Reading from output

This is a discussion on Reading from output within the C Programming forums, part of the General Programming Boards category; I know it's probably something stupid, but, can I read a line from the stdout? I'm working under GNU/Linux....

  1. #1
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    Reading from output

    I know it's probably something stupid, but, can I read a line from the stdout? I'm working under GNU/Linux.

  2. #2
    Rabble Rouser Slacker's Avatar
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    Nope, that's asking the stream to go in the wrong direction. In some cases you can read from an output device, such as a terminal screen, by grabbing data from its buffer, but that's not really doable just with stdout.

  3. #3
    and the hat of wrongness Salem's Avatar
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    > but, can I read a line from the stdout?
    You mean like a pipe, connecting the stdout of another program to the stdin of your program?

  4. #4
    Gawking at stupidity
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    You mean something like this?
    Code:
    itsme@itsme:~/C$ cat intercept.c
    #include <stdio.h>
    #include <string.h>
    
    int main(void)
    {
      char buf[BUFSIZ], *p;
      int addnl;
    
      while(fgets(buf, sizeof(buf), stdin))
      {
        if((p = strchr(buf, '\n')))
        {
          *p = '\0';
          addnl = 1;
        }
        else
          addnl = 0;
    
        printf("Intercepted and passing on: %s\n", buf);
    
        if(addnl)
          puts(buf);
        else
          fputs(buf, stdout);
      }
    
      return 0;
    }
    Code:
    itsme@itsme:~/C$ echo "foo bar baz"
    foo bar baz
    itsme@itsme:~/C$ echo "foo bar baz" | ./intercept
    Intercepted and passing on: foo bar baz
    foo bar baz
    itsme@itsme:~/C$ cat foo.txt
    this is some text
    this is more text
    itsme@itsme:~/C$ cat foo.txt | ./intercept
    Intercepted and passing on: this is some text
    this is some text
    Intercepted and passing on: this is more text
    this is more text
    itsme@itsme:~/C$
    If you understand what you're doing, you're not learning anything.

  5. #5
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    No, it's not a pipe, anyway, I knew that it wasn't logic, but I wasn't totally sure. Thanks you anyway.

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