What is the meaning of ~ in linux shell if statement

if is a judgment statement that determines whether something meets a set condition.

1, the format is:

if?condition

then

else

fiDon't forget this ending

2, the three kinds of conditional expressions for if:

if?function?then command execution success, equal to the return of 0? (such as grep?,find a match)? Failure of execution returns non-0? (grep, no match found)

if?[?expression_r_r_r?]?then expression results in true, then returns 0, if directs non-zero values to then

if?test?expression_r_r_r?then expression results in false, then returns non-0 if leads the non-0 value to then