execline
Software
skarnet.org
 The redirfd program 
redirfd redirects a given file descriptor to a file, then
executes a program.
 Interface 
     redirfd [ -r | -w | -u | -a | -x ] [ -n ] [ -b ] fd file prog...
redirfd redirects the file descriptor number fd
to file, then execs into prog....
 Options 
 One and only one of the -r, -w, -u, -a, or -x options must be given;
the -n and -b options may be added in any case.
 -  -r : open file for reading. 
-  -w : open file for writing, truncating it if it already exists. 
-  -u : open file for reading and writing. 
-  -a : open file for appending, creating it if it doesn't exist. 
-  -x : open file for writing, creating it, failing if it already exists. 
-  -n : open file in non-blocking mode. 
-  -b : change mode of file after opening it:
to non-blocking mode if the -n option was not given,
to blocking mode if it was. 
 Notes 
 -  redirfd -r n file prog... is roughly equivalent to
sh -c 'exec prog... n<file'
-  redirfd -w n file prog... is roughly equivalent to
sh -c 'exec prog... n>file'
-  redirfd -u n file prog... is roughly equivalent to
sh -c 'exec prog... n<>file'
-  redirfd -a n file prog... is roughly equivalent to
sh -c 'exec prog... n>>file'
-  redirfd -x n file prog... has no portable
shell equivalent. 
 Special fifo handling 
 The -n and -b options are especially useful with
named pipes. 
 -  Opening a fifo for reading, blocking if there is no writer:
redirfd -r n fifo prog...
-  Opening a fifo for reading, with instant success even if
there is no writer, and blocking at the first attempt to read from it:
redirfd -r -nb n fifo prog...
-  Opening a fifo for writing, blocking if there is no reader:
redirfd -w n fifo prog...
-  Opening a fifo for writing, with instant success even if
there is no reader:
redirfd -w -nb n fifo prog.... Warning:
the first attempt to write to the fifo will raise a SIGPIPE if there is
still no reader at that time. The named pipe semantics normally do not
allow a fifo to be open for writing without a reading end, and you
should know what you are doing if you're using redirfd
this way.