Bash Snippet: Decimal to Binary Conversion

Convert a decimal value into the binary representation and vice versa in Bash using only built-ins. If you know a better way, please let me know. To ensure a properly formatted expression for the arithmetic expansion in bin2dec, the dec2bin function prefixes zeros as needed to pad to a character count evenly divisible by 8.

dec2bin () {
    num="$1"
    bin=""
    padding=""
    base2=(0 1)
    while [ "$num" -gt 0 ];
    do
            bin=${base2[$(($num % 2))]}$bin
            num=$(($num / 2))
    done
    if [ $((8 - (${#bin} % 8))) -ne 8 ]; then
            printf -v padding '%*s' $((8 - (${#bin} % 8))) ''
            padding=${padding// /0}
    fi
    echo $padding$bin
}


bin2dec () {
        echo $((2#$1))
}

Examples:

user@host:~$ dec2bin 1
00000001
user@host:~$ bin2dec 00000001
1
user@host:~$ dec2bin 255
11111111
user@host:~$ bin2dec 11111111
255
user@host:~$ bin2dec 1010101010101010
43690
user@host:~$ dec2bin 43690
1010101010101010

Perhaps not the most efficient way, but at least for small numbers it appears to be quicker than opening a subshell.

user@host:~$ time dec2bin 43690
1010101010101010

real    0m0.001s
user    0m0.000s
sys 0m0.000s
user@host:~$ time echo "obase=2;43690" | bc
1010101010101010

real    0m0.002s
user    0m0.000s
sys 0m0.000s
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2 Responses to Bash Snippet: Decimal to Binary Conversion

  1. Sz.W. says:

    function decbin {
    liczba=$1

    if [ $liczba -ge 65535 ]; then
    liczba=`expr $liczba – 65535`
    fi
    # 2B representation
    for i in 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
    do
    reszta=`expr $liczba % 2`
    wektor[i]=$reszta
    liczba=`expr $liczba / 2`
    done

    echo ${wektor[*]} | tr ‘ ‘ ”
    }

  2. Simon says:

    The dec2bin function can be simplified a fair bit.

    as follows

    dec2bin () {
    for((num=$1;num;num/=2))
    do
    bin=$((num%2))$bin
    done
    printf “%08d\n” $bin
    }

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