Splitting a large txt file every 100 lines and including the original header (on a Mac)

Question

I am looking for a tool or script (Textwrangler or Terminal) that can split a larger text file every 100 lines counting from line 5 (the first 4 are header lines) and output individual .txt files which include the original header.

For instance

input:

File.txt
line1 / line4   HEADER
...
line5 / line265 DATA

output:

File_01.txt
line1/line4   HEADER
line5/line104 DATA

File_02.txt
line1/line4   HEADER
line5/line104 DATA

File_03.txt
line1/line4   HEADER
line5/line65  DATA

The text file uses Windows line breaks (CR LF) in case that matters.

I am currently doing this manually so any suggestions that can make this process more efficient are very welcome.

Answer 1

1. Remove the header and put it into a separate file header.txt.
2. split the data using split --lines=100 data.txt (this generate lots of files with 100 lines in them each named xaa xab xac and so on)
3. Then prepend the header to each file for a in x??; do cat header.txt $a > $a.txt; done This results in your finished data files (with headers) being called xaa.txt xab.txt xac.txt ...

If the amount of data is so large (or you split on fewer lines) that xxx files is not enough split makes four letter named files. In that case insert an extra ? in the for-statement above.

Edit:
To automate the extraction of the header use head -4 origdata.txt > header.txt to extract the first four lines. Use tail -n +4 origdata.txt > data.txt to extract everything except the first four lines. Now you have two files one with the header and one with the data. It should not be too hard to combine this to a script. (I have no access to bash today)

Answer 2

Based on the answer provided by Nifle I made a script that executes his suggested commands, adds the original filename to the output and cleans up the temporary files.

#!/bin/bash

FILE=$(ls -1 | grep filename.txt)
NAME=${FILE%%.txt}

head -4 $FILE > header.txt
tail -n +5 $FILE > data.txt

split -l 100 data.txt

for a in x??
    do
        cat header.txt $a > $NAME.$a.txt
    done

mv $FILE $NAME.orig.txt
rm header.txt data.txt x??

Et voila!