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AWK exclude first and last record, sort and print

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# 1  
Old 11-23-2011
AWK exclude first and last record, sort and print
Hi everyone,
I've really searched for a solution to this and this is what I found so far:

I need to sort a command output (here represented as a "cat file" command) and from the second down to the second-last line based on the second row and then print ALL the output with the specified section sorted. Almost done, BUT:

input:
Code:
~ $ cat test
ID     Done       Have  ETA           Up    Down  Ratio  Status       Name
   1     5%       None  Unknown      0.0     0.0   None  Idle         TEST 1
   2     0%       None  Unknown      0.0     0.0   None  Stopped      TEST 2
   3     9%       None  Unknown      0.0     0.0   None  Idle         TEST 3
   4    40%       10Mb  Unknown      0.0     0.0   None  Stopped      TEST 4
   5    25%       None  Unknown      0.0     0.0   None  Stopped      TEST 5  
Sum          10Mb             0.0     0.0

For the moment I have this:
Code:
~ $ 
~ $ cat test | awk 'NR==1; NR > 1 && NR < '$Num' {print $0 | "sort -k2nr"}'
ID     Done       Have  ETA           Up    Down  Ratio  Status       Name
   4    40%       10Mb  Unknown      0.0     0.0   None  Stopped      TEST 4
   5    25%       None  Unknown      0.0     0.0   None  Stopped      TEST 5  
   3     9%       None  Unknown      0.0     0.0   None  Idle         TEST 3
   1     5%       None  Unknown      0.0     0.0   None  Idle         TEST 1
   2     0%       None  Unknown      0.0     0.0   None  Stopped      TEST 2

Assigning to the Num variable the code cat test | wc -l;

I would like to include the last line to have this:
Code:
ID     Done       Have  ETA           Up    Down  Ratio  Status       Name
   4    40%       10Mb  Unknown      0.0     0.0   None  Stopped      TEST 4
   5    25%       None  Unknown      0.0     0.0   None  Stopped      TEST 5  
   3     9%       None  Unknown      0.0     0.0   None  Idle         TEST 3
   1     5%       None  Unknown      0.0     0.0   None  Idle         TEST 1
   2     0%       None  Unknown      0.0     0.0   None  Stopped      TEST 2
Sum          10Mb             0.0     0.0

But trying
Code:
~ $ cat test | awk 'NR==1; NR > 1 && NR < '$Num' {print $0 | "sort -k2nr"}; END{print}'

I have this, with the last row jumping to the second row: Smilie
Code:
ID     Done       Have  ETA           Up    Down  Ratio  Status       Name
Sum          10Mb             0.0     0.0    
   4    40%       10Mb  Unknown      0.0     0.0   None  Stopped      TEST 4
   5    25%       None  Unknown      0.0     0.0   None  Stopped      TEST 5  
   3     9%       None  Unknown      0.0     0.0   None  Idle         TEST 3
   1     5%       None  Unknown      0.0     0.0   None  Idle         TEST 1
   2     0%       None  Unknown      0.0     0.0   None  Stopped      TEST 2

Also using not a reverse sort with just sort -k2n.

I hope it's clear and not too long.
Thanks in advance!
# 2  
Old 11-23-2011
More detail is always good Smilie

You're seeing the last line come out at top because you're not closing the pipe to the sort command and thus your print is happening before sort finishes and prints it's output. Here's my solution, which also doesn't require knowing the number of records between before hand:

Code:
awk '
    NR == 1 { print; next; }
    {
        if( last )
            print last | "sort -k2nr,2";
        last = $0;
    }

    END {
        close( "sort -k2nr,2" );   # finish sort let sort print
        print last;
    }
' input-file

These 2 Users Gave Thanks to agama For This Post:
dentex vgersh99
# 3  
Old 11-23-2011
Incredibly fast and accurate...
I'm really grateful, thanks mate.
Works like a charm !!!! Smilie

