darker.sh

        
            
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            #!/usr/bin/env bash
        
            
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            #set -x
        
            
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            darker_channel() {
        
            
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            	value=${1}
        
            
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            	light_delta=${2}
        
            
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            	result=$(echo "ibase=16; ${value} - ${light_delta}" | bc)
        
            
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            	if [[ ${result} -lt 0 ]] ; then
        
            
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            		result=0
        
            
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            	fi
        
            
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            	if [[ ${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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            darker() {
        
            
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            	hexinput=$(echo $1 | tr '[:lower:]' '[:upper:]')
        
            
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            	light_delta=${2-10}
        
            
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                a=`echo $hexinput | cut -c-2`
        
            
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                b=`echo $hexinput | cut -c3-4`
        
            
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                c=`echo $hexinput | cut -c5-6`
        
            
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            	r=$(darker_channel ${a} ${light_delta})
        
            
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            	g=$(darker_channel ${b} ${light_delta})
        
            
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            	b=$(darker_channel ${c} ${light_delta})
        
            
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            	printf '%02x%02x%02x\n' ${r} ${g} ${b}
        
            
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            }
        
            
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            darker $@
        
            
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