Bash – Convert ascii code to hexadecimal in UNIX shell script

bashshell

I'd like to convert ASCII code (like - or _ or ., etc.) to hexadecimal representation in the Unix shell (without bc command), eg : - => %2d.

Any ideas?

Best Answer

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

Related Solutions

Shell – Equivalent of Java’s String.getBytes() in Unix Shell (Cygwin)

openssl's stdin is a byte stream.

The contents of $user is a sequence of non-0 bytes (which may or may not form valid characters in UTF-8 or other character set/encoding).

printf %s "$user"'s stdout is a byte stream.

printf %s "$user" | openssl dgst -sha256 –binary

Will connect printf's stdout with openssl's stdin. openssl's stdout is another byte stream.

Now, if you're inputing $user from the user from a terminal, The user will enter it by pressing keys on his keyboard. The terminal will send corresponding characters (as written on the key label) encoded in its configured character set. Usually, that character set will be based on the character set in the current locale. You can find what that is with locale charmap.

For instance, with a locale like fr_FR.iso885915@euro, and an xterm started in that locale, locale charmap will return ISO-8859-15. If the user enters stéphane as the username, that é will likely be encoded as the 0xe9 byte because that's how it's defined in the ISO-8859-15 character set.

If you want that é to be encoded as UTF-8 before passing to openssl, that's where you'd use iconv to convert that 0xe9 byte to the corresponding encoding in UTF-8 (two bytes: 0xc3 0xa9):

IFS= read -r user # read username from stdin as a sequence of bytes
                  # assumed to be encoded from characters as per the
                  # locale's encoding
printf %s "$user" |
  iconv -t utf-8 | # convert from locale encoding to UTF-8
  openssl dgst -sha256 –binary

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

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

Best Answer

Related Solutions

Shell – Equivalent of Java’s String.getBytes() in Unix Shell (Cygwin)

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

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