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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 get_sort_cmd(tmp_dir=None):
 """Retrieve GNU coreutils sort command, using version-sort if available. Recent versions of sort have alpha-numeric sorting, which provides more natural sorting of chromosomes (chr1, chr2) instead of (chr1, chr10). This also fixes versions of sort, like 8.22 in CentOS 7.1, that have broken sorting without version sorting specified. https://github.com/bcbio/bcbio-nextgen/issues/624 https://github.com/bcbio/bcbio-nextgen/issues/1017 """

    has_versionsort = subprocess.check_output("sort --help | grep version-sort; exit 0", shell=True).strip()
    if has_versionsort:
        cmd = "sort -V"
    else:
        cmd = "sort"
    if tmp_dir and os.path.exists(tmp_dir) and os.path.isdir(tmp_dir):
        cmd += " -T %s" % tmp_dir
    return cmd