Concat files in reverse order

Question

I need to concat multiple files to a single file in reverse order.

The order of lines in the files should not be changed.

For example:

file 1.txt
1
2

file 2.txt
3
4

The expected result:

result.txt
3
4
1
2

---

These command do not work as expected:

tac *.txt > result.txt just reverses the order of lines in the files and concat the files in ordinal order. ( 2 1 4 3 )

cat $(ls -r) > result.txt or ls -r | xargs cat > result.txt ls -r | xargs cat > result.txt do not work if filenames have a space character:

cat: file: No such file or directory
cat: 2.txt: No such file or directory
cat: file: No such file or directory
cat: 1.txt: No such file or directory

The problem is that while ls -r returns 'file 2.txt' 'file 1.txt' , but echo $(ls -r) returns file 2.txt file 1.txt that looks like four files for cat .

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Answer 1

Great - so first list the filenames , then reverse their order, then cat them.

find . -type f -name '*.txt' | sort -r | xargs -d'\n' cat

And similar with filename expansion, that is sorted by itself:

printf "%s\n" *.txt | tac | xargs -d'\n' cat

To be fullproff against newlines in filenames, use zero separated streams - printf "%s\0" find.. -print0 xargs -0 tac -s '' .

Remember do not parse ls .

Answer 2

Try this (recursive) function:

function revcat
{
    (( $# == 0 )) && return 0
    revcat "${@:2}"
    cat -- "$1"
}

Example usage:

revcat *.txt

Answer 3

Since there is no short one line command that can be easily be typed from memory. It makes sense to create a function and put it into .bashrc file.

pjh's recursive function works inappropriate slow. So I wrote this one:

function revcat {
  for item in "$@"; do
    echo "$item"; 
  done | tac | xargs -d"\n" cat;
}

It works like cat , but with the expected, reversed, file concatenation order.

For example: revcat *.txt > out.txt .