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Extract a specific line from a stream

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# 1  
Old 01-08-2011
Error Extract a specific line from a stream
Hello,

I'm trying to code a bash script and I was wondering how to extract a specific line from a stream.

E.g.
My file "file" contains three lines and i'd like to find a function f which returns after execution a specific line like the second line, which would be :

Code:
f(file, 2) = Second line of the file (String form)



I was trying to make so with grep, less, cat, more, ... but I can't figure oout any way to make it happens.

Ok to be more precise, I wanna print the name of the n-file in the "ls -1" stream. For example if I type "ls -1", here's the output:

Code:
file1
file2
file3



My script prompts the user to specify the name of the file n he wants to read.
If the user type 2, the new output would be "file2" (string form).
The final line instruction would be something like :

Code:
f( $(ls -1) , n) = the n-line of the output of "ls -1"


Ok so much lines for a little trouble.
I hope someone knows a solution for it, and since i'm french and i'm not sure my problem is well-posted feel free to ask other questions.

Thanks Smilie
# 2  
Old 01-08-2011
Try this bash code:
Code:
f()
{
  local i
  while IFS= read -r line
  do 
    if [[ $((i+=1)) -eq $2 ]]; then  
      printf "%s\n" "$line"
      break
    fi
  done < "$1"
}

Call it like this:

Code:
f  file 2

or
Code:
f <(ls -1) n # = the n-line of the output of "ls -1"

Last edited by Scrutinizer; 01-08-2011 at 01:46 PM..
This User Gave Thanks to Scrutinizer For This Post:
Oddant
# 3  
Old 01-08-2011
Nope sorry that doesn't seem to work or perhaps i'm doing it the wrong way.
does it not already exist a unix command ?

ok i've found the line function but this function seems to return the first line of any stream.
Besides maybe i'm using it badly.

anyway thanks for your help, but when I type "f <(ls -1) 2" nothing happening, is that working on your system?
# 4  
Old 01-08-2011
Hi, I thought you were looking for a bash function. You need to run the function code first in a bash shell and then call it, or put it in a bash script.
Sure there are commands that can do this:
Code:
sed -n 2p file

for example, or more efficiently:
Code:
sed '2q;d' file

Last edited by Scrutinizer; 01-08-2011 at 01:44 PM..
This User Gave Thanks to Scrutinizer For This Post:
Oddant
# 5  
Old 01-08-2011
Ok it works perfectly, what a pleasure to end up with what we looking for.

Thanks a lot having helped me ! Smilie

Regards, Oddant
Last edited by Oddant; 01-08-2011 at 02:36 PM..
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