I'm trying to sort out a bash command to convert a number from base 10 to an arbitrary base, using a specified set of characters (for example, to base 26 using letters a-z, although that's not actually my use-case).
I have solved this problem before, but not in bash (which I have limited experience in), and not in quite some time.
Any ideas?
I had something similar lying around, so I polished it up a bit for you
#!/bin/bash
#
# usage: convert_base <number-to-convert> <output-base> <output-digit-string>
#
# example:
# $ convert_base 3735928559 16 "0 1 2 3 4 5 6 7 8 9 A B C D E F"
# DEADBEEF
decimal_number=$1
output_base=$2
read -ra output_digits <<< "$3"
# TODO various assertions
if ((decimal_number == 0)); then
output=${output_digits[0]}
else
while ((decimal_number > 0)); do
digit=$(( decimal_number % output_base ))
output="${output_digits[digit]}$output"
decimal_number=$(( decimal_number / output_base ))
done
fi
printf '%s\n' "$output"
base 2-64 to decimal - just use built-in BASH $(( base#number ))
> echo $(( 36#B002RD3KCS ))
1117165531505356
> echo $(( 16#FF ))
255
revert conversion could be done with standard bc + helper function:
# base10 to base2..base52
# Usage: decimal_to_anybase <OtputBase> <DecimalNum>
function decimal_to_anybase()
{
BASE52=($(echo {0..9} {A..Z} {a..z})); # array of 'base_digits'
base="$1"; # output base 2..52
arg="$2"; # source decimal
res=$(bc <<< "obase=$base; $arg")
if [ "$base" -le 16 ]; then # bases 2..16 returned as is
echo "$res"
else # bases 17..52 returned as array indexes
for i in $res; do
echo -n ${BASE52[$(( 10#$i ))]} # output BASE52[base_digit]
done && echo
fi
}
> decimal_to_anybase 36 1117165531505356
B002RD3KCS
Maybe stating the obvious, but bash's printf builtin can do base 8 and 16:
$ printf '%o\n' 1234
2322
$ printf '%#o\n' 1234
02322
$ printf '%x\n' 1234
4d2
$ printf '%#x\n' 1234
0x4d2
$ printf '%X\n' 1234
4D2
$ printf '%#X\n' 1234
0X4D2
Even hexadecimal floats:
$ LC_ALL=C printf '%a\n' 1234.56
0x9.a51eb851eb851ecp+7
$ LC_ALL=C printf '%A\n' 1234.56
0X9.A51EB851EB851ECP+7
(here using LC_ALL=C to make sure the decimal radix character is .)
But it doesn't do other bases for which you'd need more advanced shells such as zsh or ksh93 or do it by hand.
To store the result in a variable:
printf -v oct %o 1234
is more efficient than:
oct=$(printf %o 1234)
Which in bash (contrary to ksh93 or the sh of some BSDs) means forking a process and send the result through a pipe.
For those who're not stuck with bash, some alternatives with some other shells can be found at:
bcor (GNU)dc. Example conversion of number1234567890to base 26 assuminga= value 0,b= 1 etc.echo 26 o 1234567890 p | dc | awk '{ for(i=1; i<=NF; i++) printf("%c",$i+97) } END { printf("\n") }'12#for base 12 in front of the numbers. E.g.echo $(( 12#100 )) $(( 12#bb ))prints144 143. Not that it helps much.)