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Split File Based on Line Number Pattern

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Top Forums Shell Programming and Scripting Split File Based on Line Number Pattern
# 8  
Old 09-30-2008
Hammer & Screwdriver For this instance, I too think era had the better solution
I started working on my approach, and thought of trying as era did. I wanted to finish my approach, thinking the grabbing of line # from the cat -n command, and using it to determine a next step might prove an interesting exercise.
Also, era's solution would probably run a lot faster than mine!
# 9  
Old 09-30-2008
With AWK (if I'm not missing something):

[use nawk or /usr/xpg4/bin/awk on Solaris]
Code:
awk '!(NR%10){print>(FILENAME 4);next} 
{print>(FILENAME (++c%4?++i:i?i:++i))}
i==3{i=c=0}' filename

For best performance use mawk if available:

Code:
% repeat 1000000 print ${(l:100::x:)l=line}$((++i)) >> data

% wc data
  1000000   1000000 106888896 data

% time gawk '!(NR%10){print>(FILENAME 4);next}
{print>(FILENAME (++c%4?++i:i?i:++i))}
i==3{i=c=0}' data

gawk  data  3.28s user 0.37s system 97% cpu 3.756 total

% time mawk '!(NR%10){print>(FILENAME 4);next}
{print>(FILENAME (++c%4?++i:i?i:++i))}
i==3{i=c=0}' data

mawk  data  1.44s user 0.42s system 95% cpu 1.939 total

% time nawk '!(NR%10){print>(FILENAME 4);next}
{print>(FILENAME (++c%4?++i:i?i:++i))}
i==3{i=c=0}' data

nawk  data  8.07s user 3.61s system 93% cpu 12.516 total

Last edited by radoulov; 09-30-2008 at 04:31 PM..
# 10  
Old 10-01-2008
Actually, this is sufficient Smilie

Code:
awk '!(NR%10){print>(FILENAME 4);next}
{print>(FILENAME (++i))}i==3{i=0}' filename

# 11  
Old 10-01-2008
Just for completeness, I should note that the modulo arithmetic in the Perl script I posted was a major brain fart. Here's a hopefully corrected version, with an explanation.

Code:
perl -MIO::File -ne 'BEGIN {
  @n = ("one.txt", "two.txt", "three.txt", "four.txt");
  map { $file[$_] = IO::File->new(">$n[$_]") || die $!} 0..3; 
  @m = (3, 0, 1, 2, 0, 1, 2, 0, 1, 2);
}
$file[$m[$. % 10]]->print || die $!' filename

I threw in the mapping of arbitrary file names in the array @n for show.

The BEGIN block creates an array @file of four file handles (indexed 0 through 3 -- Perl arrays start at zero) and a mapping @m of which line number to print to which handle. Somewhat confusingly, the first entry in the mapping is for line numbers 10, 20, 30, ... (array index zero), while only the second is for line numbers 1, 11, 21, etc.

In the main loop (outside the BEGIN block) we simply calculate the remainder (modulo) of the line number $. divided by 10 (not 9!!) and use that as an index into @m to get the handle index, and then through another level of indexing print to the handle we are pointed to.

Also for the record, the shell version will have an issue if there is input with backslashes in it. Change read to read -r or if your shell doesn't support that, see if you have the line command instead. Also for maintainability I suppose it would be better to use higher-numbered file descriptors -- file descriptors 1 and 2 are reserved for standard output and standard error, as you probably know. (I wanted to keep them in sync to make the script easier to follow, but it sucks if you try to debug it and lose all your errors into a file someplace.)

As usual, Radoulov's solution is impressive, though a bit hard to follow. Apparently the names of the output files will be the input file name with a number suffix added.

I speculate that mawk keeps the file handles open just in case, i.e. secretly does the file handle juggling that I did explicitly in the Perl script. (Incidentally, you don't really need IO::File for that, but it makes it a lot more readable -- the stuff you have to do to manipulate bare file handles in bare Perl is arcane even by Perl standards.)
Last edited by era; 10-01-2008 at 04:04 AM.. Reason: Note on file descriptor numbering in sh implementation
# 12  
Old 10-01-2008
Thanks era!

