Shulou(Shulou.com)06/02 Report--

Xiaobian to share with you what Perl basic knowledge points, I believe most people do not know how, so share this article for everyone's reference, I hope you have a lot of gains after reading this article, let's go to understand it together!

Perl basics

（1）helloworld.pl

usestrict;//turn on strict syntax and variable checking

usewarnings;//turn on additional compile and runtime warnings

print"helloworld\n";//Print information

Run mode, command line: perlhelloworld.pl

(2) Perl Basic Variables and Simple Expressions

There's only one variable, a string.

Definition of variables:

my$size=42;#This is a comment

My stands for local variable, 42 is actually "42"

If the variable is not initialized, it is assigned a special value undef, and comparing, printing, or performing arithmetic operations on undef will cause errors.

(3) Perl base print variables:

print"size=$size"

print size=42;

If you want to print "$," escape is required

perl also has printf, similar to c, but only used where precise control of variable format is required, such as: printf"%3d:%-20s%5.2f\n",$sequence,$description,$amount;

(4) Perl basic operators

As with C, there are:

.：string concatenation

**: Power

x: Repeat, for example: my$no="no"x3;

(5) Reference rules for Perl basics

If there are characters after the output string, they need to be separated by braces, for example:

my$title="$name\t${size}inches"

If you don't want Perl to tamper with your string, use single quotes. Perl doesn't interpret anything in single quotes unless\'and\\

(6) Perl fundamental numerical constants

Same as c, including octal and hexadecimal, underscore is also allowed in numbers, for example:

my$cost=1_333_832;

(7) Perl basic read input

Read inputs from standard inputs:

$variable=;(stdin can also be all lowercase)

The entire line will be read up to the new line, including your carriage return.

chomp($name), which removes the new line at the end of the string

(8) If statements and relational operators

For example:

if($size==1){

}elsif($size==2){//Note not elseif

}else{

die("Error");//Print error message and exit

}

Relational operators are used for numbers and strings, respectively:

numeric string

==eq

!= ne

=ge

If the string is operated on by a numeric relationship, the string is converted to 0 and a warning is displayed

(9) Whether the test variable has a value

defined($value)

Def ($value)

(10) True definition

false: undefined variable, empty string, value "0"

true: Other circumstances

(11) Perl Basic Loop Statements

while(condition){

last;//exit loop, similar to break in c

}

for($i=0;$i

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