[Code Sea Pick-up Shell Perl] find out whether a particular string exists in a string array

Preface

To retrieve whether a string exists in an array, the most basic idea should be to loop through the array and judge the value of each element and the given value to be equal.

(In the Java language you can also convert the array to list, in the list directly with the Contains method can be used)

Look at a simple code:

my @arr2 = qw(str1 str2 str3 str4);
foreach(@arr2)
{
	if($_ eq "str2")
    {
    	print "str2 exist in Array!\n";
    	last;
    }
}

This code looks very concise, and it's not hard to understand. But there is another way to do this in Perl, which requires a single line of code to achieve this effect. is to use the grep function

about grep

The full name of grep is the global Regular expression Print, which translates to an overall regex version.

If you have used a Linux command, you should be familiar with the word.

See a common Linux command

ps -ef | grep java

Ps-ef is to see all the processes

In addition to grep Java, the process of searching for a Java name in a system process.

That is, in Linux, grep can use regular expressions to search for text and print matching lines.

Comprehend by analogy, the grep function works similarly in Perl.

Perl grep function

In Perl, the grep function is called in two ways:

Mode 1. grep BLOCK LIST

Mode 2. grep EXPT, LIST

Block: Represents a code block, usually denoted by {};

EXPR represents an expression, usually a regular expression

List: Lists to match

The grep function matches each element of the list with block or expr, which iterates through the lists and temporarily sets the element to $_.

In the list context, GREP returns all the elements that match the hit, and the result is a list.

In a scalar context, GREP returns the number of elements that match the hit.

Compare the following code:

my @ arr3 = qw (str1 str2 str3 str4 str11);
my $ str = "str1";
my $ result = grep / ^ $ str /, @ arr3;
my @ result2 = grep / ^ $ str /, @ arr3;
print "grep result = $ result \ n"; # returns the number
print "grep [email protected] \ n"; # return element 

This matches the string element starting with str1 in the array.

(Hint in regular expression yes: ^--= start, $ = end)

So to match exactly to a string, use the following method:

My $result =grep/^ $str $/, @arr3;

In this respect, the topic given in the title has been reached.

[Code Sea Pick-up Shell Perl] find out whether a particular string exists in a string array