How to pipe a command result to a -<character><argument> option? (Without spaces)

Question

Hello! I have this set of piped commands:

grep -n '*' file.txt | head -n1 | awk -F\: '{print $1-1;}'

It tells me the previous line to that where it first find asterisks. Now I want to get the previous lines piping that to:

head -n<that previous line number>

Head requires a number following immediately the -n argument, without spaces, for example:

head -n4

How can I do that? It just won't accept adding

| head -n

at the end of the set of commands. My searches have been fruitless. Thanks!

Answer 1

You want back-ticks to substitute the value:

head -n`grep -n '*' file.txt | head -n1 | awk -F\: '{print $1-1;}'` file.txt

Or possibly something similar on multiple lines:

LINENO=`grep -n '*' file.txt | head -n1 | awk -F\: '{print $1-1;}'`
head -n${LINENO} file.txt

Answer 2

I think you could also use xargs. Something like:

grep -n '*' file.txt | head -n1 | awk -F\: '{print $1-1;}' | xargs -I % head -n% file.txt

Answer 3

Why don't you just do:

awk -- '{if (!/*/) print $0; else exit}' file.txt

or this, which is faster:

awk -- '/*/ {exit}; {print}' file.txt