Shell Programming and Scripting

for file in *.c
do
  cat file.txt "$file" > tempfile
  cat tempfile > "$file"
done
rm tempfile

for file in `find -type f -name *.c |sed 's/\.\///'`
do
sed -i '1{x;s/.*/cat file.txt/ep;x;}' $i
done

# Find all directories inside ., including . itself, and print to stdout line by line
find . -type d | while read DIR # Read each line
do
        for FILE in "${DIR}"/*.c
        do
                # Ignore dirs without c files
                [ -f "$FILE" ] || break

                # Remove the echo, and change '>' to > when you're sure it looks right
                echo cat file.txt "$FILE" '>' "$DIR"/tempfile
                echo cat "$DIR"/tempfile '>' "$FILE"
        done
done

find . -type f -name \*.c -exec sh -c '
    for f; do
        printf "%s\n" "0r file.txt" w q | ed -s "$f"
    done
' sh {} +

find . -type f -name \*.c -exec sh -c 'printf "%s\n" "0r fill.txt" w q | ed -s "$1"' sh {} \;

find . -type f -name "*.c" -exec sh -c 'cat Head.txt "$1" > test.txt && mv test.txt "$1"' sh {} \;

$ find c-files/ -type f -name \*.c | wc -l
   34115


$ time find . -type f -name "*.c" -exec sh -c 'cat fill.txt "$1" > test.txt && mv test.txt "$1"' sh {} \;

real    7m54.556s
user    1m20.358s
sys     5m37.358s


$ time find . -type f -name \*.c -exec sh -c 'printf "%s\n" "0r fill.txt" w q | ed -s "$1"' sh {} \;

real    6m52.460s
user    1m18.580s
sys     5m9.348s


$ time find . -type f -name \*.c -exec sh -c '
> for f; do
> printf "%s\n" "0r fill.txt" w q | ed -s "$f"
> done
> ' sh {} +

real    4m7.945s
user    0m48.030s
sys     3m21.675s