Pre-processing sentinel data for grdimage

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In case helpful for others, here is the relevant section from my bash script. The only variable that is defined outside this section is file, which is just my file prefix.

#!/bin/bash

function normalize_grid {
    # Normalize values to 0-1
    input=$1
    output=$2
    range=`gmt grdinfo ${input} -T`
    normmin=`echo $range | awk -F "[T/]" '{print $2}'`
    max=`echo $range | awk -F "[T/]" '{print $3}'`
    normmax="$((${max}-${normmin}))"
    # Normalize from 0-1
    gmt grdmath ${input} ${normmin} SUB ${normmax} DIV -V = ${output}
}

function clip_grid {
    # Clip grid values to 2-98%
    input=$1
    output=$2
    cliprange=`gmt grdinfo ${input} -T+a2`
    clipmin=`echo $cliprange | awk -F "[T/]" '{print $2}'`
    clipmax=`echo $cliprange | awk -F "[T/]" '{print $3}'`
    gmt grdclip ${input} -G${output} -Sb${clipmin}/${clipmin} -Sa${clipmax}/${clipmax} -V
}

function process_band {
    # Process band from GeoTiff image for use in grdmix, by converting all 0
    # values to NAN, clipping the tails of the distribution using an alpha value of 2,
    # and normalizing 0-1.
    # Expects:
    # - Prefix for input GeoTiff image file.
    # - Band number with 0 indexing (i.e., one less than typical band naming conventions) in format "b1".
    # Returns:
    # Filename for the processed netcdf file.
    #
    # Set variables for file names
    prefix=$1
    band=$2
    input="${prefix}.tif=gd+${band}"
    output0="${prefix}_${band}_int.nc"
    output1="${prefix}_${band}_clip.nc"
    output2="${prefix}_${band}_clip_norm.nc"
    # Convert 0 to NaN
    gmt grdmath ${input} 0 NAN = "${output0}=nf"
    # Clip to 2 and 98 percentiles
    clip_grid ${output0} ${output1}
    # Normalize values to 0-1
    normalize_grid ${output1} ${output2}
    echo ${output2}
}

red_file=`process_band ${file} "b3"`
green_file=`process_band ${file} "b2"`
blue_file=`process_band ${file} "b1"`

gmt grdmix ${red_file} ${green_file} ${blue_file} -G${file}_grdmix.tif -C
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