Problem

You have many smaller pcap files that you would like to combine in to a single file

10.0.0.10_1.pcap
10.0.0.10_2.pcap
10.0.0.10_3.pcap
10.0.0.10_4.pcap
10.0.0.10_5.pcap

Solution

mergecap -a 10.0.0.10* -w output_file.pcap

Source: https://www.wireshark.org/docs/man-pages/mergecap.html