*nix command line tips

One thing which is definitively amazing with *nix OS is that you always learn new things… Let have a look at these commands:

  • bc : a nice command-line calculator… To my mind, I’ve always considered that GUI calculator are boring to use (left clic on each number to calculate)… GNU bc provides a calculator that allows you to type in expressions for immediate calculation. It uses the standard conventions for computer arithmetic, i.e. + and – are addition and subtraction, * and / are multiplication and division, ^ is exponentiation. Juts type bc in a terminal and use it as follows:
    bc 1.06
    Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
    This is free software with ABSOLUTELY NO WARRANTY.
    For details type `warranty’.
    45*7
    315
    Parentheses can be use to set the order of evaluation (as usual)
    (20/7)^4
    16
    But, as you may have noticed, this result is “wrong”… Just because the number of digit is set to 0 by default (i.e. precision). You can change it by using the special scale variable:
    scale=2
    (20/7)^4
    65.97
    scale=5
    (20/7)^4
    66.63863
    Depending your arithmetic computation, be careful with the precision scale with some arithmetic operation (for instance, exponentiation). Finally, you can type quit to leave bc. You can do a lot of thing with bc, don’t forget to read the man page (as bc is a kind of interactive programming language), just type man bc from the command line.
  • leave : a terminal reminder… Have to leave at 15H pm ? Need to rest in 1H ? Use the leave command ! Simply type leave 1500 or leave +0100, respectively… Keep in mind that leave will continue to remind you (to leave) since you close your terminal !

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