除非unless语句后可以跟可选的 elsif ... else 语句,这对于使用单个unless... elsif语句测试各种条件非常有用。
Perl编程语言中的unless...elsif ... else 语句的语法是-
unless(boolean_expression 1) { # Executes when the boolean expression 1 is false } elsif( boolean_expression 2) { # Executes when the boolean expression 2 is true } elsif( boolean_expression 3) { # Executes when the boolean expression 3 is true } else { # Executes when the none of the above condition is met }
#!/usr/local/bin/perl $a=20; # check the boolean condition using if statement unless( $a == 30 ) { # if condition is false then print the following printf "a has a value which is not 20\n"; } elsif( $a == 30 ) { # if condition is true then print the following printf "a has a value which is 30\n"; } else { # if none of the above conditions is met printf "a has a value which is $a\n"; }
在这里,我们使用等于运算符==,用于检查两个操作数是否相等。如果两个操作数相同,则返回true,否则重新运行为false。
a has a value which is not 20
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