Bash find or xargs evaluates variables and subshells only once

I noticed that find ... -exec ... {} \; or xargs -i ... {} seems to evaluate variables or subshells (like $RANDOM or $(uuidgen)) only once, even the command was executed mutiple times.

For example:

$ find . -type f -name \*.txt -exec echo "$RANDOM {}" \;
28855 ./foo/bar.txt
28855 ./foo/bar1.txt
28855 ./foo/bar2.txt
28855 ./foo/bar3.txt
28855 ./foo/bar4.txt

$ grep -lr SOME_TEXT --include=\*.txt | xargs -i echo "$RANDOM {}"
6153 ./foo/bar.txt
6153 ./foo/bar1.txt
6153 ./foo/bar2.txt
6153 ./foo/bar3.txt
6153 ./foo/bar4.txt

Is there a way to get a result like below?

1543 ./foo/bar.txt
543 ./foo/bar1.txt
57224 ./foo/bar2.txt
3525 ./foo/bar3.txt
18952 ./foo/bar4.txt

>Solution :

Yes. The variable expansion is performed after the line has been accepted, but before it has been executed. This means that the command that ends up being executed is

'/usr/bin/find' '.' '-type' 'f' '-name' '*.txt' '-exec' 'echo' '28855 {}' ';'

Two basic ways around this:

• Use another bash that will delay the execution:

  find . -type f -name \*.txt -exec bash -c 'echo "$RANDOM {}"' \;
  

• Use a loop:

  for file in $(find . -type f -name \*.txt -print)
  do
    echo "$RANDOM $file"
  done
  

• If your files have spaces, you have to do something different to preserve them:

  mapfile -d '' files < <(find . -type f -name \*.txt -print0)
  for file in "${files[@]}"
  do
    echo "$RANDOM $file"
  done