But now I'm FORCED to really understand how it works!!!
Smilie
# 4  
Old 11-23-2011
Quote:
Originally Posted by agama
More detail is always good Smilie

You're seeing the last line come out at top because you're not closing the pipe to the sort command and thus your print is happening before sort finishes and prints it's output. Here's my solution, which also doesn't require knowing the number of records between before hand:

Code:
awk '
    NR == 1 { print; next; }
    {
        if( last )
            print last | "sort -k2nr,2";
        last = $0;
    }

    END {
        close( "sort -k2nr,2" );   # finish sort let sort print
        print last;
    }
' input-file

Hmmm.... I don't quite follow how it works, but it does.
How sorting only one line at a time ends up sorting the whole list (not including the last line?
Care to explain?
Also, some awk-s have the limit on how many file handlers (in this case "sort" invocations) one can have opened - some awk-s have it set to 9. So if your awk has limit set to 9, and you have more than 9 lines in your file, your awk might bomb out....
# 5  
Old 11-23-2011
ok, a somewhat different approach I can understand:
Code:
FNR == 1 { print; next; }
{
  if( last )
    all= (!all)?last:all ORS last
  last = $0
}
END {
  print all | "sort -k2nr,2"
  close( "sort -k2nr,2" )   # finish sort let sort print
  print last
}

# 6  
Old 11-23-2011
Quote:
Originally Posted by vgersh99
Hmmm.... I don't quite follow how it works, but it does.
How sorting only one line at a time ends up sorting the whole list (not including the last line?
Care to explain?
Also, some awk-s have the limit on how many file handlers (in this case "sort" invocations) one can have opened - some awk-s have it set to 9. So if your awk has limit set to 9, and you have more than 9 lines in your file, your awk might bomb out....
It's a bit misleading, but a cool feature of awk....

When the pipe symbol is used awk forks a single process and begins writing to it's stdin or reading from it's stdout depending on where the command and pipe are placed. A more common example is to execute a command and read each record generated:

Code:
function run_it( cmd )
{      while( (cmd|getline)> 0 )   # fork cmd and read from its stdout
        {
           # do something with $0
        }
        close( cmd );
}

As you point out, awk tends to have a limited number of file descriptors available, so it's very important to close them when finished especially in the case of the run_it function that might be called lots of times.

When awk creates the child process, the real FD is mapped using the command string, which is why I tend to put the command into a variable as it's easier to pass it to close, especially if someone comes along and modifies the original command without realising that it needs to be exactly the same in the close.

For the code above, the sort command is forked on the first execution of the statement, and after that awk maps the command string to an already open file descriptor and writes the additional records to the already open FD rather than starting another process. Thus, we get the records we want sorted, and the ones we dont (first and last) are just written to standard output.

This is along the same lines as
Code:
   print foo >"/tmp/file";

Each time the statement is executed the variable contents in foo are printed to the tmp file; the open only happens on the first execution of the statement.

@vgersh99 -- a bit more info than I think you needed, but from the perspective of someone wrestling with the concept of piping a command from inside an awk programme I decided to err on too much.
Last edited by agama; 11-23-2011 at 03:48 PM.. Reason: clarification
This User Gave Thanks to agama For This Post:
vgersh99
# 7  
Old 11-23-2011
Just to add a reference to the relevant part of the manual:


Quote:
print items | command

It is possible to send output to another program through a pipe instead of into a file.
This redirection opens a pipe to command, and writes the values of items through this pipe to another process created to execute command.
The redirection argument command is actually an awk expression. Its value is converted to a string whose contents give the shell command
to be run.

For example, the following produces two files, one unsorted list of BBS names,
and one list sorted in reverse alphabetical order:

Code:
awk '{ 
    print $1 > "names.unsorted" 
    command = "sort -r > names.sorted" 
    print $1 | command 
    }' BBS-list

So, as already stated, it's like:

Code:
zsh-4.3.12[sysadmin]% print -l 3 1 2 | sort
1
2
3

These 2 Users Gave Thanks to radoulov For This Post:
agama vgersh99
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