Why piping to the same file doesn't work on some platforms?

Question

In cygwin, the following code works fine

$ cat junk
bat
bat
bat

$ cat junk | sort -k1,1 |tr \'b\' \'z\' > junk

$ cat junk
zat
zat
zat

Answer 1

Using the following simple script, you can make it work like you want to:

$ cat junk | sort -k1,1 |tr 'b' 'z' | overwrite_file.sh junk

overwrite_file.sh

#!/usr/bin/env bash

OUT=$(cat -)

FILENAME="$*"

echo "$OUT" | tee "$FILENAME"

Note that if you don't want the updated file to be send to stdout, you can use this approach instead

overwrite_file_no_output.sh

#!/usr/bin/env bash

OUT=$(cat -)

FILENAME="$*"

echo "$OUT" > "$FILENAME"