Converting to and from hexadecimal at the command line

July 20, 2016
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As a programmer¹ I frequently need to convert numbers to or from their hexadecimal representations. Today I added the following functions to my zshrc:

function from_hex() {
    python -c "print(0x$1)"
}

function to_hex() {
    python -c "print('{:x}'.format($1))"
}

These aliases allow me to do conversions like

$ to_hex 42
2a
$ from_hex 09f91102
167317762

right from the command line. The code above works with GNU bash and with zsh.

(These functions inject unsanitized text into Python expressions, so they’re not very robust. Caveat emptor. I’m sure this is possible with shell built-ins too, but after a decade of not quite consciously realizing that I didn’t have a quick way to do these conversions, it felt good to fix the problem with a pair of one-liners that I could just type off the top of my head.)

Update (December 11, 2018): If you’re using zsh, you can do this conversion a little more safely with shell built-ins:

function from_hex() {
    typeset -i 10 x=16#$1
    print $x
}

function to_hex() {
    typeset -i 16 x=$1
    print ${(L)x#16\#}
}

That last line deserves some explanation. Zsh shows non-base-10 numbers in the format “16#100”, where 16 is the base in this example and 100 is the base-16 representation of the number. (Programmers usually prefer the notation 0x100; in base 10 this is the number 256.) The expression ${(L)x#16\#} is an example of zsh parameter expansion: starting from the value of the variable $x, the modifier #16\# strips the initial “16#” from the string and then the modifier (L) converts the result to lowercase.

Honestly, I mostly encounter hexadecimal in CSS colors. I don’t do any numerical programming.↩︎