code and description were written by Dennis M. Ritchie.) 1. Overall Operation Sed by default copies the standard input to the standard output, perhaps performing one or more editing commands on each line before writing it to the output. This behavior may be modified by flags on the command line; see Section 1.1 below. The general format of an editing command is: [address1,address2][function][arguments] One or both addresses may be omitted; the format of addresses is given in Section 2. Any number of blanks or tabs may separate the addresses from the function. The function must be present; the available commands are dis- cussed in Section 3. The arguments may be required or optional, according to which function is given; again, they are discussed in Section 3 under each individual function. Tab characters and spaces at the beginning of lines are ignored. 1.1. Command-line Flags Three flags are recognized on the command line: -n: tells sed not to copy all lines, but only those specified by p functions or p flags after s func- tions (see Section 3.3); -e: tells sed to take the next argument as an editing command; -f: tells sed to take the next argument as a file name; the file should contain editing commands, one to a SED -- A Non-interactive Text Editor USD:18-3 line. 1.2. Order of Application of Editing Commands Before any editing is done (in fact, before any input file is even opened), all the editing commands are compiled into a form which will be moderately efficient during the execu- tion phase (when the commands are actually applied to lines of the input file). The commands are compiled in the order in which they are encountered; this is generally the order in which they will be attempted at execution time. The com- mands are applied one at a time; the input to each command is the output of all preceding commands. The default linear order of application of editing commands can be changed by the flow-of-control commands, t and b (see Section 3). Even when the order of application is changed by these commands, it is still true that the input line to any command is the output of any previously applied command. 1.3. Pattern-space The range of pattern matches is called the pattern space. Ordinarily, the pattern space is one line of the input text, but more than one line can be read into the pattern space by using the N command (Section 3.6.). 1.4. Examples Examples are scattered throughout the text. Except where otherwise noted, the examples all assume the following input text: In Xanadu did Kubla Khan A stately pleasure dome decree: Where Alph, the sacred river, ran Through caverns measureless to man Down to a sunless sea. (In no case is the output of the sed commands to be consid- ered an improvement on Coleridge.) Example: The command 2q will quit after copying the first two lines of the input. The output will be: USD:18-4 SED -- A Non-interactive Text Editor In Xanadu did Kubla Khan A stately pleasure dome decree: 2. ADDRESSES: Selecting lines for editing Lines in the input file(s) to which editing commands are to be applied can be selected by addresses. Addresses may be either line numbers or context addresses. The application of a group of commands can be controlled by one address (or address-pair) by grouping the commands with curly braces (`{ }')(Sec. 3.6.). 2.1. Line-number Addresses A line number is a decimal integer. As each line is read from the input, a line-number counter is incremented; a line-number address matches (selects) the input line which causes the internal counter to equal the address line- number. The counter runs cumulatively through multiple input files; it is not reset when a new input file is opened. As a special case, the character $ matches the last line of the last input file. 2.2. Context Addresses A context address is a pattern (`regular expression') enclosed in slashes (`/'). The regular expressions recog- nized by sed are constructed as follows: 1) An ordinary character (not one of those discussed below) is a regular expression, and matches that character. 2) A circumflex `^' at the beginning of a regular expression matches the null character at the beginning of a line. 3) A dollar-sign `$' at the end of a regular expression matches the null character at the end of a line. 4) The characters `\n' match an imbedded newline character, but not the newline at the end of the pattern space. 5) A period `.' matches any character except the terminal newline of the pattern space. 6) A regular expression followed by an asterisk `*' matches any number (including 0) of adjacent occurrences of the reg- ular expression it follows. 7) A string of characters in square brackets `[ ]' matches any character in the string, and no others. If, however, the first character of the string is circumflex `^', the regular expression matches any character except the charac- ters in the string and the terminal newline of the pattern space. 8) A concatenation of regular expressions is a regular SED -- A Non-interactive Text Editor USD:18-5 expression which matches the concatenation of strings matched by the components of the regular expression. 9) A regular expression between the sequences `$' and `$' is identical in effect to the unadorned regular expression, but has side-effects which are described under the s command below and specification 10) immediately below. 