Bourne-Again shell script, ASCII text executable
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#!/usr/bin/env bash
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set -ueo pipefail
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#set -x
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mix_channel() {
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value1="$(printf '%03d' "0x$1")"
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value2="$(printf '%03d' "0x$2")"
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ratio="$3"
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result="$(bc <<< "scale=0; ($value1 * 100 * $ratio + $value2 * 100 * (1 - $ratio)) / 100")"
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if [[ "$result" -lt 0 ]]; then
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result=0
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elif [[ "$result" -gt 255 ]]; then
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result=255
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fi
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echo "$result"
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}
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mix() {
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hexinput1="$(tr '[:lower:]' '[:upper:]' <<< "$1")"
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hexinput2="$(tr '[:lower:]' '[:upper:]' <<< "$2")"
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ratio="${3-0.5}"
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a="$(cut -c-2 <<< "$hexinput1")"
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b="$(cut -c3-4 <<< "$hexinput1")"
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c="$(cut -c5-6 <<< "$hexinput1")"
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d="$(cut -c-2 <<< "$hexinput2")"
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e="$(cut -c3-4 <<< "$hexinput2")"
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f="$(cut -c5-6 <<< "$hexinput2")"
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r="$(mix_channel "$a" "$d" "$ratio")"
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g="$(mix_channel "$b" "$e" "$ratio")"
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b="$(mix_channel "$c" "$f" "$ratio")"
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printf '%02x%02x%02x\n' "$r" "$g" "$b"
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}
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mix "$@"
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