Reading Fixed-width Data
========================

   (This section discusses an advanced, experimental feature.  If you
are a novice `awk' user, you may wish to skip it on the first reading.)

   `gawk' 2.13 introduced a new facility for dealing with fixed-width
fields with no distinctive field separator.  Data of this nature arises
typically in one of at least two ways:  the input for old FORTRAN
programs where numbers are run together, and the output of programs
that did not anticipate the 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 of a variable number of spaces and *empty fields are just
spaces*.  Clearly, `awk''s normal field splitting based on `FS' will
not work well in this case.  (Although a portable `awk' program can use
a series of `substr' calls on `$0', 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 string containing space-separated numbers to
the built-in variable `FIELDWIDTHS'.  Each number specifies the width
of the field *including* columns between fields.  If you want to ignore
the columns between fields, you can specify the width as a separate
field that is subsequently ignored.

   The following data is the output of the `w' utility.  It is useful
to illustrate the use of `FIELDWIDTHS'.

      10:06pm  up 21 days, 14:04,  23 users
     User     tty       login  idle   JCPU   PCPU  what
     hzuo     ttyV0     8:58pm            9      5  vi p24.tex
     hzang    ttyV3     6:37pm    50                -csh
     eklye    ttyV5     9:53pm            7      1  em thes.tex
     dportein ttyV6     8:17pm  1:47                -csh
     gierd    ttyD3    10:00pm     1                elm
     dave     ttyD4     9:47pm            4      4  w
     brent    ttyp0    26Jun91  4:46  26:46   4:41  bash
     dave     ttyq4    26Jun9115days     46     46  wnewmail

   The 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.  (This program uses a number of `awk' features
that haven't been introduced yet.)

     BEGIN  { FIELDWIDTHS = "9 6 10 6 7 7 35" }
     NR > 2 {
         idle = $4
         sub(/^  */, "", idle)   # strip leading spaces
         if (idle == "") idle = 0
         if (idle ~ /:/) { split(idle, t, ":"); idle = t[1] * 60 + t[2] }
         if (idle ~ /days/) { idle *= 24 * 60 * 60 }
     
         print $1, $2, idle
     }

   Here is the result of running the program on the data:

     hzuo      ttyV0  0
     hzang     ttyV3  50
     eklye     ttyV5  0
     dportein  ttyV6  107
     gierd     ttyD3  1
     dave      ttyD4  0
     brent     ttyp0  286
     dave      ttyq4  1296000

   Another (possibly more practical) example of fixed-width input data
would be the input from a deck of balloting cards.  In some parts of
the United States, voters make their choices by punching holes in
computer cards.  These cards are then processed to count the votes for
any particular candidate or on any particular issue.  Since a voter may
choose not to vote on some issue, any column on the card may be empty.
An `awk' program for processing such data could use the `FIELDWIDTHS'
feature to simplify reading the data.

   This feature is still experimental, and will likely evolve over time.