Perl's diamond operator: can it be done in bash?

Question

Is there an idiomatic way to simulate Perl's diamond operator in bash? With the diamond operator,

script.sh | ...

reads stdin for its input and

script.sh file1 file2 | ...

reads file1 and file2 for its input.

One other constraint is that I want to use the stdin in script.sh for something else other than input to my own script. The below code does what I want for the file1 file2 ... case above, but not for data provided on stdin.

command - $@ <<EOF
some_code_for_first_argument_of_command_here
EOF

I'd prefer a Bash solution but any Unix shell is OK.

Edit: for clarification, here is the content of script.sh:

#!/bin/bash
command - $@ <<EOF
some_code_for_first_argument_of_command_here
EOF

I want this to work the way the diamond operator would work in Perl, but it only handles filenames-as-arguments right now.

Edit 2: I can't do anything that goes

cat XXX | command

because the stdin for command is not the user's data. The stdin for command is my data in the here-doc. I would like the user data to come in on the stdin of my script, but it can't be the stdin of the call to command inside my script.

Answer 1

Sure, this is totally doable:

#!/bin/bash
cat $@ | some_command_goes_here

Users can then call your script with no arguments (or '-') to read from stdin, or multiple files, all of which will be read.

If you want to process the contents of those files (say, line-by-line), you could do something like this:

for line in $(cat $@); do
    echo "I read: $line"
done

Edit: Changed $* to $@ to handle spaces in filenames, thanks to a helpful comment.

Answer 2

Kind of cheezy, but how about

cat file1 file2 | script.sh