# Given a string describing a matrix build as Jenkins Copy-Artifacts does
# (like ANDROID_ABI=armeabi-v7a,label=ndk) on the pipeline, get the named field.
# Example: echo ANDROID_ABI=armeabi-v7a,label=ndk | getMatrixField ANDROID_ABI
# outputs armeabi-v7a to stdout.
getMatrixField() {
    tr ',' '\n' | grep "$1" | cut --only-delimited -d = -f 2
}