GAWK: Effective AWK Programming

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134 GAWK: Effective AWK Programming$ nawk ’BEGIN { print length(x) ; x[1] = 1 }’⊣ 0If ‘--lint’ has been specified on the command line, gawk issues a warning aboutthis.Beginning with gawk version 3.1.5, when supplied an array argument, thelength function returns the number of elements in the array. This is less usefulthan it might seem at first, as the array is not guaranteed to be indexed fromone to the number of elements in it. If ‘--lint’ is provided on the commandline (see Section 11.2 [Command-Line Options], page 177), gawk warns thatpassing an array argument is not portable. If ‘--posix’ is supplied, using anarray argument is a fatal error (see Chapter 7 [Arrays in awk], page 119).match(string, regexp [, array])The match function searches string for the longest, leftmost substring matchedby the regular expression, regexp. It returns the character position, or index,at which that substring begins (one, if it starts at the beginning of string). Ifno match is found, it returns zero.The regexp argument may be either a regexp constant (‘/.../’) or a stringconstant (". . ."). In the latter case, the string is treated as a regexp to bematched. Section 2.8 [Using Dynamic Regexps], page 34, for a discussion of thedifference between the two forms, and the implications for writing your programcorrectly.The order of the first two arguments is backwards from most other string functionsthat work with regular expressions, such as sub and gsub. It might help toremember that for match, the order is the same as for the ‘~’ operator: ‘string~ regexp’.The match function sets the built-in variable RSTART to the index. It alsosets the built-in variable RLENGTH to the length in characters of the matchedsubstring. If no match is found, RSTART is set to zero, and RLENGTH to −1.For example:{if ($1 == "FIND")regex = $2else {where = match($0, regex)if (where != 0)print "Match of", regex, "found at",where, "in", $0}}This program looks for lines that match the regular expression stored in thevariable regex. This regular expression can be changed. If the first word on aline is ‘FIND’, regex is changed to be the second word on that line. Therefore,if given:FIND ru+nMy program runs
Chapter 8: Functions 135awk prints:but not very quicklyFIND MelvinJF+KMThis line is property of Reality Engineering Co.Melvin was here.Match of ru+n found at 12 in My program runsMatch of Melvin found at 1 in Melvin was here.If array is present, it is cleared, and then the 0th element of array is set tothe entire portion of string matched by regexp. If regexp contains parentheses,the integer-indexed elements of array are set to contain the portion of stringmatching the corresponding parenthesized subexpression. For example:$ echo foooobazbarrrrr |> gawk ’{ match($0, /(fo+).+(bar*)/, arr)> print arr[1], arr[2] }’⊣ foooo barrrrrIn addition, beginning with gawk 3.1.2, multidimensional subscripts are availableproviding the start index and length of each matched subexpression:$ echo foooobazbarrrrr |> gawk ’{ match($0, /(fo+).+(bar*)/, arr)> print arr[1], arr[2]> print arr[1, "start"], arr[1, "length"]> print arr[2, "start"], arr[2, "length"]> }’⊣ foooo barrrrr⊣ 1 5⊣ 9 7There may not be subscripts for the start and index for every parenthesizedsubexpressions, since they may not all have matched text; thus they should betested for with the in operator (see Section 7.2 [Referring to an Array Element],page 120).The array argument to match is a gawk extension. In compatibility mode (seeSection 11.2 [Command-Line Options], page 177), using a third argument is afatal error.split(string, array [, fieldsep])This function divides string into pieces separated by fieldsep and stores thepieces in array. The first piece is stored in array[1], the second piece inarray[2], and so forth. The string value of the third argument, fieldsep, is aregexp describing where to split string (much as FS can be a regexp describingwhere to split input records). If fieldsep is omitted, the value of FS is used.split returns the number of elements created.The split function splits strings into pieces in a manner similar to the wayinput lines are split into fields. For example:split("cul-de-sac", a, "-")
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