How to add multiple lines to the beginning of many files in linux?

Question

I have a file beginning.txt that contains lines like:

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How can I execute a linux command to add all the lines in beginning.txt to the top of each file that matches the extension ".customfile" (note that .customfile is just a textfile, but these files may be within subdirectories within my current folder that i also want updated)?

I have many files with the .customfile suffix that I want to append, so looking for a way to do this programatically. I see example with sed command that appear limited to a single line.

sed -i '1s/^/<added text> /' file

Answer 1

With bash:

for file in $(find . -name "*.customfile"); do
  echo Processing $file

  cat beginning.txt $file > $file.modified

  mv $file.modified $file

done

Answer 2

The sed command r is pretty useful in appending contents of a file at certain location, except when that location is line 0.

Inserting your text before line 1 is like appending after line 0. It would've been the solution if sed '0r /path/to/beginning.txt *.customfile was allowed.

You can use process substitution along with sed. The process substitution will generate a sed command that can be run against any files you searched for.

sed -i -f - file < <(sed 's/^/1i/' /path/to/beginning.txt)

The process sed 's/^/1i/' /path/to/beginning.txt will generate sed commands to insert the texts found in /path/to/beginning.txt:

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sed -f - will read the sed command from a file, - means the file is stdin.

If you need to run it on multiple files, you can either use globs or find and xargs.

Sample using multiple files:

sed -i -f - /path/to/*.customfile < <(sed 's/^/1i/' /path/to/beginning.txt)

Sample using find and xargs:

find . -type f -name \*.customfile | xargs -I{} bash -c "sed -f - {} < <(sed 's/^/1i/' /tmp/beginning.txt)"

Alternatively, you can avoid re-running sed 's/^/1i/' /path/to/beginning.txt for every file by assigning the output to a variable and using here string to pass to the sed command.

sedcommand=$(sed 's/^/1i/' /path/to/beginning.txt)
sed -i -f - /path/to/*.customfile <<< "$sedcommand"

Or create a command.sed file from beginning.txt and use it to insert the texts to your custom files.

sed 's/^/1i/' /path/to/beginning.txt > /path/to/command.sed
sed -i -f /path/to/command.sed /path/to/*.customfile