I would like to run a for loop for a set of variables which I incorrectly denote as {A,B}. Following that my script looks like:
#!/bin/sh
for {A,B} in {1,2} {3,4} {5,6} {7,8}
do
echo A=$A B=$B
C=$(($A+$B))
echo Sum,C = $C
done
How can I correct it?
I would use
while read A B
do echo A=$A B=$B
C=$(( $A + $B ))
echo Sum,C = $C
done<<EOF
1 2
3 4
5 6
7 8
EOF
For more complex operations dc is your friend (polish reverse notation!)
C=$(echo "$A $B +pq"|dc)
set 1 2 3 4 5 6 7 8
while [ "$#" -gt 0 ]
do C="$(($1+$2))"
shift 2
done
for doesn't allow for two simultaneous assignments in that way. So get an array and shift it away at your desired interval. If you use the standard shell $@ array as I do above, then you'll always be working with your first two positionals $1 and $2. If you use some kind of extension array then you'll be working with either ${array[0]} and ${array[1]} or ${array[1]} and ${array[2]} depending on your shell.
Else, with a for loop you can encode some kind of delimiter into each argument:
for x in 1+2 3+4 5+6 7+8
do C="$(($x))"
done
...which actually works perfectly here, but that is usually not as cleanly done.
I could make a possible work-around (Thanks @mikeserv for providing me the idea of array):
array=('1 2' '3 4' '5 6' '7 8')
for x in "${array[@]}"
do
A=`echo $x | awk '{print $1}'`
B=`echo $x | awk '{print $2}'`
echo A=$A B=$B
C=$(($A+$B))
echo Sum,C = $C
done
Suggest if further simplification is possible.
a=(1+2 3+4 5+6 7+8); for x in "${a[@]}"; do echo "Sum,C = $((C=$x))"; done. You almost never want to call out to some other process within a loop like that. And if it's not as simple as all that, you can still split out the array members with shell param expansions like for x in "${a[@]}"; do C=$((${x% *}+${x#* }))"; done. The awk stuff is way overkill.
A and B separately to get something else, say C=A^2 and D=1-B^3. I was thinking of function statement where I can use A and B as argument $1 and $2. But I didn't try yet. :(
A=${x% *} B=${x#* }; echo "\$A=$A \$B=$B" to see what you get.
x% * and x#* do? Suppose, my set has three variables, i.e. {A,B,C}. Then could I have done in a similar fashion?
AandBand the sumC=A+B. Have modified the code a bit.