Shell Programming and Scripting

I want to use a content of a file as standard input to a program and dump the output to a file. However, when I try the following code:

Code:

./program < input.in > output.out

The output.out is empty. So, how can I handle this problem?
Thanks in advance!

What does ./program do? What is in input.in?

'program' is the name of the script I want to run. The parameters of this script is in the input.in file. After running that script, the results are dumped into output.out file.

Have you made sure the output is going to stdout? It might be going to stderr instead. If this is the case modify your statement like this:

Code:

./program < input.in 2> output.out

or this (stdout and stderr combined):

Code:

./program < input.in > output.out 2>&1

In general a UNIX process acts like a (Y-shaped) garden hose: you put something into stdin, the process does something with this input and outputs something at stdout (usually the result of its "normal" operation) and something at stderr (usually error/diagnostic messages). You can redirect where stdout goes with "[1]>" and where stderr goes with "2>". There are also other I/O-channels which can be used, but these three (0=stdin, 1=stdout, 2=stderr) are most commonly used. I/O-descriptor "X" can be redirected with "X>" and to redirect I/O-descriptor "X" where "Y" already points to is done with "X>&Y".

I hope this helps.

bakunin

Generalities don't help.
If ./program contains:

Code:

grep -v "="

and input.in contains:

Code:

a1=123
a2=234

then the command:

Code:

./program < input.in > output.out

will create output.out as an empty file.
If ./program contains:

Code:

cat

and input.in is not an empty file, then output.out will not be an empty file.

I repeat: What does ./program do? What is in input.in?

I am sorry, I can't understand why

Code:

./program < input.in > output.out

redirects the outputs to

Code:

stderr

? And I also tried the following code:

Code:

./program `cat input.in` > output.out

This time, it works well, however, does this script take the parameters from standard input this time?
What the differences between this code and the

Code:

./program < input.in > output.out

?

Your program requires command line parameters. This has nothing to do with stdin.
"program" will contain some references to $1, $2,... and those are populated when you call it like this:

Code:

./program value1 value2

That's what your experiment with cat evaluated to.

If "program" would ask you for some values after you started it you could redirect the values like in your original post.