Does the Exclamation point represent negation in Bash IF condition?

问题

I've seen something along the lines of

if ! some-command; then
    #do something
fi

What's the effect of the exclamation point? I see that if you use brackets, it can be used for negation.

Is that the same effect here?

回答1:

As documented in man bash:

If the reserved word ! precedes a pipeline, the exit status of that pipeline is the logical negation of the exit status as described above.

回答2:

Correct.

Here is a code sample:

anny ~> if ! grep $USER /etc/passwd
More input> then echo "your user account is not managed locally"; fi
your user account is not managed locally

anny > echo $?
0

anny >

Source: http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html

来源：https://stackoverflow.com/questions/41495350/does-the-exclamation-point-represent-negation-in-bash-if-condition