[TriLUG] confessions of a bash junky: the mkfifo command

[jonc at nc.rr.com]

I write a lot of scripts. I mean a LOT of scripts. If I can solve a problem in 10 to 15 minutes by throwing it into a bash script, then that's what happens. So I *love* bash... unabashedly.

I recently ran across an old command 'mkfifo" and tilted my head as I wondered once more, what the heck this does...  In earlier days I had stared at the man pages for mkfifo with blinking eyes and then moved on... thinking that perhaps one day I might be wise enough to comprehend this technical soup before me, but not that day... No my friend - not that day, but *this* day!  

Below are my notes on using 'mkfifo'. Submitted for your diversion.

# You can use the mkfifo command to create an input/output pipe (or buffer)
# Feed info into the pipe using one process, pull info out of the pipe
# using another processes...
#
# Make the pipe:
mkfifo imapipe
# The pipe is created in the current directory and looks and acts like a file
# (doesn't everything in Unix?)
#
# Feed info into the pipe. In this case the output from the find command.
find /home/jonc >imapipe
#
# Note: the script stays frozen here till the pipe is cleared
#
####
# Another process runs and pulls from the pipe
cat imapipe
#
# Note: this clears the buffer (or pipe) and the previous script now continues
#
# Note2: you can grab from the pipe first - which causes that script
#   to wait for input. Then when the first script runs and loads the buffer
#   the second script immediately pulls the data out and continues to process.
#   So this can be used as a timer to co-ordinate scripts..
#   to wait for input, or
#   to wait for output
#   from another script or process.
#
# Note3: Multiple processes can put information into the buffer - the info
#   stacks up and comes out First In -> First Out
#   When a process pulls from the buffer, it gets everything in the buffer
#   and the other processes that loaded the buffer all continue.
#   An interesting way to set off multiple scripts simultaneously

Jon "bash me" Carnes