GAWK: Effective AWK Programming

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48 GAWK: Effective AWK Programmingprint $1The output is ‘aCa’. If you really want to split fields on an alphabetic character while ignoringcase, use a regexp that will do it for you. E.g., ‘FS = "[c]"’. In this case, IGNORECASEwill take effect.3.6 Reading Fixed-Width DataNOTE: This section discusses an advanced feature of gawk. If you are a noviceawk user, you might want to skip it on the first reading.gawk version 2.13 introduced a facility for dealing with fixed-width fields with no distinctivefield separator. For example, data of this nature arises in the input for old Fortranprograms where numbers are run together, or in the output of programs that did not anticipatethe use of their output as input for other programs.An example of the latter is a table where all the columns are lined up by the use ofa variable number of spaces and empty fields are just spaces. Clearly, awk’s normal fieldsplitting based on FS does not work well in this case. Although a portable awk programcan use a series of substr calls on $0 (see Section 8.1.3 [String-Manipulation Functions],page 132), this is awkward and inefficient for a large number of fields.The splitting of an input record into fixed-width fields is specified by assigning a stringcontaining space-separated numbers to the built-in variable FIELDWIDTHS. Each numberspecifies the width of the field, including columns between fields. If you want to ignore thecolumns between fields, you can specify the width as a separate field that is subsequentlyignored. It is a fatal error to supply a field width that is not a positive number. The followingdata is the output of the Unix w utility. It is useful to illustrate the use of FIELDWIDTHS:10:06pm up 21 days, 14:04, 23 usersUser tty login idle JCPU PCPU whathzuo ttyV0 8:58pm 9 5 vi p24.texhzang ttyV3 6:37pm 50 -csheklye ttyV5 9:53pm 7 1 em thes.texdportein ttyV6 8:17pm 1:47 -cshgierd ttyD3 10:00pm 1 elmdave ttyD4 9:47pm 4 4 wbrent ttyp0 26Jun91 4:46 26:46 4:41 bashdave ttyq4 26Jun9115days 46 46 wnewmailThe following program takes the above input, converts the idle time to number of seconds,and prints out the first two fields and the calculated idle time:NOTE: This program uses a number of awk features that haven’t been introducedyet.BEGIN { FIELDWIDTHS = "9 6 10 6 7 7 35" }NR > 2 {idle = $4sub(/^ */, "", idle) # strip leading spacesif (idle == "")idle = 0if (idle ~ /:/) {
Chapter 3: Reading Input Files 49}split(idle, t, ":")idle = t[1] * 60 + t[2]}if (idle ~ /days/)idle *= 24 * 60 * 60print $1, $2, idleRunning the program on the data produces the following results:hzuo ttyV0 0hzang ttyV3 50eklye ttyV5 0dportein ttyV6 107gierd ttyD3 1dave ttyD4 0brent ttyp0 286dave ttyq4 1296000Another (possibly more practical) example of fixed-width input data is the input froma deck of balloting cards. In some parts of the United States, voters mark their choices bypunching holes in computer cards. These cards are then processed to count the votes forany particular candidate or on any particular issue. Because a voter may choose not to voteon some issue, any column on the card may be empty. An awk program for processing suchdata could use the FIELDWIDTHS feature to simplify reading the data. (Of course, gettinggawk to run on a system with card readers is another story!)Assigning a value to FS causes gawk to use FS for field splitting again. Use ‘FS = FS’ tomake this happen, without having to know the current value of FS. In order to tell whichkind of field splitting is in effect, use PROCINFO["FS"] (see Section 6.5.2 [Built-in VariablesThat Convey Information], page 113). The value is "FS" if regular field splitting is beingused, or it is "FIELDWIDTHS" if fixed-width field splitting is being used:if (PROCINFO["FS"] == "FS")regular field splitting ...elsefixed-width field splitting ...This information is useful when writing a function that needs to temporarily change FSor FIELDWIDTHS, read some records, and then restore the original settings (see Section 12.5[Reading the User Database], page 206, for an example of such a function).3.7 Multiple-Line RecordsIn some databases, a single line cannot conveniently hold all the information in one entry.In such cases, you can use multiline records. The first step in doing this is to choose yourdata format.One technique is to use an unusual character or string to separate records. For example,you could use the formfeed character (written ‘\f’ in awk, as in C) to separate them, makingeach record a page of the file. To do this, just set the variable RS to "\f" (a string containing
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GAWK: Effective AWK Programming

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