Why does "if [ 0 ]" execute the "then" statement in bash script?

This guide says:

 An if/then construct tests whether the exit status of a list of commands is 0

If I execute 0 in the bash, it says:

0: command not found

So its exit status is not 0, and [ 0 ] should return a non-zero value exit status too. But it returns 0 exit status actually, and if [ 0 ] executes the then statement, not the else statement.
Can anyone explain it?

2

1 Answer

[ isn't part of the if statement, it is a command that evaluates expressions. The [ 0 ] returns true because the form [ Expression ] always evaluates to 0. If you try if [ 1 -eq 2 ] the then statement will not run.

Check the manual page for more info.

1

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