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NAME bawk - text processor SYNOPSIS bawk rules [file] ... DESCRIPTION Bawk is a text processing program that searches files for specific patterns and performs "actions" for every occurrance of these patterns. The patterns can be "regular expressions" as used in the UNIX "ex" editor. The actions are expressed using a subset of the "C" language. The patterns and actions are usually placed in a "rules" file whose name must be the first argument in the command line. All other arguments are taken to be the names of text files on which the rules are to be applied. The special file name "-" may also be used anywhere on the command line to take input from the standard input device. The command: bawk - prog.c - prog.h would read the patterns and actions rules from the standard input, then apply them to the files "prog.c", the standard input and "prog.h" in that order. The general format of a rules file is: <pattern> { <action> } <pattern> { <action> } ... There may be any number of these <pattern> { <action> } sequences in the rules file. Bawk reads a line of input from the current input file and applies every <pattern> { <action> } in sequence to the line. If the <pattern> corresponding to any { <action> } is missing, the action is applied to every line of input. The default { <action> } is to print the matched input line. PATTERNS The <pattern>'s may consist of any valid C expression. If the <pattern> consists of two expressions seperated by a comma, it is taken to be a range and the <action> is performed on all lines of input that match the range. <pattern>'s may contain "regular expressions" delimited by an '@' symbol. Regular expressions can be thought of as a generalized "wildcard" string matching mechanism, similar to that used by many operating systems to specify file names. Regular expressions may contain any of the following characters: x An ordinary character (not mentioned below) matches that character. '\' The backslash quotes any character. "\$" matches a dollar-sign. '^' A circumflex at the beginning of an expression matches the beginning of a line. '$' A dollar-sign at the end of an expression matches the end of a line. '.' A period matches any single character except newline. ':x' A colon matches a class of characters described by the character following it: ':a' ":a" matches any alphabetic; ':d' ":d" matches digits; ':n' ":n" matches alphanumerics; ': ' ": " matches spaces, tabs, and other control characters, such as newline. '*' An expression followed by an asterisk matches zero or more occurrances of that expression: "fo*" matches "f", "fo", "foo", "fooo", etc. '+' An expression followed by a plus sign matches one or more occurrances of that expression: "fo+" matches "fo", "foo", "fooo", etc. '-' An expression followed by a minus sign optionally matches the expression. '[]' A string enclosed in square brackets matches any single character in that string, but no others. If the first character in the string is a circumflex, the expression matches any character except newline and the characters in the string. For example, "[xyz]" matches "xx" and "zyx", while "[^xyz]" matches "abc" but not "axb". A range of characters may be specified by two characters separated by "-". Note that, [a-z] matches alphabetics, while [z-a] never matches. For example, the following rules file would print every line that contained a valid C identifier: @[a-zA-Z][a-zA-Z0-9]@ And this rules file would print all lines between and including the ones that contained the word "START" and "END": @START@, @END@ ACTIONS Actions are expressed as a subset of the C language. All variables are global and default to int's if not formally declared. Variable declarations may appear anywhere within an action. Only char's and int's and pointers and arrays of char and int are allowed. Bawk allows only decimal integer constants to be used - no hex (0xnn) or octal (0nn). String and character constants may contain all of the special C escapes (\n, \r, etc.). Bawk supports the "if", "else", "while" and "break" flow of control constructs, which behave exactly as in C. Also supported are the following unary and binary operators, listed in order from highest to lowest precedence: operator type associativity () [] unary left to right ! ~ ++ -- - * & unary right to left * / % binary left to right + - binary left to right << >> binary left to right < <= > >= binary left to right == != binary left to right & binary left to right ^ binary left to right | binary left to right && binary left to right || binary left to right = binary right to left Comments are introduced by a '#' symbol and are terminated by the first newline character. The standard "/*" and "*/" comment delimiters are not supported and will result in a syntax error. FIELDS When bawk reads a line from the current