Question

#! /bin/bash

if [ !\(-f new.bash -o -d new.bash\) ]
then
    echo "Neither"
else
    echo "yes"
fi

it works but leaves an error:

/file_exist_or_not.bash      
./file_exist_or_not.bash: line 3: [: too many arguments
yes

BTW, Why the inner parenthesises needs to be escaped?

Answer 1

Bash uses spaces to separate tokens, which are then passed as arguments to the commands (in this case the command is test). See the man page for test for more details.

To solve, you need to add spaces between the operands.

if [ ! \( -f new.bash -o -d new.bash \) ]