10) The expression `\d' means the same string of characters matched by an expression enclosed in `$' and `$' earlier in the same pattern. Here d is a single digit; the string specified is that beginning with the dth occurrence of `$' counting from the left. For example, the expression `^\(.*$\1' matches a line beginning with two repeated occurrences of the same string. 11) The null regular expression standing alone (e.g., `//') is equivalent to the last regular expression compiled. To use one of the special characters (^ $ . * [ ] \ /) as a literal (to match an occurrence of itself in the input), precede the special character by a backslash `\'. For a context address to `match' the input requires that the whole pattern within the address match some portion of the pattern space. 2.3. Number of Addresses The commands in the next section can have 0, 1, or 2 addresses. Under each command the maximum number of allowed addresses is given. For a command to have more addresses than the maximum allowed is considered an error. If a command has no addresses, it is applied to every line in the input. If a command has one address, it is applied to all lines which match that address. If a command has two addresses, it is applied to the first line which matches the first address, and to all subsequent lines until (and including) the first subsequent line which matches the second address. Then an attempt is made on sub- sequent lines to again match the first address, and the pro- cess is repeated. Two addresses are separated by a comma. Examples: /an/ matches lines 1, 3, 4 in our sample text /an.*an/ matches line 1 /^an/ matches no lines /./ matches all lines /\./ matches line 5 /r*an/ matches lines 1,3, 4 (number = zero!) USD:18-6 SED -- A Non-interactive Text Editor /$an$.*\1/ matches line 1 3. FUNCTIONS All functions are named by a single character. In the fol- lowing summary, the maximum number of allowable addresses is given enclosed in parentheses, then the single character function name, possible arguments enclosed in angles (< >), an expanded English translation of the single-character name, and finally a description of what each function does. The angles around the arguments are not part of the argu- ment, and should not be typed in actual editing commands. 3.1. Whole-line Oriented Functions (2)d -- delete lines The d function deletes from the file (does not write to the output) all those lines matched by its address(es). It also has the side effect that no further commands are attempted on the corpse of a deleted line; as soon as the d function is executed, a new line is read from the input, and the list of editing commands is re- started from the beginning on the new line. (2)n -- next line The n function reads the next line from the input, replacing the current line. The current line is written to the output if it should be. The list of editing commands is continued following the n command. (1)a\ <text> -- append lines The a function causes the argument <text> to be written to the output after the line matched by its address. The a command is inherently multi- line; a must appear at the end of a line, and <text> may contain any number of lines. To pre- serve the one-command-to-a-line fiction, the inte- rior newlines must be hidden by a backslash char- acter (`\') immediately preceding the newline. The <text> argument is terminated by the first unhidden newline (the first one not immediately preceded by backslash). Once an a function is successfully executed, <text> will be written to the output regardless of what later commands do to the line which triggered it. The triggering line may be deleted entirely; <text> will still be written to the output. The <text> is not scanned for address matches, and no editing commands are attempted on it. It does not cause any change in the line-number counter. (1)i\ <text> -- insert lines The i function behaves identically to the a func- tion, except that <text> is written to the output SED -- A Non-interactive Text Editor USD:18-7 before the matched line. All other comments about the a function apply to the i function as well. (2)c\ <text> -- change lines The c function deletes the lines selected by its address(es), and replaces them with the lines in <text>. Like a and i, c must be followed by a newline hidden by a backslash; and interior new lines in <text> must be hidden by backslashes. The c command may have two addresses, and there- fore select a range of lines. If it does, all the lines in the range are deleted, but only one copy of <text> is written to the output, not one copy per line deleted. As with a and i, <text> is not scanned for address matches, and no editing com- mands are attempted on it. It does not change the line-number counter. After a line has been deleted by a c function, no further commands are attempted on the corpse. If text is appended after a line by a or r functions, and the line is subsequently changed, the text inserted by the c function will be placed before the text of the a or r functions. (The r function is described in Section 3.4.) Note: Within the text put in the output by these functions, leading blanks and tabs will disappear, as always in sed commands. To get leading blanks and tabs into the output, precede the first desired blank or tab by a backslash; the backslash will not appear in the output. Example: The list of editing commands: n a\ XXXX d applied to our standard input, produces: In Xanadu did Kubhla Khan XXXX Where Alph, the sacred river, ran XXXX Down to a sunless