use output from one command to another command

gqk503 · 07-06-2012, 10:49 AM

I'm writing a script to take the line numbers from a command to another command such as awk. Here is what i'm trying to do. Here is what is in the animal file.
dog
cat
tiger
lion
horse
tiger
pig
grep -n "tiger" animal|cut -c 1 returns the line numbers.
3
6
I want to take those line numbers to pass it into awk to remove all the lines starting from 3 to 6. Any ideas?

grail · 07-06-2012, 11:12 AM

Ummm ... why? Just use awk from the start. To do what you already have:

Code:

awk '/tiger/{print NR}' animal

I'll let you try the next part

gqk503 · 07-06-2012, 11:48 AM

Thanks for your reply. But i don't want to just print the line number. I want to pass in the line number to another command to remove those line numbers.

grail · 07-06-2012, 12:19 PM

I think you have missed the point a little. Yes my example currently only displays the line numbers, but your original requirement was to identify lines (line numbers) using several
commands which you would then redirect to awk (somehow) and use awk to modify the file. What I have shown you is that awk has now already identified the necessary lines, so remove the
current print option and employ the changes you wished to make.

whizje · 07-06-2012, 12:20 PM

Code:

grep -n "tiger" animal | cut -c 1 | awk ...

gqk503 · 07-06-2012, 12:54 PM

I guess i wasn't very clear. Please ignore the content. My real question is how would i use an output from the first command such as this.
3
5
6
8
And use it as an input to like awk to loop through each out put.
Sorry guys if i wasn't very clear

whizje · 07-06-2012, 01:22 PM

Code:

grep -n "tiger" animal | cut -c 1 | awk ...

Use file animal as input for grep, | this is a pipe symbol that means use the output of the previous command as input for the next command. So the output of grep is piped as input for the cut command and the output of the cut command is piped as input for the awk command.

custangro · 07-06-2012, 01:34 PM

Quote:

Originally Posted by gqk503

I'm writing a script to take the line numbers from a command to another command such as awk. Here is what i'm trying to do. Here is what is in the animal file.
dog
cat
tiger
lion
horse
tiger
pig
grep -n "tiger" animal|cut -c 1 returns the line numbers.
3
6
I want to take those line numbers to pass it into awk to remove all the lines starting from 3 to 6. Any ideas?

I think sed would do what you want...

Let's say you want to delete all occurences of "tiger"

Code:

sed -e '/tiger/d' animal

But It might help us if you tell us WHAT you're trying to do, then we can help you

Give us the problem...not the solution ;-)

-C

grail · 07-07-2012, 11:54 AM

I agree with the above, you are trying to bend a solution in a direction it would seem it does not need to go. Instead of asking us to forget the input, supply input and required output
so we may assist you better.

chrism01 · 07-08-2012, 06:56 PM

As whizje has pointed out, the 'general soln' is to use the pipe operator '|' to send the output from one cmd to the input of another

Code:

cmd1 | cmd2

and you can extend that as many times as you want.

However, if you have a specific qn, then a more efficient soln may be available as per the other comments above.

HTH