遇到了个命令：

getevent -pl 2>&1 | sed -n '/^add/h/ABS_MT_TOUCH/{x;s/[^/]*//p}'

getevent -pl 2>&1 的输出是这样的：

HWMHA:/ $ getevent -pl 2>&1
add device 1: /dev/input/event5
  name:     "huawei,touchscreen"
  events:
    KEY (0001): KEY_F1                KEY_F2                KEY_F3                KEY_F4
                KEY_F5                KEY_F7                KEY_F8                KEY_F9
                KEY_F10               KEY_F11               KEY_F12               KEY_F19
                KEY_F20               KEY_F21               KEY_F22               KEY_F23
                BTN_TOOL_FINGER       BTN_TOUCH
    ABS (0003): ABS_X                 : value 40, min 0, max 1079, fuzz 0, flat 0, resolution 0
                ABS_Y                 : value 210, min 0, max 1919, fuzz 0, flat 0, resolution 0
                ABS_PRESSURE          : value 0, min 0, max 255, fuzz 0, flat 0, resolution 0
                ABS_MT_TOUCH_MAJOR    : value 0, min 0, max 15, fuzz 0, flat 0, resolution 0
                ABS_MT_WIDTH_MAJOR    : value 0, min 0, max 100, fuzz 0, flat 0, resolution 0
                ABS_MT_WIDTH_MINOR    : value 0, min 0, max 100, fuzz 0, flat 0, resolution 0
                ABS_MT_POSITION_X     : value 0, min 0, max 1079, fuzz 0, flat 0, resolution 0
                ABS_MT_POSITION_Y     : value 0, min 0, max 1919, fuzz 0, flat 0, resolution 0
                ABS_MT_TRACKING_ID    : value 0, min 0, max 15, fuzz 0, flat 0, resolution 0
                ABS_MT_PRESSURE       : value 0, min 0, max 255, fuzz 0, flat 0, resolution 0
  input props:
    INPUT_PROP_DIRECT
could not get driver version for /dev/input/mouse0, Not a typewriter
add device 2: /dev/input/event2
  name:     "hisi_on"
  events:
    KEY (0001): KEY_POWER
  input props:
    <none>
add device 3: /dev/input/event1
  name:     "hisi_gpio_key"
  events:
    KEY (0001): KEY_VOLUMEDOWN        KEY_VOLUMEUP
  input props:
    <none>
add device 4: /dev/input/event3
  name:     "fingerprint"
  events:
    KEY (0001): KEY_ENTER             KEY_SEMICOLON         KEY_GRAVE             KEY_LEFTSHIFT
                KEY_Z                 KEY_V                 KEY_N                 KEY_UP
                KEY_LEFT              KEY_RIGHT             KEY_DOWN              KEY_INSERT
                KEY_DELETE            KEY_MUTE              KEY_EXIT
  input props:
    <none>
add device 5: /dev/input/event4
  name:     "hi3660_HI6403_CARD Headset Jack"
  events:
    KEY (0001): KEY_VOLUMEDOWN        KEY_VOLUMEUP          KEY_F14               KEY_MEDIA
    SW  (0005): SW_HEADPHONE_INSERT   SW_MICROPHONE_INSERT
  input props:
    <none>
add device 6: /dev/input/event0
  name:     "soundtrigger_input_dev"
  events:
    KEY (0001): KEY_F14               KEY_F15               KEY_F16               KEY_F17
                KEY_F18
  input props:
    <none>
could not get driver version for /dev/input/mice, Not a typewriter

那 sed -n '/^add/h/ABS_MT_TOUCH/{x;s/[^/]*//p}' 是干啥的呢？

1. 首先找到以 add 开始的行，然后把这一行保存下来 h 就是干这个事情的。
2. 再往下找 ABS_MT_TOUCH，找到了通过 x 把前面保存的 h，替换过来。x 就是干这个事情。
3. s/[^/]*//p 是把替换过来的 add device 1: /dev/input/event5，把到第一个 / 位置的字符串替换为空，就变成了 /dev/input/event5
4. 2 和 3 两个命令用分号 ; 隔开。