Make interactive execute whenever possible

Here the trick is to restore those file descriptors (0, 1, 2) that have been
redirected (`dup2`) by the parent process.

First we need to determine which one has been redirected, for example by looking
at `ls -l /proc/$$/fd/`. Then we can use `0<&x`, `1>&x` or `2>&x` to restore 0,
1 or 2 respectively, where `x` is any file descriptor number that points to the
TTY.

It may happen that no file descriptor is unchanged, in that case we can use
`tty` to perform the redirection: sh <$(tty) >$(tty) 2>$(tty)

_gtfobins/xargs.md

@@ -3,6 +3,11 @@ functions:
   execute-interactive:
     - description: GNU version only.
       code: xargs -a /dev/null sh
+    - code: echo x | xargs -Iy sh -c 'exec sh 0<&1'
+    - description: Read interactively from `stdin`.
+      code: |
+        xargs -Ix sh -c 'exec sh 0<&1'
+        x^D^D
   file-read:
     - description: This works as long as the file does not contain the NUL character, also a trailing `$'\n'` is added. The actual `/bin/echo` command is executed. GNU version only.
       code: |