Perl: Control Structure

Perl Structure Control Statements:

If condition statement:

if (condition) {

Expression

} elsif {

Expression

} else {

Expression

}

Unless conditional statements:

The condition is false when executed.

Unless (condition) {

Expression

} elsif {

Expression

} else {

Expression

}

While Loop statement:

while (condition) {

Expression

}

while (1) {

...

} #死循环

Until Loop statement:

Execute only when the condition is false

Until (condition) {

Expression

}

foreach Loop statement:

foreach $var (@arry/list) {

Expression

}

$var loop variable is not a copy of the list element, but the list element itself.

If you modify the loop variable in the foreach body, you modify the elements in the list.

$var loop variable restores the original value after exiting the Foreach loop.

The loop variable can be omitted, and the default is to use $_ instead:

foreach (@arry/list) {

print "$_";

}

For Loop statement:

The For and foreach equivalents in Perl can be converted to each other according to the conditions.

for (initialization; condition; increment) {

Expression

}

for (;;) {

...

} #死循环

Bare BLOCK:

{

Expression

}

Last function : Jumps out of the loop, equivalent to the break of C.

Last label/expr

next function : Jump out of this cycle, continue the next cycle, the equivalent of C continue.

Next label/expr

redo function : Unconditionally jump to the top of this cycle, re-execute this cycle.

Redo Label/expr

Given-when Control Structure:

Given ($var) {

When (condition) {expression}

...

default {expression}

}

When matching for multiple projects:

foreach (@arr) {

When (condition) {expression; continue}

...

default {expression}

}

break: Jump out of given block

continue: continue with the next sentence

Conditional modifiers:

dosomething if condition;

Can also be written as:

DoSomething

if condition;

tags in the loop:

A jump can be achieved by adding a tag to the Loop keyword such as for/while.

The label is capitalized, and can be alphanumeric and glide, but not a number.

Eval Expr/block: Capturing errors

special variables [email protected] Store the error message if no exception is triggered [email protected] is empty.

eval {

....

}

if ([email protected]_) {

Print "An error occurred ([email protected]), continuing\n";

}

Evalbytes

Goto

Return

Exit

Do

Wantarray

Dump

Caller

"__file", "__line__", "__package__", "__sub__"

Perl: Control structure