Had to loop through numerous gzipped files that required adding a header line to them.  This script uses zcat to write in a compressed .gz file

#!/bin/bash

fname=$1
echo $fname
file_list=`find $fname -type f`
for current_file in $file_list
do
        current_dir=$(dirname "$current_file")
        echo $current_dir
        cd $current_dir
        zcat *.csv.gz | gzip > target_file.csv.a;
done