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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _gatk4_cmd(jvm_opts, params, data):
 """Retrieve unified command for GATK4, using 'gatk'. GATK3 is 'gatk3'. """

    gatk_cmd = utils.which(os.path.join(os.path.dirname(os.path.realpath(sys.executable)), "gatk"))
    return "%s && export PATH=%s:\"$PATH\" && gatk --java-options '%s' %s" % \
        (utils.clear_java_home(), utils.get_java_binpath(gatk_cmd),
         " ".join(jvm_opts), " ".join([str(x) for x in params]))