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   libexpect    ( 3 )

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Предостережение (Caveat)

The stream versions of the expect functions are much slower than
       the file descriptor versions because there is no way to portably
       read an unknown number of bytes without the potential of timing
       out.  Thus, characters are read one at a time.  You are therefore
       strongly encouraged to use the file descriptor versions of expect
       (although, automated versions of interactive programs don't
       usually demand high speed anyway).

       You can actually get the best of both worlds, writing with the
       usual stream functions and reading with the file descriptor
       versions of expect as long as you don't attempt to intermix other
       stream input functions (e.g., fgetc).  To do this, pass
       fileno(stream) as the file descriptor each time.  Fortunately,
       there is little reason to use anything but the expect functions
       when reading from interactive programs.

       There is no matching exp_pclose to exp_popen (unlike popen and
       pclose).  It only takes two functions to close down a connection
       (fclose() followed by waiting on the pid), but it is not uncommon
       to separate these two actions by large time intervals, so the
       function seems of little value.

       If you are running on a Cray running Unicos (all I know for sure
       from experience), you must run your compiled program as root or
       setuid.  The problem is that the Cray only allows root processes
       to open ptys.  You should observe as much precautions as
       possible:  If you don't need permissions, setuid(0) only
       immediately before calling one of the spawn functions and
       immediately set it back afterwards.

       Normally, spawn takes little time to execute.  If you notice
       spawn taking a significant amount of time, it is probably
       encountering ptys that are wedged.  A number of tests are run on
       ptys to avoid entanglements with errant processes.  (These take
       10 seconds per wedged pty.)  Running expect with the -d option
       will show if expect is encountering many ptys in odd states.  If
       you cannot kill the processes to which these ptys are attached,
       your only recourse may be to reboot.