Bash – Convert a value into a “Binary Number” in a shell script

bashshell

I know of bc:

$> var="304"
$> echo "obase=2; $var" | bc
100110000

Could it be done in shell (no external call)?

This question:
Binary to hexadecimal and decimal in a shell script
Asks how to convert FROM binary, not TO a binary number.

The answers there deal either with binary byte (as opposed to binary number, i.e.: a base-2 number) using xxd, or some other external tool. So, no, this question is not a duplicate of that.

Best Answer

In bash:

toBinary(){
    local n bits sign=''
    (($1<0)) && sign=-
    for (( n=$sign$1 ; n>0 ; n >>= 1 )); do bits=$((n&1))$bits; done
    printf "%s\n" "$sign${bits-0}"
}

Use:

$> toBinary 304
100110000

Or more POSIX_ly:

toBinaryPOSIX(){
    n=$(($1))
    bits=""
    sign=""
    if [ "$n" -lt 0 ]; then
        sign=- n=$((-n))
    fi
    while [ "$n" -gt 0 ]; do
        bits="$(( n&1 ))$bits";
        : $(( n >>= 1 ))
    done
    printf "%s\n" "$sign${bits:-0}"
}

Use:

$> toBinaryPOSIX 304
100110000

If Value is hex:

$> toBinaryPOSIX 0x63
1100011

Related Solutions

Bash – Convert ascii code to hexadecimal in UNIX shell script

There's a printf tool that simulates the C function; normally it's at /usr/bin/printf, but a lot of shells implement built-ins for it as well. You can use %02x to get the hex representation of a character, but you need to make sure you pass a string that includes the character in single-quotes (Edit: It turns out just a single-quote at the beginning is sufficient):

printf "%%%02x\n" "'-"   # Outputs %2d

You can make a shell function for convenience:

function hex() {
    printf "%%%02x\n" "'$1"
}

hex -   # Outputs %2d
hex _   # Outputs %5f
hex .   # Outputs %2e

Bash – how to convert number to time format in shell script

BASH isn't that bad for this problem. You just need to use the very powerful, but underused date command.

for i in {1..10}; do
  hrmin=$(date -u -d@$(($i * 10 * 60)) +"%H:%M")
  outfile=${hrmin/:/-}.mp4
  ffmpeg -i video.mp4 -ss ${hrmin}:00 -t 00:10:00 -c copy ${outfile}
done

`date` Command Explained

date with a -d flags allows you to set which date you want displayed (instead of the current date and time, which is the default). In this case, I am setting it to a UNIX time by prepending the @ symbol before an integer. The integer in this case is the time in ten minute increments (calculated by the BASH built-in calculator: $((...))).

The + symbol tells date that you would like to specify a format for displaying the results. In our case, we care only about the hour (%H) and the minutes (%M).

And finally, the -u is to display as UTC time instead of local. This is important in this case because we specified the time as UTC when we gave it the UNIX time (UNIX time is always as UTC). The numbers would most likely not start from 0 if you didn't specify -u.

BASH Variable Substitution Explained

The date command gave us just what we needed. But colons in a file name might be problematic/non-standard. So, we substitute the ':' for a '-'. This can be done by the sed or cut or tr command, but because this is such a simple task, why spawn a new subshell when BASH can do it?

Here we use BASH's simple expression substitution. To do this, the variable must be contained within curly braces (${hrmin}) and then use the standard forward slash notation. The first string after the first slash is the search pattern. The second string after the second slash is the substitution.

BASH variable substitution and more can be found at http://tldp.org/LDP/abs/html/parameter-substitution.html.