Courses/Computer Science/CPSC 457.W2012/FIFO Example

$ echo "hello" > hello.txt

$ cat hello.txt 
hello
$ tail -f hello.txt &
[1] 3983
$ hello 

$ echo "goodbye" > hello.txt
goodbye
$ ps
  PID TTY           TIME CMD
 3949 ttys006    0:00.03 -bash
 3983 ttys006    0:00.00 tail -f hello.txt
$ 

Pipes

$ history | gawk '{print $2}' | head
make
emacs
make
emacs
make
emacs
make
emacs
make
ls
$ history | gawk '{print $2}' | sort | head
PS1="$
bunzip2
bunzip2
cat
cd
cd
cd
cd
cd
cd
$ history | gawk '{print $2}' | sort | uniq -c | head
  1 PS1="$
  2 bunzip2
  1 cat
 76 cd
 31 clear
  3 cp
  2 dot
  3 echo
 29 emacs
 20 exit
$ history | gawk '{print $2}' | sort | uniq -c | sort -nr | head
100 ls
 76 cd
 37 ssh
 31 clear
 29 emacs
 21 man
 20 exit
 19 open
 18 more
 14 mkdir

Named Pipes (FIFOs) Named pipes provide a way of creating an I/O FIFO buffer, represented by a file, that can be referred to by name in other operations, scripts, and programs. The command-line pipes we encountered above are somewhat anonymous; we cannot refer to the pipe at stage three above, for example. It simply exists to pass output from sort to uniq

$ mkfifo pipeline
$ ls
hello.txt	pipeline|	plan.txt	plan.txt~
$ tail -f pipeline &
[1] 4153
$ cat hello.txt > pipeline 
goodbye
$ fg
tail -f pipeline
^C
$ cat hello.txt