On Sunday, October 21, 2018 02:52:15 PM David Wright wrote: > On Sun 21 Oct 2018 at 13:11:16 (-0400), rhkra...@gmail.com wrote: > > <quote> > > rhk@s19:/rhk/ked1$ grep test - >| /tmp/a ; echo "and the output is" ; cat > > /tmp/a one > > two > > test > > one > > two > > test > > ^C > > rhk@s19:/rhk/ked1$ less /tmp/a > > rhk@s19:/rhk/ked1$ > > ^C is not the way to exit stdin; you should use ^D, like logging out. > Unfortunately ^C has also lost you the contents of /tmp/a as the > buffer wasn't flushed. (Use cat, rather than less, so we all see it.) > In addition, if there are any filenames following - (stdin), it will > also skip those. With ^D instead, those files will all be inspected > in the same way, in regular order, to see if they any matching lines. > No restarting required.
Ok, here is the new test (using ^D):: <quote> rhk@s19:/rhk/ked1$ grep test - >| /tmp/a ; echo "and the output is" ; cat /tmp/a one two three test one two test and the output is test test rhk@s19:/rhk/ked1$ </quote> > > > rhk@s19:/rhk/ked1$ grep -l test - >| /tmp/a ; echo "and the output is" ; > > cat /tmp/a one > > two > > test > > and the output is > > (standard input) > > rhk@s19:/rhk/ked1$ > > But now you can see that the succesful match meant that you didn't > have to keep typing any more stdin because it was closed for you > immediately after the match. > > That's the idea of "short-circuit" operations; once a match is found > in a file, the rest of it doesn't have to be read, however long the > file is. That's a useful, but non-essential, efficiency. > > But the warning is also necessary because you have to think about the > process that's feeding stdin (when it's not you typing it in). That > process might have expected stdin to remain open and writable much > longer than it did, perhaps only closing it when *it* had finished > doing whatever. Thanks -- more to absorb ;-)
