Please provide a valid path for saving the I-TASSER library

Usage:
./download_lib.pl -libdir libdir -P true -B true -N true
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Mandatory arguments:
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-libdir template_library_directory (full path for saving the library files, such as /home/yangji/ITLIB)

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Optional arguments:
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-P  [true or false], whether to download PDB template files (default: true)
    You can set it as false if you already have modeled structure and just need function predictions
-B  [true or false], whether to download BioLiP function library files (default: true)
    You can set it as false if you do not need function predictions
-N  [true or false], whether to download the non-redundant sequence database nr (default: true)
    You can set it as false if you want to use your own nr database. (In this case, you will have to go to 
    the I-TASSER library directory, and make a soft link with the command: ln -s location_of_your_nr nr)