in reply to "Answer" questions in an interactive program?

Pretend that this is your old program asking the questions. It doesn't do anything except ask them, read the answers and print out the names it read: 

#! perl -slw
use strict;

print "enter file name  (you must specify the file name and press Ente
+r)";
chomp( my $infile = <STDIN> );

print "do you want to specify another file name (Y/N) (you must enter 
+N in most cases and press Enter)";
chomp( my $another = <STDIN> );

print "enter name for output file (you must specify a name for the out
+put file, eg ttt and press Enter)";
chomp( my $outfile = <STDIN> );

print "reading $infile; writing $outfile";

exit 99;

[download]

Then you can drive that program from perl using something like this: 

#! perl -slw
use strict;

my $progname = 'junk33';

my $pid = open CMD, '|-', $progname or die $!;

print CMD 'myInfile';
print CMD 'N';
print CMD 'myOutfile';

close CMD;

waitpid $pid, 0;

print "$progname ended: status: ", $? >>8;

[download]

And when you run that, you'll see: 

c:\test>junk32
enter file name  (you must specify the file name and press Enter)
do you want to specify another file name (Y/N) (you must enter N in mo
+st cases and press Enter)
enter name for output file (you must specify a name for the output fil
+e, eg ttt and press Enter)
reading myInfile; writing myOutfile
junk33 ended: status: 99

[download]
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
RIP an inspiration; A true Folk's Guy

Replies are listed 'Best First'.
Re^2: "Answer" questions in an interactive program?
by almut (Canon) on May 11, 2010 at 11:53 UTC 
    ...
close CMD;

waitpid $pid, 0;

print "$progname ended: status: ", $? >>8;

    [download]

    I'm a little surprised that you get the correct status value here, because close already does wait for the subprocess at the other end of the pipe (so the waitpid is neither needed nor setting the $? correctly). At least on Unix.  Does this behave differently on Windows? 

    #!/usr/bin/perl -l

my $cmd = q(perl -e 'chomp(my $ret = <STDIN>); exit $ret+1');

my $pid = open CMD, '|-', $cmd or die $!;

print CMD 98;

close CMD;
print "status from close:   ", $? >> 8;

waitpid $pid, 0;
print "status from waitpid: ", $? >> 8;

__END__
$ ./839409.pl
status from close:   99
status from waitpid: 72057594037927935

    [download]
[reply]
[d/l]
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      Does this behave differently on Windows?

      Seems so: 

      c:\test>perl
#!/usr/bin/perl -l

my $cmd = q(perl -e "chomp(my $ret = <STDIN>); exit $ret+1");

my $pid = open CMD, '|-', $cmd or die $!;

print CMD 98;

close CMD;
print "status from close:   ", $? >> 8;

waitpid $pid, 0;
print "status from waitpid: ", $? >> 8;
^Z
status from close:   99
status from waitpid: 99

      [download]
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
        It worked! Thanks a lot to all of you!
[reply]
Re^2: "Answer" questions in an interactive program?
by Anonymous Monk on May 11, 2010 at 11:08 UTC
    Thanks a lot for your time!
    I have 2 questions:
    a) The code you kindly provided should be in 2 separate programs? I put it in one perl script, correct?
    b) The old program I need to run has its executable in /usr/local/bin. Will the script need me to specify its full path?
    I tried what you wrote and returned
    enter file name  (you must specify the file name and press Enter)
Test.file
do you want to specify another file name (Y/N) (you must enter N in mo
+st cases and press Enter)
N
enter name for output file (you must specify a name for the output fil
+e, eg ttt and press Enter)
Result.file
reading Test.file; writing Result.file

    [download]
    I suppose it didn't execute the external program, right? I used your code, like:
    #! perl -slw
use strict;

print "enter file name  (you must specify the file name and press Ente
+r)";
chomp( my $infile = <STDIN> );

print "do you want to specify another file name (Y/N) (you must enter 
+N in most cases and press Enter)";
chomp( my $another = <STDIN> );

print "enter name for output file (you must specify a name for the out
+put file, eg ttt and press Enter)";
chomp( my $outfile = <STDIN> );

print "reading $infile; writing $outfile";

exit 99;

my $progname = '/usr/local/bin/simpa96';  #--->this is the name of the
+ external program I need to pass the parameters to
my $pid = open CMD, '|-', $progname or die $!;

print CMD 'myInfile';
print CMD 'N';
print CMD 'myOutfile';

close CMD;

waitpid $pid, 0;

print "$progname ended: status: ", $? >>8;

    [download]
[reply]
[d/l]
[select]

      The first program is just a substitute for your real program (which I obviously do not have), soley for the purposes of demonstration.

      You don't need it. You only need (something like) the second program.

      Does that make it clearer?

      Will the script need me to specify its full path?

      Not if it is in your path. But it will do no harm to specify the full path.

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]

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