Shell Programming and Scripting

I have to generate the file dynamically from the source file based on the below control file.

Code:

control_file.txt 
1,3,5,-1,8,-1,4

The control file contain the position of column which i required from the source file, Example 1 column ,3 column ,5 column ,blank column(-1 indicates blank column) and so on..

I have written a shell to read one by one position from control file to generate multiple files and finally used paste command to generate new files incase of -1 values i created touch files. Based on sequence of file order its's pasted by ls-v option.

So my existing shell looks like below,

Code:

if [ position != -1 ]
then
cut -d, -f$position > file_$var.csv 
else
touch file_$var.csv
fi
paste -d, $(ls -v file_*.csv) > newe_file.csv

I hope there is a way to minimize the I/O of files, I am looking for something below,

Code:

cut -d, -f1,3,5 > file1.csv
touch file2.csv
cut -d, -f8 > file3.csv
touch file4.csv
cut -d, -f4 > file5.csv

or better solution will be great.

The number of column in source files will be in hundred's

Expected results:

input-file is sample.csv

Code:

col1,col2,col3,col4,col5,col6,col7,col8
1,2,3,4,5,6,7,8
9,10,11,12,13,14,15,16

output.csv

Code:

col1,col3,col5,-1,col8,-1,col4
1,3,5,,8,,4
9,11,13,,16,12

output.csv is based on controlfile.txt

Please suggest me to get some idea , I hope sed can help me to achieve !!

That will be difficult like that because cut will not keep the order of columns. Also you need to somehow put the the columns in file 2 into shell variables first. That wil become a bit cumbersome with a lot of external programs..

An alternative would be to use awk, that for example:

Code:

awk 'NR==FNR{split($0,P); next}{split($0,F); $0=x; for(i in P) $i=F[P[i]]}1' FS=, OFS=, controlfile.txt sample.csv

Note, however, that if you using a UNIX System (rather than a Linux System),awk probably won't work if any lines in your input file are longer than 2048 bytes (actually whatever number is returned by getcont LINE_MAX). With hundreds of input fields, this may be a problem depending on what OS you're using.