If not writing to stdout, xxd writes into its output file without truncating it. Additional Whitespace and line-breaks are allowed anywhere. Default is lower case. If the ouput file is seekable, then the linenumbers at the start of each hexdump line may be out of order, lines may be missing, or overlapping. If the output file is not seekable, only gaps are allowed, which will be filled by null-bytes.
Garbage is silently skipped.
Here an thing that looks like a pair of hex-digits is interpreted. Hexdump this file with autoskip. Create a 1 byte file containing a single 'A' character. 1 error while parsing options. 2 problems with input file. .