Debugging Bash Like a Sire (2023)(blog.brujordet.no)

  %(fmt)T -output the date-time string resulting from using FMT as a format string for strftime(3)

  %(datefmt)T causes printf to output the date-time string resulting from using datefmt as a format string for strftime(3).  The corresponding argument  is  an  integer
  representing  the  number of seconds since the epoch.  Two special argument values may be used: -1 represents the current time, and -2 represents the time
  the shell was invoked.  If no argument is specified, conversion behaves as if -1 had been given.  This is an exception to the usual printf behavior.

    timestamp=$(date +'%y.%m.%d %H:%M:%S')

    printf -v timestamp '%(%y.%m.%d %H:%M:%S)T' -1

    #!/bin/bash
    
    die() {
      local frame=0
      while caller $frame; do
        ((++frame));
      done
      echo "$*"
      exit 1
    }
    
    f1() { die "*** an error occured ***"; }
    f2() { f1; }
    f3() { f2; }
    
    f3


 Output
    
    
    12 f1 ./callertest.sh
    13 f2 ./callertest.sh
    14 f3 ./callertest.sh
    16 main ./callertest.sh
    *** an error occured ***

    "${GLOBAL_VAR:-}"

    function ... {
      ...
      (( check_level >= current_level ))
    }

    return $(( check_level < current_level ))