Redirect output to stdout and pipe to a binary

You can use tee and process substitution for this:

cat file.txt | tee >(pbcopy) | grep errors

This will send all the output of cat file.txt to pbcopy, and you'll only get the result of grep on your console.

You can put multiple processes in the tee part:

cat file.txt | tee >(pbcopy) >(do_stuff) >(do_more_stuff) | grep errors

You are confusing two very different types of inputs.

1. Standard input (stdin)
2. Command line arguments

These are different, and are useful for different purposes. Some commands can take input in both ways, but they typically use them differently. Take for example the wc command:

1. Passing input by stdin:

   ls | wc -l
   

   This will count the lines in the output of ls

2. Passing input by command line arguments:

   wc -l $(ls)
   

   This will count lines in the list of files printed by ls

Completely different things.

To answer your question, it sounds like you want to capture the rate from the output of the first command, and then use the rate as a command line argument for the second command. Here's one way to do that:

rate=$(command1 | sed -ne 's/^rate..\([0-9]*\)%.*/\1/p')
command2 -t "rate was $rate"

Explanation of the sed:

• The s/pattern/replacement/ command is to replace some pattern
• The pattern means: the line must start with "rate" (^rate) followed by any two character (..), followed by 0 or more digits, followed by a %, followed by the rest of the text (.*)
• \1 in the replacement means the content of the first expression captured within \(...\), so in this case the digits before the % sign
• The -n flag of the sed command means to not print lines by default. The p at the end of the s/// command means to print the line if there was a replacement. In short, the command will print something only if there was a match.