As far as I know [ngm]awk should maintain the files open until the end of the program or an explicit close call (close(filename)):

Code:
% strace  -eopen mawk '!(NR%10){print>(FILENAME 4);next}
{print>(FILENAME (++i))}i==3{i=0}' data
open("tls/i686/sse2/cmov/libm.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
[snip]
open("/lib/tls/i686/cmov/libc.so.6", O_RDONLY) = 3
open("data", O_RDONLY)                  = 3
open("data1", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 4
open("data2", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 5
open("data3", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 6
open("data4", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 7
Process 8618 detached

Code:
% strace  -eopen gawk '!(NR%10){print>(FILENAME 4);next}
{print>(FILENAME (++i))}i==3{i=0}' data
open("tls/i686/sse2/cmov/libdl.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
[snip]
open("/usr/lib/locale/en_US.utf8/LC_TIME", O_RDONLY) = 3
open("data", O_RDONLY|O_LARGEFILE)      = 3
open("data1", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 4
open("data2", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 5
open("data3", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 6
open("data4", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 7
Process 8641 detached

Reading the strace output I notice some differences in read/write calls timings.
I'm quite sure that the below output does not show all time consuming events.

Code:
% strace -c mawk '!(NR%10){print>(FILENAME 4);next}
{print>(FILENAME (++i))}i==3{i=0}' data
Process 7865 detached
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 73.48    0.003954           0     26097           write
 25.83    0.001390           0     26313           read
  0.69    0.000037           1        57        49 open
  0.00    0.000000           0        10           close
  0.00    0.000000           0         1           execve
  0.00    0.000000           0         1           time
  0.00    0.000000           0         4         4 access
  0.00    0.000000           0         3           brk
  0.00    0.000000           0         5         5 ioctl
  0.00    0.000000           0         5           munmap
  0.00    0.000000           0         3           mprotect
  0.00    0.000000           0        13           mmap2
  0.00    0.000000           0        16        15 stat64
  0.00    0.000000           0         7           fstat64
  0.00    0.000000           0         1           set_thread_area
------ ----------- ----------- --------- --------- ----------------
100.00    0.005381                 52536        73 total

% rm data[1-4]                                     
% sync;sync                                        
% strace -c gawk '!(NR%10){print>(FILENAME 4);next}
{print>(FILENAME (++i))}i==3{i=0}' data
Process 7883 detached
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 72.16    0.004391           0     26097           write
 27.21    0.001656           0     26102           read
  0.62    0.000038           0        89        72 open
  0.00    0.000000           0        17           close
  0.00    0.000000           0         1           execve
  0.00    0.000000           0         5         5 access
  0.00    0.000000           0         3           brk
  0.00    0.000000           0         6         5 ioctl
  0.00    0.000000           0         6           munmap
  0.00    0.000000           0         4           mprotect
  0.00    0.000000           0         4           _llseek
  0.00    0.000000           0         3           rt_sigaction
  0.00    0.000000           0        22           mmap2
  0.00    0.000000           0        16        15 stat64
  0.00    0.000000           0        25           fstat64
  0.00    0.000000           0         2           getgroups32
  0.00    0.000000           0        13           fcntl64
  0.00    0.000000           0         1           set_thread_area
------ ----------- ----------- --------- --------- ----------------
100.00    0.006085                 52416        97 total

% rm data[1-4]                                     
% sync;sync                                        
% strace -c newawk '!(NR%10){print>(FILENAME 4);next}
{print>(FILENAME (++i))}i==3{i=0}' data
Process 7943 detached
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 98.90    0.123052           0   1000000           write
  1.10    0.001368           0     26101           read
  0.00    0.000000           0        64        52 open
  0.00    0.000000           0        15           close
  0.00    0.000000           0         1           execve
  0.00    0.000000           0         4         4 access
  0.00    0.000000           0         3           brk
  0.00    0.000000           0         7           munmap
  0.00    0.000000           0         3           mprotect
  0.00    0.000000           0         1           rt_sigaction
  0.00    0.000000           0        18           mmap2
  0.00    0.000000           0        16        15 stat64
  0.00    0.000000           0        12           fstat64
  0.00    0.000000           0         1           set_thread_area
------ ----------- ----------- --------- --------- ----------------
100.00    0.124420               1026246        71 total
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