If you specify the name of a new library file in the newlibrary field, the modified library is stored under that name, and the original library is preserved under its own name.The newlibrary field specifies a name for a changed library file. You can specify a full path with the filename. LIB does not supply a default extension if you omit the extension.
You can change an existing library file by giving the name of the library file at the Library name: prompt. All operations you specify in the commands field of the command line or at the Operations: prompt are performed on that library.
LIB keeps both the unchanged library file and the newly changed version; it copies the library and makes changes to the copy. (This prevents the loss of your original file if you terminate LIB before the session is finished.) It names the two versions as follows:
If you specify the name of a new library file in the newlibrary field, the modified library is stored under that name, and the original library is preserved under its own name.
If you leave the field blank, LIB replaces the original library file with the changed version of the library and saves the original library file with the extension .BAK. Either way, at the end of a session you have two library files: the changed version and the original version.
NOTE:
You need enough space on your disk for both the original library file and the copy.