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====== BASH - Check if bash is running in interactive mode ======

<code bash>
if [[ $- == *i* ]]
then
  do_interactive_stuff
fi


if [ "$-#*i" == "$-" ]; then
  ...
fi
</code>

<WRAP info>
**NOTE:**  According to **man bash**:

  * PS1 is set and $- includes i if bash is interactive, allowing a shell script or a startup file to test this state.

</WRAP>

----

====== Check if standard input is a TTY ======

<code bash>
if [ -t 0 ] ; then
  echo stdin is a terminal
  .....
fi
</code>

or

<code bash>
if [ -t 1 ] ; then
  echo stdout is a terminal
fi
</code>

<WRAP info>
**NOTE:**   **-t FD** is True if FD is opened on a terminal.

Portable between shells.
</WRAP>

----

===== Examples =====

<code bash>
bash <<< 'test -t 0 && echo Y || echo X
</code>

writes X

<code bash>
bash -c 'test -t 0 && echo Y || echo X
</code>

writes Y

<WRAP info>
**NOTE:**  This also verifies that the standard input is a TTY; although it can be related but it is NOT the same as the shell's interactive mode, which is requested and indicated by shell's "-i" flag.
</WRAP>


----