Time Machine progress from the command line
While the backup is running, detailed information gan be gained by 

tmutil status


which should return something like this:

Backup session status:
{
    BackupPhase = Copying;
    ClientID = "com.apple.backupd";
    DateOfStateChange = "2014-12-18 14:14:21 +0000";
    DestinationID = "B4AF88-5AD5-49BE-B254-650B44E20499";
    DestinationMountPoint = "/Volumes/TimeMachine";
    Percent = "0.852581430477103";
    Progress =     {
        TimeRemaining = 0;
        "_raw_totalBytes" = 38596759;
        bytes = 36563200;
        files = 480;
        totalBytes = 42456434;
        totalFiles = 480;
    };
    Running = 1;
    Stopping = 0;
    "_raw_Percent" = "0.9473127005301144";
}


If you only care for the percentage, try the following (looks ugly, works only if there is a percentage to display):

tmutil status | awk '/_raw_Percent/ {print $3}' | grep -o '[0-9].[0-9]\+\(e-[0-9]\+\)\?' | awk '{print $1*100}'