Print the given git hash + a prepended "1" in decimal form

decimalize_git_hash.bash

#!/bin/bash -euo pipefail

if [ ${#} -eq 0 ]
then
# read from STDIN
MAYBE_GIT_HASH=$( cat )
else
MAYBE_GIT_HASH="${1}"
fi

LEGAL_GIT_HASH_CHARACTERS="0123456789ABCDEFabcdef"
# grep regex doesn't allow + metacharacter :(
HASH_GREP_REGEX='^['"${LEGAL_GIT_HASH_CHARACTERS}"']['"${LEGAL_GIT_HASH_CHARACTERS}"']*$'
GIT_HASH=$( echo "${MAYBE_GIT_HASH}" | grep "${HASH_GREP_REGEX}" ) || {
echo "\"${MAYBE_GIT_HASH}\" doesnt look like a git hash. A git hash should have only: \"${LEGAL_GIT_HASH_CHARACTERS}\"" >&2
exit 1
}

# We must prefix the git hash with a 1
# If it starts with a zero, when we decimalize it,
# and later hexify it, we'll lose the zero.
ONE_PREFIXED_GIT_HASH=1"${GIT_HASH}"

# bc requires hex to be uppercase because
# lowercase letters are reserved for bc variables
UPPERCASE_ONE_PREFIXED_GIT_HASH=$( echo "${ONE_PREFIXED_GIT_HASH}" | tr "[:lower:]" "[:upper:]" )

# convert to decimal
# See "with bc": http://stackoverflow.com/a/13280173/9636
echo "ibase=16;obase=A;${UPPERCASE_ONE_PREFIXED_GIT_HASH}" | bc

There's an easier way to convert git hashes to decimal. I have included my method for collecting the hash from git as well:

IFS="v-." read empty major minor patch distance hash <<<"$(git describe)"
# so if `git describe` returns v1.8.21-41-gc0ffee1, this will produce the following variables:
# empty | major | minor | patch | distance | hash
#       | 1     | 8     | 21    | 41       | gc0ffee1

# Add the one like you did above, for completeness' sake, and remove the 'g' prefix in one fell swoop:
hash="${hash/g/1}"

# Generate the decimal representation
printf "%d" 0x$hash

Or, in condensed form:

IFS="v-." read empty major minor patch distance hash <<<"$(git describe)"
printf "%d" 0x"${hash/g/1}"

EDIT: One final revision, using the method you use for getting the hash (pays to keep reading!):

hash=$(git rev-parse --short=7 HEAD)
printf "%d" 0x1"${hash}"

Condense it even more:

printf "%d" 0x1"$(git rev-parse --short=7 HEAD)"

Not all distributions/BSDs/etc come withbcpre-installed, but even busybox's ash hasprintf.

There's an easier way to convert git hashes to decimal. I have included my method for collecting the hash from git as well:

IFS="v-." read empty major minor patch distance hash <<<"$(git describe)"
# so if `git describe` returns v1.8.21-41-gc0ffee1, this will produce the following variables:
# empty | major | minor | patch | distance | hash
#       | 1     | 8     | 21    | 41       | gc0ffee1

# Add the one like you did above, for completeness' sake, and remove the 'g' prefix in one fell swoop:
hash="${hash/g/1}"

# Generate the decimal representation
printf "%d" 0x$hash

Or, in condensed form:

IFS="v-." read empty major minor patch distance hash <<<"$(git describe)"
printf "%d" 0x"${hash/g/1}"

EDIT: One final revision, using the method you use for getting the hash (pays to keep reading!):

hash=$(git rev-parse --short=7 HEAD)
printf "%d" 0x1"${hash}"

Condense it even more:

printf "%d" 0x1"$(git rev-parse --short=7 HEAD)"

Not all distributions/BSDs/etc come withbcpre-installed, but even busybox's ash hasprintf.

@thirdwheel how do you reverse the process?

didnt realize its just hex to dec conversion, got it echo "obase=16; 348379070" | bc

@thirdwheel how do you reverse the process?

@andrewvmail sorry for the late reply, see below.

$ printf "%d" 0xd3ac43f
221955135
$ printf "0x%x" 221955135
0xd3ac43f

thanks!

…

On Mon, Aug 5, 2019 at 4:44 PM Aaron Mason ***@***.***> wrote: @thirdwheel <https://github.com/thirdwheel> how do you reverse the process? @andrewvmail <https://github.com/andrewvmail> sorry for the late reply, see below. $ printf "%d" 0xd3ac43f 221955135 $ printf "0x%x" 221955135 0xd3ac43f — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <https://gist.github.com/87eecb5874169f76cfacb26dc4223575?email_source=notifications&email_token=AASRS6XVW3QZVI5G2K5ASWTQDC3PBA5CNFSM4IJPWFD2YY3PNVWWK3TUL52HS4DFVNDWS43UINXW23LFNZ2KUY3PNVWWK3TUL5UWJTQAFWRDY#gistcomment-2990652>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AASRS6S55NCQFID62CMGIWDQDC3PBANCNFSM4IJPWFDQ> .

Very interesting, @andrewvmail! Thanks for the alternative and way cleaner way to do this.

One single caveat about your technique is that that method can't decimalize the whole hash, only the short (7-char) ones. But I think we're all using only the hash prefix, so it's not a big deal 😁