input file, the record is automatically seperated into "fields". A field is simply a string of consecutive characters delimited by either the beginning or end of line, or a "field seperator" character Initially, the field seperators are the space and tab character. The special unary operator '$' is used to reference one of the fields in the current input record (line). The fields are numbered sequentially starting at 1. The expression "$0" references the entire input line. Similarly, the "record seperator" is used to determine the end of an input "line", initially the newline character. The field and record seperators may be changed programatically by one of the actions and will remain in effect until changed again. Fields behave exactly like strings; and can be used in the same context as a character array. These "arrays" can be considered to have been declared as: char ($n)[ 128 ]; In other words, they are 128 bytes long. Notice that the parentheses are necessary because the operators [] and $ associate from right to left; without them, the statement would have parsed as: char $(1[ 128 ]); which is obviously ridiculous. If the contents of one of these field arrays is altered, the "$0" field will reflect this change. For example, this expression: *$4 = 'A'; will change the first character of the fourth field to an upper-case letter 'A'. Then, when the following input line: 120 PRINT "Name address Zip" is processed, it would be printed as: 120 PRINT "Name Address Zip" Fields may also be modified with the strcpy() function (see below). For example, the expression: strcpy( $4, "Addr." ); applied to the same line above would yield: 120 PRINT "Name Addr. Zip" PREDEFINED VARIABLES The following variables are pre-defined: FS Field seperator (see below). RS Record seperator (see below also). NF Number of fields in current input record (line). NR Number of records processed thus far. FILENAME Name of current input file. BEGIN A special <pattern> that matches the beginning of input text, before the first record is read. END A special <pattern> that matches the end of input text, after the last record has been read. Bawk also provides some useful builtin functions for string manipulation and printing: printf(arg..) Exactly the printf() function from C. getline() Reads the next record from the current input file and returns 0 on end of file. nextfile() Closes out the current input file and begins processing the next file in the list (if any). strlen(s) Returns the length of its string argument. strcpy(s,t) Copies the string "t" to the string "s". strcmp(s,t) Compares the "s" to "t" and returns 0 if they match. toupper(c) Returns its character argument converted to upper-case. tolower(c) Returns its character argument converted to lower-case. match(s,@re@) Compares the string "s" to the regular expression "re" and returns the number of matches found (zero if none). EXAMPLES The following rules file will scan a C program, counting the number of mismatched parentheses, brackets, and braces. /[()\[\]{}]/ { parens = parens + match( $0, @(@ ); parens = parens - match( $0, @)@ ); bracks = bracks + match( $0, @[@ ); bracks = bracks - match( $0, @]@ ); braces = braces + match( $0, @{@ ); braces = braces - match( $0, @}@ ); } END { printf("parens=%d, brackets=%d, braces=%d\n", parens, bracks, braces ); } This program will capitalize the first word in every sentence of a document: BEGIN { RS = '.'; # set record seperator to a period } { if ( match( $1, @^[a-z]@ ) ) *$1 = toupper( *$1 ); printf( "%s\n", $0 ); } LIMITATIONS Bawk was originally written in BDS C, but every attempt was made to keep the code as portable as possible. The program should be compilable with any "standard" C compiler. On CP/M systems compiled with BDS C, bawk takes up about 24K. An input record may be no longer than 128 characters. If longer records are encountered, they terminate prematurely and the next record starts where the previous one was hacked off. A single pattern or action statement may be no longer than about 4K characters, excluding comments and whitespace. Since the program is semi-compiled the tokenized version will probably wind up being smaller than the source code, so the 4K figure is only approximate. AUTHOR Bob Brodt 486 Linden Ave. Bogota, NJ 07603 ACKNOWLEDGEMENTS The concept for bawk (and 3/4 of the name!) was taken from the program "awk" written by Afred V. Aho, Brian W. Kernighan and Peter J. Weinberger. My apologies for any irreverences. The regular expression compiler/parser was borrowed from a program called "grep" and has been highly modified. Grep is distributed by the DEC Users Society (DECUS) and is Copyright (C) 1980 by DECUS. The author acknowledges DECUS with a nod of thanks for giving their general permission and okey-dokey to copy or modify the grep program. UNIX is a trademark of AT&T Bell Labs.