sea. In this particular case, the same effect would be produced by either of the two following command lists: n n i\ c\ XXXX XXXX d USD:18-8 SED -- A Non-interactive Text Editor 3.2. Substitute Function One very important function changes parts of lines selected by a context search within the line. (2)s<pattern><replacement><flags> -- substitute The s function replaces part of a line (selected by <pattern>) with <replacement>. It can best be read: Substitute for <pattern>, <replacement> The <pattern> argument contains a pattern, exactly like the patterns in addresses (see 2.2 above). The only difference between <pattern> and a con- text address is that the context address must be delimited by slash (`/') characters; <pattern> may be delimited by any character other than space or newline. By default, only the first string matched by <pattern> is replaced, but see the g flag below. The <replacement> argument begins immediately after the second delimiting character of <pattern>, and must be followed immediately by another instance of the delimiting character. (Thus there are exactly three instances of the de- limiting character.) The <replacement> is not a pattern, and the characters which are special in patterns do not have special meaning in <replace- ment>. Instead, other characters are special: & is replaced by the string matched by <pattern> \d (where d is a single digit) is replaced by the dth substring matched by parts of <pattern> enclosed in `$' and `$'. If nested substrings occur in <pattern>, the dth is determined by counting open- ing delimiters (`\('). As in patterns, special characters may be made literal by preceding them with backslash (`\'). The <flags> argument may contain the following flags: g -- substitute <replacement> for all (non- overlapping) instances of <pattern> in the line. After a successful substitu- tion, the scan for the next instance of <pattern> begins just after the end of the inserted characters; characters put into the line from <replacement> are not rescanned. p -- print the line if a successful replace- ment was done. The p flag causes the line to be written to the output if and only if a substitution was actually made by the s function. Notice that if sev- eral s functions, each followed by a p flag, successfully substitute in the same input line, multiple copies of the SED -- A Non-interactive Text Editor USD:18-9 line will be written to the output: one for each successful substitution. w <filename> -- write the line to a file if a successful replacement was done. The w flag causes lines which are actually substituted by the s function to be written to a file named by <filename>. If <filename> exists before sed is run, it is overwritten; if not, it is cre- ated. A single space must separate w and <filename>. The possibilities of multiple, somewhat different copies of one input line being written are the same as for p. A maximum of 10 differ- ent file names may be mentioned after w flags and w functions (see below), com- bined. Examples: The following command, applied to our standard input, s/to/by/w changes produces, on the standard output: In Xanadu did Kubhla Khan A stately pleasure dome decree: Where Alph, the sacred river, ran Through caverns measureless by man Down by a sunless sea. and, on the file `changes': Through caverns measureless by man Down by a sunless sea. If the nocopy option is in effect, the command: s/[.,;?:]/*P&*/gp produces: A stately pleasure dome decree*P:* Where Alph*P,* the sacred river*P,* ran Down to a sunless sea*P.* Finally, to illustrate the effect of the g flag, the com- mand: /X/s/an/AN/p produces (assuming nocopy mode): USD:18-10 SED -- A Non-interactive Text Editor In XANadu did Kubhla Khan and the command: /X/s/an/AN/gp produces: In XANadu did Kubhla KhAN 3.3. Input-output Functions (2)p -- print The print function writes the addressed lines to the standard output file. They are writ- ten at the time the p function is encountered, regardless of what succeeding editing commands may do to the lines. (2)w <filename> -- write on <filename> The write func- tion writes the addressed lines to the file named by <filename>. If the file previously existed, it is overwritten; if not, it is created. The lines are written exactly as they exist when the write function is encountered for each line, regardless of what subsequent editing commands may do to them. Exactly one space must separate the w and <filename>. A maximum of ten different files may be mentioned in write functions and w flags after s functions, combined. (1)r <filename> -- read the contents of a file The read function reads the contents of <filename>, and appends them after the line matched by the address. The file is read and appended regardless of what subsequent editing commands do to the line which matched its address. If r and a functions are executed on the same line, the text from the a functions and the r functions is written to the output in the order that the functions are exe- cuted. Exactly one space must separate the r and <filename>. If a file mentioned by a r function cannot be opened, it is considered a null file, not an error, and no diagnostic is given. NOTE: Since there is a limit to the number of files that can be opened simultaneously, care should be taken that no more than ten files be mentioned in w functions or flags; that number is reduced by one if any r functions are present. (Only one read file is open at one