How to write binary data in Bash

Question

Let us say there is a variable in bash script with value \"001\" how can i write this binary data into a file as bits (as \"001\" not \"1\") echo writes it as string but i w

Answer 1

I needed this recently, someone might find it useful :

#!/bin/bash

# generate bitmasks for a C array

# loop counter
NUMBER=0
MAX_BITMASK_LENGTH=8
# max loop value : 2^8 = 255
MAXVAL=$((2**MAX_BITMASK_LENGTH))
# line number
LINE=0

# echo start of C array
echo "    const long int bitmasks[${MAX_BITMASK_LENGTH}] = {"

# loop over range of values
while [ ${NUMBER} -le ${MAXVAL} ] ; do

    # use bc to convert to binary
    BINARY=`echo -e "obase=2\n${NUMBER}"| bc`

    # print current number, linenumber, binary
    printf "%12s, /* (%i) %8s */\n" ${NUMBER} ${LINE} ${BINARY}

    # increase loop value to next value
    NUMBER=$(((NUMBER*2)+1))

    # increment line number
    LINE=$((LINE+1))
done

# echo end of C array
echo "        };"

This outputs:

$ ./generate_bitmasks.sh
    const long int bitmasks[8] = {
           0, /* (0)        0 */
           1, /* (1)        1 */
           3, /* (2)       11 */
           7, /* (3)      111 */
          15, /* (4)     1111 */
          31, /* (5)    11111 */
          63, /* (6)   111111 */
         127, /* (7)  1111111 */
         255, /* (8) 11111111 */
        };