linux AWK

$ cat 1.txt
./smp_ao_stafpotl_info.log.2020-07-23-AM:2020-07-23 09:36:22,655 898582491 [WebContainer : 1] ERROR com.group.bussvc.stafpotl.service.AppListTypeService - 20699052 saveESignature:780-000005-932


45101279@A156A0L62J8EDA8 MINGW64 /
$ awk 'BEGIN {FS="_"} {print $2}' 1.txt
ao

45101279@A156A0L62J8EDA8 MINGW64 /
$ awk -F '_' '{print $2}' 1.txt
ao

这两者是等同得