Looping in Hex
for i in `seq 1 10`; do echo $i; done
However, seq can only handle decimal (base 10) input arguments. What if I want seq to do stuff in hex (base 16), eg. loop from 00 to FF in step of 5. At first I was thinking of creating two functions (hex2dec and dec2hex) so that I can do this:
- input arguments in hex convert to decimal (use hex2dec)
- increment the looping counter in decimal
- convert any ouput to hex (use dec2hex)
The above steps work fine but it will involve too many processes to be forked out from the parent shell. Although I was using bc (arbitrary precision calculator language) to do conversion between base10 and base16, I did not explore the looping within the bc.
Do you know that bc language provides "for" loop construct ? Now I can bring my loop out of the shell script into bc and I do not have to do any counter increment. Since bc cannot handle both ibase=16 and obase=16 together, I need to convert the input hex number to decimal and let bc to work out all the output in hex. I even include an optional -w flag to equalise the width by padding with leading zeroes.
Here is my seq2hex.sh
#! /bin/sh
hex2dec()
{
hex=`echo $1 | tr '[a-z]' '[A-Z]'`
echo "ibase=16;$hex" | bc
}
usage()
{
echo "Usage: $0 [-w width] start end"
echo "Usage: $0 [-w width] start step end"
}
width=""
while getopts w: c
do
case $c in
w) width=$OPTARG ;;
\?) usage; exit 1 ;;
esac
done
shift `expr $OPTIND - 1`
# input arguments in hex, convert to decimal
if [ $# -eq 2 ]; then
start=`hex2dec $1`
end=`hex2dec $2`
step=1
elif [ $# -eq 3 ]; then
start=`hex2dec $1`
step=`hex2dec $2`
end=`hex2dec $3`
else
usage
exit 2
fi
echo "obase=16; for(i=$start;i<=$end;i+=$step) { i }" | \
bc | \
awk '{printf("%0'$width's\n",$1)}'
seqhex.sh in action:
$./seqhex.sh Usage: ./seqhex.sh [-w width] start end Usage: ./seqhex.sh [-w width] start step end $./seqhex.sh 6 F 6 7 8 9 A B C D E F $./seqhex.sh AA BB AA AB AC AD AE AF B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 BA BB $./seqhex.sh AA 5 BB AA AF B4 B9 $./seqhex.sh -w 4 AA 5 BB 00AA 00AF 00B4 00B9
Labels: bc, shell script
posted by chihungchan at 8:06 AM
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