关于 echo 管道符的问题

我两次执行一样的 echo 内容，但是总有一次会少个 d 字母，这是啥原因？

# echo "dis int bri" | /usr/local/sbin/microcom -s 9600 /dev/ttyUSB5 -t 1000 <WA4330-ACN>is int bri ^ % Unrecognized command found at '^' position. <WA4330-ACN> # echo "dis int bri" | /usr/local/sbin/microcom -s 9600 /dev/ttyUSB5 -t 1000 dis int bri The brief information of interface(s) under route mode: Link: ADM - administratively down; Stby - standby Protocol: (s) - spoofing Interface Link Protocol Main IP Description NULL0 UP UP(s) -- Vlan1 UP UP 192.168.1.1 WLAN-Radio1/0/1 UP UP -- WLAN-Radio1/0/2 UP UP -- WLAN-Radio1/0/3 UP UP -- The brief information of interface(s) under bridge mode: Link: ADM - administratively down; Stby - standby Speed or Duplex: (a)/A - auto; H - half; F - full Type: A - access; T - trunk; H - hybrid Interface Link Speed Duplex Type PVID Description GE1/0/1 UP 1G(a) F(a) A 1 GE1/0/2 DOWN auto A A 1 WLAN-BSS11 UP -- -- A 1 WLAN-BSS12 UP -- -- A 1 WLAN-BSS13 UP -- -- A 1 WLAN-BSS14 UP -- -- A 1 WLAN-BSS18 UP -- -- A 1 WLAN-BSS19 UP -- -- A 1