How can I add a string to the beginning of each file in a folder in bash?

Question

I want to be able to prepend a string to the beginning of each text file in a folder. How can I do this using bash on Linux?

Answer 1

This will do that. You could make it more efficient if you are doing the same text to each file...

for f in *; do 
  echo "whatever" > tmpfile
  cat $f >> tmpfile
  mv tmpfile $f
done

Answer 2

You may use the ed command to do without temporary files if you like:

for file in *; do
  (test ! -f "${file}" || test ! -w "${file}") && continue                # sort out non-files and non-writable files
  if test -s "${file}" && ! grep -Iqs '.*' "${file}"; then continue; fi   # sort out binary files
  printf '\n%s\n\n' "FILE:  ${file}"
  # cf. http://wiki.bash-hackers.org/howto/edit-ed
  printf '%s\n' H 0a "foobar" . ',p' q | ed -s "${file}"  # dry run (just prints to stdout)
  #printf '%s\n' H 0a "foobar" . wq | ed -s "${file}"     # in-place file edit without any backup
done | less

Answer 3

You can do it like this without a loop and cat

sed -i '1i whatever' *

if you want to back up your files, use -i.bak

Or using awk

awk 'FNR==1{$0="whatever\n"$0;}{print $0>FILENAME}' *