The default action of the split command on an input file is: B. It will break the file into new files of 1,000 line pieces each. The split command is used to split a file into smaller parts or chunks. By default, if no specific options are provided, the split command will split the input file into new files based on the number of lines. The default behavior of split is to create output files with a maximum of 1,000 lines each. The resulting files will be named with a default prefix "x" followed by a two-letter suffix (e.g., "xaa," "xab," "xac," and so on). To specify a different number of lines or other criteria for splitting the file, specific options can be provided with the split command.

The default action of the split command on an input file in Linux is to break the file into new files of 1,000 line pieces each. Therefore, the correct option is B. However, it is important to note that the behavior of the split command can be customized using command-line options. For example, the -b option can be used to specify the size of each output file in bytes, and the -l option can be used to specify the number of lines per output file. If no options are specified, the split command uses the default behavior of splitting the input file into 1,000 line pieces.

B is correct.