time.) Examples Assume that the file `note1' has the following contents: Note: Kubla Khan (more properly Kublai Khan; 1216-1294) was the grandson and most eminent SED -- A Non-interactive Text Editor USD:18-11 successor of Genghiz (Chingiz) Khan, and founder of the Mongol dynasty in China. Then the following command: /Kubla/r note1 produces: In Xanadu did Kubla Khan Note: Kubla Khan (more properly Kublai Khan; 1216-1294) was the grandson and most eminent suc- cessor of Genghiz (Chingiz) Khan, and founder of the Mongol dynasty in China. A stately pleasure dome decree: Where Alph, the sacred river, ran Through caverns measureless to man Down to a sunless sea. 3.4. Multiple Input-line Functions Three functions, all spelled with capital letters, deal spe- cially with pattern spaces containing imbedded newlines; they are intended principally to provide pattern matches across lines in the input. (2)N -- Next line The next input line is appended to the current line in the pattern space; the two input lines are separated by an imbedded newline. Pattern matches may extend across the imbedded newline(s). (2)D -- Delete first part of the pattern space Delete up to and including the first newline character in the current pattern space. If the pattern space becomes empty (the only newline was the terminal newline), read another line from the input. In any case, begin the list of editing commands again from its beginning. (2)P -- Print first part of the pattern space Print up to and including the first newline in the pattern space. The P and D functions are equivalent to their lower-case counterparts if there are no imbedded newlines in the pat- tern space. 3.5. Hold and Get Functions Four functions save and retrieve part of the input for pos- sible later use. (2)h -- hold pattern space The h functions copies the contents of the pattern space into a hold area (destroying the previous contents of the hold area). (2)H -- Hold pattern space The H function appends the USD:18-12 SED -- A Non-interactive Text Editor contents of the pattern space to the contents of the hold area; the former and new contents are separated by a newline. (2)g -- get contents of hold area The g function copies the contents of the hold area into the pattern space (destroying the previous contents of the pattern space). (2)G -- Get contents of hold area The G function appends the contents of the hold area to the con- tents of the pattern space; the former and new contents are separated by a newline. (2)x -- exchange The exchange command interchanges the contents of the pattern space and the hold area. Example The commands 1h 1s/ did.*// 1x G s/\n/ :/ applied to our standard example, produce: In Xanadu did Kubla Khan :In Xanadu A stately pleasure dome decree: :In Xanadu Where Alph, the sacred river, ran :In Xanadu Through caverns measureless to man :In Xanadu Down to a sunless sea. :In Xanadu 3.6. Flow-of-Control Functions These functions do no editing on the input lines, but con- trol the application of functions to the lines selected by the address part. (2)! -- Don't The Don't command causes the next command (written on the same line), to be applied to all and only those input lines not selected by the adress part. (2){ -- Grouping The grouping command `{' causes the next set of commands to be applied (or not applied) as a block to the input lines selected by the addresses of the grouping command. The first of the commands under control of the grouping may appear on the same line as the `{' or on the next line. The group of commands is terminated by a matching `}' stand- ing on a line by itself. Groups can be nested. (0):<label> -- place a label The label function marks a place in the list of editing commands which may be referred to by b and t functions. The <label> may be any sequence of eight or fewer characters; if two different colon functions SED -- A Non-interactive Text Editor USD:18-13 have identical labels, a compile time diagnostic will be generated, and no execution attempted. (2)b<label> -- branch to label The branch function causes the sequence of editing commands being applied to the cur- rent input line to be restarted immediately after the place where a colon function with the same <label> was encoun- tered. If no colon function with the same label can be found after all the editing commands have been compiled, a compile time diagnostic is produced, and no execution is attempted. A b function with no <label> is taken to be a branch to the end of the list of editing commands; whatever should be done with the current input line is done, and another input line is read; the list of editing commands is restarted from the beginning on the new line. (2)t<label> -- test substitutions The t function tests whether any successful substitutions have been made on the current input line; if so, it branches to <label>; if not, it does nothing. The flag which indicates that a successful substitution has been executed is reset by: 1) reading a new input line, or 2) executing a t function. 3.7. Miscellaneous Functions (1)= -- equals The = function writes to the standard output the line number of the line matched by its address. (1)q -- quit The q function causes the current line to be written to the output (if it should be), any appended or read text to be written, and execution to be terminated. Reference [1] Ken Thompson and Dennis M. Ritchie, The UNIX Program- mer's Manual. Bell Laboratories, 1978.