#! /usr/bin/env bash
#
# A diff canonifier that removes all fields starting with a given
# prefix.

if [ $# != 1 ]; then
    echo "usage: $(basename $0) <field prefix>"
    exit 1
fi

awk -v "PREFIX=$1" '

BEGIN { FS="\t"; OFS="\t"; }

/^#fields/ {
    for ( i = 2; i <= NF; ++i )
        {
        if ( index($i, PREFIX) == 1 )
            rem[i-1] = 1;
        }
}

/^[^#]/ {
    for ( i in rem )
        # Mark that it is set, but ignore content.
        $i = "+";
}

{
    print;
}
'