August 2012
Intermediate to advanced
624 pages
17h 11m
Polish
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6.1. Wykonywanie działań arytmetycznych w skrypcie powłoki
Problem
Podczas wykonywania kodu skryptu muszą zostać zrealizowane pewne nieskomplikowane operacje arytmetyczne.
Rozwiązanie
Do wyznaczania wartości wyrażenia arytmetycznego (bazującego na liczbach całkowitych) wykorzystuje się zapis $(( )) lub instrukcję let.
COUNT=$((COUNT + 5 + MAX * 2)) let COUNT+=5+MAX*2
Analiza
Jeśli definiowane przez programistę działania są operacjami na liczbach całkowitych, można wykorzystywać wszystkie standardowe operatory (właściwe dla języka C), zapisując je wewnątrz konstrukcji $(( )). Powłoka bash udostępnia jeden dodatkowy operator ** — odpowiada ona za podnoszenie liczby do określonej potęgi (np. wykonanie instrukcji MAX=$((2**8)) powoduje przypisanie zmiennej ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.