The "opposite" of &> /dev/null
bash, dev-null, if-statement
Solution
Your `&> /dev/null` redirects the stdout and stderr output to `/dev/null`, effectively suppressing all output of the process. The exit code of the program (the numerical "result", typically stating "success" (0) or "failure" (any other number)) is not influenced by that.
To reverse the condition (the `diff`), just insert an exclamation mark, stating a `not` operator:
if ! diff "/home/folder1/" "/home/folder2/" &> /dev/null ; then
...
The `diff` tool always terminates with exit value `0` if (and only if) it does not find any difference. If there is a difference, `1` is the exit value; if there is trouble (I/O error or such things), `2` is the exit value. The `if` of the shell interprets exit values of `0` to be true and all other values to be false (mind that, because this is quite the opposite of other programming languages!).
Problem
I use the following script to compare to folders: ``` if diff "/home/folder1/" "/home/folder2/" &> /dev/null ; then echo "Files in the two folders are the same" else echo "Files in the two folders are NOT the same" fi ``` Is there a brief way of explaining what the "&> /dev/null" actually does, does it return a boolean value of true/false? And my main question: What would the opposite be? I mean, say I want the "if diff" question to be "Is the content of the two folders NOT the same?"