-----------------------------------------------------------------------------
Awk -- using arguments without reading them as files
  Read in the arguments using the ARGV variable but then you have to null
out the elements of the ARGV array as you snarf them up.  Otherwise nawk
will try to open them as files when the main scanning loop begins.

#!/bin/nawk -f
   BEGIN { awkoption = ARGV[1]; delete ARGV[1] }
   ...

NOTE: if delete ARGV[1] fails try ARGV[1]="" or "/dev/null"
                                       --- Ken Manheimer --- klm@cme.nist.gov

-----------------------------------------------------------------------------
awk two files but different actions
   This could be used to read a config or a table of data before the data
to awk.
   Variable settings take effect when they are encountered on the command
line, so, for example, you could instruct awk on how to behave for
different files using this technique.  For example:

  awk '{ program that depends on s }' s=1 file1 s=0 file2

Note that some versions of awk will cause variable settings encountered
before any real filenames to take effect before the BEGIN block is
executed, but some won't so neither way should be relied upon.

-----------------------------------------------------------------------------
Arrays are possible in awk
        # found that bitmap[$0] would not work.
        # so assign to variables.
        coordx = $1
        coordy = $2
        # assign "X" to that element of array 
        bitmap[coordx,coordy] = "X"

-----------------------------------------------------------------------------
Reading from commands in awk
The trick is to CLOSE the file that you use for the command pipe

    "date" | getline x;   close "date";

-----------------------------------------------------------------------------
Getting a return interger

  awk 'END{ exit 7 }'
  value=$?
  echo value

-----------------------------------------------------------------------------
Multiple Value returns from awk...

To do this have awk output a shell script. You can then have awk define as
many variables as you like.

eval `awk '
   END { print "FLAG="(NR > 0) ? 1 : 0 }
' -`

if [ "$FLAG" = 1 ] ; then
    echo "FLAG=$FLAG"
fi

-----------------------------------------------------------------------------
Changing the record seperator inside an awk script.

Awk reads and record separates its input before the script properly starts
as such you need to get it to re-evaluate that input.

For example...
    awk 'BEGIN { RS=";" }
         { $1=$1; printf "%s%1s\n",$0,";" }
        ' infile

The $1=$1 is required to get awk to re-compute the $0 for the first record.


-----------------------------------------------------------------------------
Determine which column numbers of relevant 'ps' fields

CMDCOL=`ps -e | awk '
        NR == 1 {
                for (i = 1; i <= NF; i++)
                        if      ($i == "COMMAND" || $i == "CMD" || $i == "COMD")
                                cmdcol = i
                }
        END     {
                print cmdcol
                }
'`

if [ "$CMDCOL" = "" ]
then
        echo "$0: Unrecognised ps format for COMMAND field"
        exit 1
fi

TTYCOL=`ps -e | awk '
        NR == 1 {
                for (i = 1; i <= NF; i++)
                        if      ($i == "TTY")
                                ttycol = i
                }
        END     {
                print ttycol
                }
'`

if [ "$TTYCOL" = "" ]
then
        echo "$0: Unrecognised ps format for TTY field"
        exit 1
fi

#
# Print list of all terminals running program
#
TTYLIST=`ps -e | awk ' $'"$CMDCOL"' == "vi" { print $'"$TTYCOL"' }'`

echo Terminals running vi:
echo $TTYLIST

-----------------------------------------------------------------------------