execline
Software
skarnet.org
 The if program 
if performs conditional execution.
 Interface 
 In an execlineb script:
     if [ -X ] [ -n ] [ -t | -x exitcode ] { prog1... } prog2...
 -  if reads prog1... in a
block. It forks and executes it,
then waits for it to complete. 
-  If prog1 crashes, if prints an error message
then exits 128 plus the number of the signal that killed prog1. 
-  If prog1 exits with a non-zero code, if exits with an
approximation of that code. 
-  Else if execs into prog2. 
 Options 
 -  -X : treat a crash of prog1 as a non-zero ("false") exit. This
is mostly useful in combination with -n. 
-  -n : negate the test. If prog1 exits true, then if will
exit 1; else it will exec into prog2. 
-  -x exitcode : if if needs to exit, it will exit exitcode
instead of whatever else it would have exited. 
-  -t : if if needs to exit, it will exit 0. This is equivalent
to -x 0. 
 Notes