Copying a template header to multiple existing files

I have a bunch of *.csv files that use headers. Right now the files have headers and the same number of lines of data. I need to erase the data in these files, so I figured I could just overwrite the header into the files. I have file A set up properly with the header. How can I cat A into all the other csv files?

Alternatively, how could I delete the last X number of lines from the files? The path for the files is */*.csv

2 Answers

1. Cat the header into each of the files. I am assuming that A is a file since you mentioned cat. If so, you can just copy:

   for file in */*.csv; do cp A "$file"; done

   If A is a variable, do

   for file in */*.csv; do echo "A" > "$file"; done

   Alternatively, if all you need is the first line, you can cat that into each file. That way, it will also work for different headers:

   for file in */*.csv; do head -n "$file" > /tmp/foo && mv /tmp/foo "$file";
   done

2. There are many ways to delete the last X number of lines from the files. Here are three:

   • head, change X to however many lines you want to keep:

     for file in */*.csv; do head -n X $file > /tmp/foo && mv /tmp/foo "$file";
     done

   • awk, change the 123 to however many lines you want to keep:

     for file in */*.csv; do awk 'NR<=123' "$file" > /tmp/foo && mv /tmp/foo "$file";
     done

   • perl, change the 123 to however many lines you want to keep:

     for file in */*.csv; do perl -ne "next if $.>123;print' "$file" > /tmp/foo && mv /tmp/foo "$file";
     done

You can use sed and some pipe creativity to convert a list of files (or anything) into a list of commands.

This is a test, it will just output the commands for you to see what is going to happen:

$ ls *.cvs | sed "s/.*/cat headerfile.cvs > &/"

If you like it, do the same and pipe it to your favorite shell:

$ ls *.cvs | sed "s/.*/cat headerfile.cvs > &/" | bash

Or for a recursive solution you can use find:

find . -name \*.cvs | sed "s/.*/cat headerfile.cvs > &/" | bash