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To split large files into smaller files in Unix, use the split  command. At the Unix prompt, enter:

split [options] filename prefix 

Replace filename with the name of the large file you wish to split. Replace prefix with the name you wish to give the small output files. You can exclude [options ], or replace it with either of the following:

The split  command will give each output file it creates the name prefix  with an extension tacked to the end that indicates its order. By default, the split  command adds aa  to the first output file, proceeding through the alphabet to zz  for subsequent files. If you do not specify a prefix, most systems use  x .

Examples

For more information, consult the man page for the split  command. At the Unix prompt, enter:

man split

csplit  command

There is also csplit  command, which splits files based on context. For more information, see the man page for the csplit  command. At the Unix prompt, enter:

man csplit

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[Nov 08, 2017] Skipping null/empty fields caught by split()

Jun 01, 2019 | bytes.com

sicarie

I am attempting to parse a CSV, but am not allowed to install the CSV parsing module because of "security reasons" (what a joke), so I'm attempting to use 'split' to break up a comma-delimited file.

My issue is that as soon as an "empty" field comes up (two commas in a row), split seems to think the line is done and goes to the next one.

Everything I've read online says that split will return a null field, but I don't know how to get it to go to the next element and not just skip to the next line.

Expand|Select|Wrap|Line Numbers

  1. while (<INFILE>) {
  2. # use 'split' to avoid module-dependent functionality
  3. # split line on commas, OS info in [3] (4th group, but
  4. # counting starts first element at 0)
  5. # line = <textonly>,<text+num>,<ip>,<whatIwant>,
  6. chomp($_);
  7. @a_splitLine = split (/,/, $_);
  8. # move OS info out of string to avoid accidentally
  9. # parsing over stuff
  10. $s_info = $a_splitLine[3];
Could anyone see either a better way to accomplish what I'm trying to do, or help get split to capture all the elements?

I was thinking I could run a simple substitution before parsing of a known string (something ridiculous that'll never show up in my data - like &^%$#), then split, and then when printing, if that matches the current item, just print some sort of whitespace, but that doesn't sound like the best method to me - like I'm overcomplicating it.

Jun 19 '09 # 1



Expert Mod 100+

P: 465
RonB
My issue is that as soon as an "empty" field comes up (two commas in a row), split seems to think the line is done and goes to the next one .
No it doesn't. You have a flawed impression of what's happening.

Expand|Select|Wrap|Line Numbers

  1. C:\TEMP>type test.pl
  2. #!/usr/bin/perl
  3. use strict;
  4. use warnings;
  5. use Data::Dumper;
  6. my $str = 'a,,,b,,,,6,,';
  7. my @fields = split /,/, $str;
  8. print Dumper @fields;
Expand|Select|Wrap|Line Numbers
  1. C:\TEMP>test.pl
  2. $VAR1 = 'a';
  3. $VAR2 = '';
  4. $VAR3 = '';
  5. $VAR4 = 'b';
  6. $VAR5 = '';
  7. $VAR6 = '';
  8. $VAR7 = '';
  9. $VAR8 = '6';
Expand|Select|Wrap|Line Numbers
  1. C:\TEMP>perldoc -f split
  2. split /PATTERN/,EXPR,LIMIT
  3. split /PATTERN/,EXPR
  4. split /PATTERN/
  5. split Splits the string EXPR into a list of strings and returns that
  6. list. By default, empty leading fields are preserved, and empty
  7. trailing ones are deleted. (If all fields are empty, they are
  8. considered to be trailing.)
  9. ....
  10. ....
  11. ....
Jun 19 '09 # 2

reply


Expert Mod 2.5K+

P: 4,667
sicarie

Interesting, so then how would I access the b or the 6?

  1. #!/bin/perl
  2. use strict;
  3. use warnings;
  4. use Data::Dumper;
  5. my $str = 'a,,,b,,,,6,,';
  6. my @fields = split /,/, $str;
  7. my $n = 0;
  8. print Dumper @fields;
  9. while ($fields[$n]) {
  10. print "$n: $fields[$n]\n";
  11. $n++;
  12. }
  13. print "done!\n";
Expand|Select|Wrap|Line Numbers
  1. $ ./splitTest.pl
  2. $VAR1 = 'a';
  3. $VAR2 = '';
  4. $VAR3 = '';
  5. $VAR4 = 'b';
  6. $VAR5 = '';
  7. $VAR6 = '';
  8. $VAR7 = '';
  9. $VAR8 = '6';
  10. 0: a
  11. done!
In the above, my attempt to print with a while loop stops as soon as the first empty set is reached. I'm guessing I'd have to check each one to see which are valid and which are not, but what am I looking for - null?

Jun 19 '09 # 3

reply

Expert Mod 100+

P: 465
RonB

If you know which field/index you want, then simply print that field.

If you want/need to loop over the array elements, then use a for or foreach loop, not a while loop.

Expand|Select|Wrap|Line Numbers
  1. for my $i ( 0..$#fields ) {
  2. # only print fields that have a value
  3. print "induce $i = '$fields[$i]'\n" if length $fields[$i];
  4. }
Jun 19 '09 # 4

reply


Expert Mod 2.5K+

P: 3,496
numberwhun

I have to agree with Ron. Since this is a csv file, you should already know which field is what. All you would have to do is reference it by its index. Otherwise, you can use the code above to iterate through each one and pull out the variables with values other than null.

Regards,

Jeff

Jun 20 '09 # 5

reply


Expert Mod 2.5K+

P: 4,667
sicarie

Cool, thanks. I am really only interested in one of those fields, but then have to make sure once I edit that field, I re-append all the others back on, so I will play around with that.

Thanks again!

[Nov 23, 2009] Merging Split Files

October 11th, 2007

Jesus asks: I have a question about the split Command… How can I "come back" to "largefile" from 126 small files?It sounds like the split command was used? If so, then you can use a for loop with file concatenation. First, I will split the files for my example:

$ ls -l big.log
-rw-rw-r--  1 brock brock 175743061 Oct 11 22:08 big.log
$ expr 175743061 \/ 126
1394786
$ split -b 1394786 big.log
$ ls -1 x*
xaa
xab
...
xew

Split creates its output files in decreasing alphabetic order. Thus when you list them in the shell they are in the order in which
they were split. As such, you can simply use cat to merge the files. (Thanks to Paul and Davidov for pointing out my for loop was superfluous.)

$ cat x* >merged.big.log
$ ls -l *.log
-rw-rw-r--  1 brock brock 175743061 Oct 12 22:08 big.log
-rw-rw-r--  1 brock brock 175743061 Oct 12 01:11 merged.big.log
$ diff merged.big.log big.log
$ md5sum *.log
47de08911534957c1768968743468307  big.log
47de08911534957c1768968743468307  merged.big.log



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