如何在bash中将输出作为命令行参数传递？

Question

I have this two step bash command:

L=`wc -l testfile | cut -d' ' -f1`
myprogram testfile $L testfile.out

Long story short, myprogram needs the line count as an input.

I want to combine this into one line.

This does not work because using redirect | to - passes stdout stream as a file, not a string.

wc -l testfile | cut -d' ' -f1 | myprogram testfile - testfile.out

Is there a way to combine this into one line?

Answer 1

Use process substitution:

myprogram testfile $(wc -l < testfile) testfile.out
                   ^^^^^^^^^^^^^^^^^^^

This way, wc -l < testfile is evaluated together with the call of the program and you have both commands combined.

Note wc -l < file returns you just the number, so you don't have to do cut or any other thing to clean the output.