ASCII to Binary and Binary to ASCII conversion tools?

$ echo AB | perl -lpe '$_=unpack"B*"'
0100000101000010
$ echo 0100000101000010 | perl -lpe '$_=pack"B*",$_'
AB

• -e expression evaluate the given expression as perl code
• -p: sed mode. The expression is evaluated for each line of input, with the content of the line stored in the $_ variable and printed after the evaluation of the expression.
• -l: even more like sed: instead of the full line, only the content of the line (that is, without the line delimiter) is in $_ (and a newline is added back on output). So perl -lpe code works like sed code except that it's perl code as opposed to sed code.
• unpack "B*" works on the $_ variable by default and extracts its content as a bit string walking from the highest bit of the first byte to the lowest bit of the last byte.
• pack does the reverse of unpack. See perldoc -f pack for details.

With spaces:

$ echo AB | perl -lpe '$_=join " ", unpack"(B8)*"'
01000001 01000010
$ echo 01000001 01000010 | perl -lape '$_=pack"(B8)*",@F'
AB

(it assumes the input is in blocks of 8 bits (0-padded)).

With unpack "(B8)*", we extract 8 bits at a time, and we join the resulting strings with spaces with join " ".

You can use xxd to convert from ASCII and binary.

$ echo -n "A" | xxd -b
0000000: 01000001                                               A

$ echo -n "A" | xxd -b | awk '{print $2}'
01000001

Converting bases

If you're looking to do just base conversions between Hex, Octal, & Dec I usually use the basic calculator command line tool (bc) to do such things. Note that bc is always very picky about the correct order of bases: you have to specify the resulting base (obase) first, then add your choice of ibase.

$ echo "obase=2; ibase=16; A" | bc
1010

$ echo "obase=16; ibase=2; 1010" | bc
A

Using bc and bash:

#!/bin/bash

chrbin() {
        echo $(printf \\$(echo "ibase=2; obase=8; $1" | bc))
}

ordbin() {
  a=$(printf '%d' "'$1")
  echo "obase=2; $a" | bc
}

ascii2bin() {
    echo -n $* | while IFS= read -r -n1 char
    do
        ordbin $char | tr -d '\n'
        echo -n " "
    done
}

bin2ascii() {
    for bin in $*
    do
        chrbin $bin | tr -d '\n'
    done
}
ascii2bin "This is a binary message"
bin2ascii 01010100 01101000 01101001 01110011 00100000 01101001 01110011 00100000 01100001 00100000 01100010 01101001 01101110 01100001 01110010 01111001 00100000 01101101 01100101 01110011 01110011 01100001 01100111 01100101