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edpatterson

10-28-2010 04:28 PM

Loops in Bash shell or variable math...

I am trying to map the coordinates of a grid.

Code:

R=7    # number of rows (lines)

C=6    # number of columns

X=200  # initial horizontal location

Y=100  # initial vertical location

XDIS=25 # horizontal distance cell to cell

YDIS=26 # vertical distance cell to cell

XORG=$X # used to begin each row

for i in $(eval echo {1..$R}; do  # works, based upon other help

  for j in $(eval echo {1..$C}; do # works, based upon other help

    echo "$Y:$X"

    $X=$X+$XDIS # This is what is blowing up

  done

  $X=$XORG      # I am assuming this will not work either

  $Y=$Y+YDIS    # ""

done

impert

10-28-2010 04:41 PM

Quote:

$X=$X+$XDIS # This is what is blowing up

Try:
X=$(($X+$XDIS))
1 The assignment should not start with the $
2 Arithmetic is done within $(( ))

Quote:

$X=$XORG # I am assuming this will not work either
$Y=$Y+YDIS # ""

I'd say those are fair assumptions.

I'm only learning myself, so if I've led you astray, my apologies.
It's a good idea to try snippets of code in a terminal.

edpatterson

10-28-2010 04:55 PM

Thanks! That did it.

Thanks!

Ed

GrapefruiTgirl

10-28-2010 05:01 PM

Also, for the sake of completeness, you don't need the $ inside the $(()) like below:

Code:

X=$((a+b)

That will work just as well. :)

grail

10-29-2010 01:09 AM

Or maybe even:

Code:

for ((i=1; i <= $R; i++))

  for ((j=1; j <= $C; j++))

    echo "$Y:$X"

    ((X+=XDIS))

  done



  ((X=XORG))  # changed this one only to keep all numeric changes the same

  ((Y+=YDIS))

done

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