lazy mode in tee

[Tomáš Mudruňka]

 hello.

i was wroting small bash script which needs special behaviour of tee
and i needed to reimplement it.

The important lines looks like that:


while true; do
      cat "$2" | ccrypt -e -K "$3" | tee-lazy "$1";
done &


This code listens on named pipe $2 and when somebody writes 
something to it, it will encrypt the contents and save them to file 
$1.

But with regular tee this can't work, because tee will fopen(...,
"wb") destination file imediatelly when started when no data are 
actually coming thru pipe and it will of course delete the file 
contents right after they are written. so it should be nice to have 
something like "lazy mode", when tee opens file just after the first
byte arrives. here is my ugly alternative:




#include <stdio.h>

int main(int argc, char *argv[])
{
   if(argc < 2) {
      printf("Usage: %s output-file < input-file\n", argv[0]);
   }

   FILE *outfp;
   outfp = 0;
   unsigned int c;
   while( (c = getchar()) != EOF ) {
      if(!outfp) outfp = fopen(argv[1], "wb");
      putc(c, outfp);
 }
   fclose(outfp);
 return 0;
}




I hope there can be some similar like tee -l argument to enable 
similar functionality because handling named pipes like that is very
usefull.




Thanks. Best regards


Harvie