Split Large File – How to Split a Large File on Windows

This is not the simplest answer, hopefully someone will come up with something neater. I put together a little script which will do this that should work on the Mac.

#!/bin/bash
NUMFILES=`grep '^--.*--' $1 | wc -l`
NUMFILES=$(($NUMFILES - 2))
csplit -k $1 '%^--.*--$%' '/^--.*--$/' "{$NUMFILES}" 
for file in `ls xx*`
do
        mv $file "`head -n1 $file | sed -e 's/--\(.*\)--/\1.txt/'`"
done

This works using csplit to chop up the file. The fourth line basically says ignore everything before the first header line and then split up the headers after that. lines 2-3 work out how many times csplit has to split up the file.

csplit names its output files xx followed by a 2 digit number. The last 4 lines rename all these files to whatever is in the header line with the -- removed.

You can just use "grep" with the -A and/or -B options. The -A switch will read the X number of lines after the error, so it's probably what you want, and the -B switch will read X number of lines before the error, so you would do something like this:

grep -A10 -B2 "string to find" /path/and/file.tofind

to find the 10 lines which occur after "string to find", as well as the 2 lines before it.

Alternatively – and it's probably a much worse solution, you could simply use "head" and "tail" to find the first and then the last part of the file you want; but this assumes you know the line numbers. I.e., if you have a long line file, and you are wanting to read lines 500-510, you might try this:

head -510 /etc/file/to/search | tail -10

Which would first extract the first 510 lines of the file, and then read off the last 10 of those lines.