how to redirect multiple input files?

Shell Programming and Scripting
1

I have a program that runs like "cat f1 - f2 -", I need to write shell script to run the program whose standard input will be redirected from 2 files. I spend a whole day on it, but didn't figure out. Can someone help me out? Thanks!

2

not exactly sure what your requirement is, but it sounds like:

redirect standard in from 2 files at the same time to a single process

that is done like this:

cat f1 f2|process

or this

process<cat f1 f2

'cat' concatenates the files, so this is nearly equivalent to the following:

process < f1
process < f2
3

Thanks for your reply. But it still does not work. It says "cat: No such file or directory".
My program command can run like this: "./a.out file1.txt - file2.txt -", when the parameter is a file name, it will read file content, otherwise, when the parameter is a hyphen, it will read from stdin(just like "cat file1 - file2 -"). I need write a test script to run this program, however, I don't know how to redirect two file for stdin. Anybody can help me? Thanks.

4

can you post your script?

the error means that one of the arguments you are passing to 'cat' is not a file, or doesn't exist on the path you've indicated--however without seeing how you are calling 'cat' in your script, I can only speculate.

5

the code you have is treating cat as a file name.

process<cat f1 f2

to use this method you will need to do it in two steps

cat f1 f2 >/tmp/foo
process</tmp/foo

I don't really understand the requirements so I am not sure how to provide a solution. Having parameters like <file1> <-> <file2> <-> just does not seem right. What is the end result you are looking for?

6

You cannot redirect from a command with <; the argument must be a file.

If your shell has process substitution, you can do:

process < <(cat f1 f2)

Or use a here document:

process <<.
$( cat f1 f2 )
.
7

good point cfa. thx.

8

Thanks. But I still do not know how to resolve the problem.
The program is launched by following command,

prog file1 - file2 -

When I enter the command, it will process file1, and then read from stdin(-) until I enter Ctrl D. and then process file2, and then read from stdin(-) until Ctrl D.

I can embed the data from stdin into shell script. How do I do this in the script without any interactive input? Because there are two EOF, perhaps I also can not use here doc. Struglling for 2 days... Thanks.

9

You could try putting a ^D in the here document (in vi by entering Ctrl-v followed by Ctrl-d) and see if that works, otherwise perhaps an expect script may be a better way to go.