Perl - Changing file name in the middle of write - perl

Question

I am trying to take a very large txt file (over a million lines) that I created in Perl and run it through a different statement in Perl that will essentially look something like this (note the following is shell)
a=0
b=1
while read line;
do
echo -n "" > "Write file"${b}
a=($a + 1)
while ( $a <= 5000)
do
echo $line >> "Write file"${b}
a=($a + 1)
done
a=0
b=($b + 1)
done < "read file"
Trying to size it down to 5k lines per file, and incrementing each time (filename1.txt, filename2.txt, filename3.txt, etc)
This doesn't seem to work in shell, possibly due to the size of the input file, and for the life of me I can't think of how to change what file I am writing to in the middle of the loop..

Answer 1

You can just do this in the shell using split.
For example:
split -l 5000 filename.txt filename.txt.
will split filename.txt into multiple files with a max of 5,000 lines each. The output files will be names filename.txt.aa, filename.txt.ab, filename.txt.ac, etc.
From my man split:
NAME
split -- split a file into pieces
SYNOPSIS
split [-a suffix_length] [-b byte_count[k|m]] [-l line_count] [-p pattern] [file [name]]
DESCRIPTION
The split utility reads the given file and breaks it up into files of 1000 lines each. If file is a single dash (`-') or absent, split reads from the stan-
dard input.
The options are as follows:
-a suffix_length
Use suffix_length letters to form the suffix of the file name.
-b byte_count[k|m]
Create smaller files byte_count bytes in length. If ``k'' is appended to the number, the file is split into byte_count kilobyte pieces. If ``m'' is
appended to the number, the file is split into byte_count megabyte pieces.
-l line_count
Create smaller files n lines in length.
-p pattern
The file is split whenever an input line matches pattern, which is interpreted as an extended regular expression. The matching line will be the
first line of the next output file. This option is incompatible with the -b and -l options.
If additional arguments are specified, the first is used as the name of the input file which is to be split. If a second additional argument is specified,
it is used as a prefix for the names of the files into which the file is split. In this case, each file into which the file is split is named by the prefix
followed by a lexically ordered suffix using suffix_length characters in the range ``a-z''. If -a is not specified, two letters are used as the suffix.
If the name argument is not specified, the file is split into lexically ordered files named with the prefix ``x'' and with suffixes as above.

Answer 2

As an aside, this is your fixed script:
#!/bin/sh
a=0
b=1
while read line; do
if [ $a -eq 0 ]; then
echo -n '' > out-file-${b}
fi
echo $line >> out-file-${b}
a=$(( $a + 1 ))
if [ $a -eq 10 ]; then
a=0
b=$(( $b + 1 ))
fi
done < in-file
Tested with bash and dash.