NAME

       pipexec - create a directed graph of processes and pipes

SYNOPSIS

       pipexec [OPTION]... [PROCESS DESCRIPTION]... [PIPE DESCRIPTION]...

DESCRIPTION

       pipexec creates an arbitrary network (directed graph) of processes and pipes in between - even cycles are
       possible.  It overcomes the shortcomings of shells that are typically only  able  to  create  non  cyclic
       trees.

       pipexec  also monitors all it's child processes and is able to restart the whole network of processes and
       pipes if one crashes.  Therefore pipexec can be used in SYSV-init  or  systemd  configuration  to  run  a
       network of processes.

OPTIONS

       -h     print help and version information

       -l logfd
              use  the  given  file  descriptor  for  logging.  If a 's' is specified, syslog is used.  Example:
              Specifying '2' means log to stderr.

       -p pidfile
              with pipexec it is possible to handle pipes within SYSV-init scripts.  In some environments  (e.g.
              RHEL6,  Debian7)  the  start  and stop routines need a pid file.  If this option is given, pipexec
              writes its own pid into the file shortly after start of pipexec.

       -k     if one sub-process (child) gets killed and this options is given, all other sub-processes are also
              killed.  Afterwards all processes are restarted.

       -s sleep_time
              the  time  interval  in seconds before a restart.  This option makes only sense when also the '-k'
              option is specified.

BACKGROUND

       Inside a shell it is possible to start processes and redirect the output to other processes.

       Example:
           cat Chap1.txt Chap2.txt | grep bird | wc -l

       Three processes are created: the standard output (file  descriptor  (fd)  1)  of  the  'cat'  process  is
       connected  to  the  standard  input  (fd  0) of the 'grep' command, and the standard output of the 'grep'
       command is connected to the standard input (fd 0) of the 'wc' process.

       Please note that the assignment between names and file descriptor number is pure historical  and  has  no
       technical background.

       Example:
           find / 1> >(grep .txt) 2> >(wc >/tmp/w.log)

       In  this  more complex example, the fd 1 of the 'find' process is connected to fd 0 of 'grep' and fd 2 is
       connected to fd 0 of 'wc'.

       The limitation using this way of specifying processes and pipes is, that it is not possible to  have  any
       cycles.  It is impossible to e.g. pass a fd of 'wc' either to 'grep' or to 'find'.

       pipexec  overcomes these limitations.  It makes it possible to link any two arbitrary file descriptors in
       a set of processes.

USAGE

       When building up a network of processes and pipes, there is the need to specify each element separately.

       The processes will be the nodes in the network (directed graph), the connections of the file  descriptors
       between to processes are the edges.  Each node (process) has a unique name assigned to it.  This makes it
       possible to differentiate between using the same command more than once.

       The format of specifying a process is
           [ NAME /path/to/command arg1 arg2 ... argN ]

       The first parameter 'NAME' must be a unique name.  The second parameter must be  the  full  path  of  the
       command  to  execute.   Please  note  that  always  the  full  path  must  be specified, there is no PATH
       environment variable handling (execv(2) is  used  internally  to  span  new  processes).   The  following
       parameters are the parameters passed to the command.

       The whole definition must be enclosed in square brackets.  The square brackets must be given separately -
       before and after them must be a space.

       The format of specifying a pipe between processes is
           {NAME_1:FD1>NAME_2:FD2}

       Example
           {LS:1>GREP:0}

       The names are the names of the processes, the numbers are the number of the file descriptor  that  should
       be  used  to build the pipe in between.  When using pipexec from a shell (like bash) there is the need to
       escape the brackets or use quotation marks.

EXAMPLES

       The shell command
           cat Chap1.txt Chap2.txt | grep bird | wc -l

       is equivalent to
           pipexec [ CAT /bin/cat Chap1.txt Chap2.txt ] \
             [ GREP /usr/bin/grep bird ] [ WC /usr/bin/wc -l ] \
             "{CAT:1>GREP:0}" "{GREP:1>WC:0}"

       The pipexec equivalent is longer and more complex in this example.  But pipexec can build cycles that are
       impossible within a shell:
           pipexec [ A /bin/cmd1 ] [ B /bin/cmd2 ] "{A:1>B:0}" "{B:1>A:0}"

       For more examples see the ptee(1) and peet(1) man pages.

SEE ALSO

       bash(1), ptee(1), peet(1), execv(2)

AUTHOR

       Written by Andreas Florath (andreas@florath.net)

COPYRIGHT

       Copyright  ©  2015  by Andreas Florath (andreas@florath.net).  License GPLv2+: GNU GPL version 2 or later
       <http://gnu.org/licenses/gpl.html>.