Those who have used the adb tool might have stumbled upon the following message :

$ adb logcat
     - waiting for device -
     error: more than one device and emulator

In such case, you need to find, then specify the device's serial like this :

$ adb devices -l
    List of devices attached 
    XXX900AKC2             device usb:3-1.3 product:falcon model:XT1032 device:falcon_umts
    XXXBDAD913017009       device usb:1-1   product:yakju  model:Nexus  device:maguro

$ adb logcat -s XXXBDAD913017009

Here I used the logcat command but it's the same thing when you want to install an apk or pull a file from a device.

I've just discovered that if you don't specify a serial, adb will look for an environment variable named ANDROID_SERIAL to know which device to use. If you're often using several devices in USB, you can just add the following aliases to your .bashrc file.

# ANDROID DEVICES SERIAL NUMBERS
alias adb-use-galaxy-nexus='export ANDROID_SERIAL=XXXBDAD913017009'
alias adb-use-moto-g='export ANDROID_SERIAL=XXX900AKC2'
alias reset-android-serial='unset ANDROID_SERIAL'

When using the adb logcat command, you can also set in the ANDROID_LOG_TAGS environment variable a list of tag/severity filter, like in the following example.

# suppresses all log messages except those with the tag "ActivityManager", at priority "Info" or above, and all log messages with tag "MyApp", with priority "Debug" or above
export ANDROID_LOG_TAGS="ActivityManager:I MyApp:D *:S"

These tips are fully compatible with the PidCat tool I talked about earlier.