August 2012
Intermediate to advanced
624 pages
17h 11m
Polish
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2.10. Dodawanie danych wyjściowych zamiast nadpisywania ich
Problem
Każde przekierowanie danych wyjściowych powoduje ponowne utworzenie pliku. Co zrobić, jeśli dane są przekierowywane po raz drugi (lub trzeci lub...), a poprzednie informacje nie mogą zostać utracone?
Rozwiązanie
Symbol podwojonego znaku większości (>>) jest operatorem przekierowania w powłoce bash oznaczającym dołączenie danych wyjściowych.
$ ls > /tmp/ls.txt $ cd ../gdzieś $ ls >> /tmp/ls.txt $ cd ../inny_katalog $ ls >> /tmp/ls.txt $
Analiza
Pierwsza instrukcja wykonuje operację przekierowania polegającą na usunięciu pliku, jeśli ten istnieje, i utworzeniu nowego, w którym zostanie zapisany wynik polecenia ls.
W drugim i trzecim wywołaniu instrukcji ls uwzględniony został podwójny ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
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.