August 2012
Intermediate to advanced
624 pages
17h 11m
Polish
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7.3. Zakończenie wyszukiwania wynikiem typu „prawda - fałsz”
Problem
Chcemy wiedzieć, czy dany ciąg tekstowy występuje w określonym pliku. Spodziewamy się jednak odpowiedzi typu „tak — nie”, bez wyświetlania jakichkolwiek informacji z listingu wynikowego.
Rozwiązanie
Należy dodać do polecenia grep opcję –q. Dla zagwarantowania maksymalnej przenośności rozwiązania można również odrzucić dane wyjściowe przez skierowanie ich do urządzenia /dev/null. W obydwu przypadkach wynik wykonanej operacji jest zapisany w zmiennej powłoki $? odpowiadającej za przechowywanie wartości wynikowej programu. Wspomniana zmienna może być wykorzystana w instrukcji warunkowej if w następujący sposób:
$ grep –q znajdźmnie plik.danych $ if [ $? –eq 0 ] ; then echo jest ; else ...
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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.