求解釋這個命令 time echo "scale=5000; 4*a(1)" | bc -l -q

● man bc
a (x)  The arctangent of x, arctangent returns radians.
● bc --help
usage: bc [options] [file ...]
  -h  --help         print this usage and exit
  -i  --interactive  force interactive mode
  -l  --mathlib      use the predefined math routines
  -q  --quiet        don't print initial banner
  -s  --standard     non-standard bc constructs are errors
  -w  --warn         warn about non-standard bc constructs
  -v  --version      print version information and exit