Perl Grammar Quick Check

While learning Perl, Python, and shell scripts can easily confuse their syntax, this article is primarily a personal summary that facilitates the use of queries.

Perl basic syntax, installation, help documentation

File Header format:

 
 
#!/usr/bin/perl
use strict;
use warnings;

Run the Perl script:

#call perl program
Perl test.pl
#Executable script
Chmod 755 test.pl
./test.pl 

Basic reading and writing:

#keyboard input
$a = <STDIN>;
Chomp($a);
Print $a;

#File input
Open(IN, "<test.txt") or die "Cannot open file:$!\n";
Open(OUT, ">test.txt") or die "Cannot open file:$!\n";
While(<IN>){
     Chomp;
     Print OUT "1. $_";
     Last;
};
Close(IN);
Close(OUT); 

Basic Control Flow:

If( ){

}elsif( ){

}else{

}
Print "Hello!" if (1 == 1); #shorthand
While( ){
     $count++;
}

For($i; $i <= 10; $i++){

}

Foreach (@array){
     Print $_;
}
Last; #break
Next; #continue

Data structure: Scalar quantity ($), list (), array (@), hash (%), file handle (<>)

Syntax structure: The statement ends with a semicolon (;), the code block is delimited with curly braces {}, and the dynamic language does not have to indicate the variable type

Single double quotes: single quote q (), all output as-is, double quotation mark QQ (), allow inserting variable

Syntax Conventions: There are many places in Perl where parentheses () are available, especially built-in functions such as print, split, and so on; You can use the increment decrement operator

Install: Windows installed active version, (perl-v) check, Linux pack,

$ tar -zxvf stable.tar.gz -C dir
$ sh Configure # Configure
$ make # installation
$ make test #test whether make succeeds
$ make install 

Help document: Perldoc command

Perldoc # will prompt usage
Perldoc perl # will show detailed usage
Perldoc perlfunc #Three modules
Perldoc perlop
Perldoc perlfaq

It is recommended to use a browser to view local HTML documents:

file:///D:/Program%20Files/Perl64/html/index. html

Keywords: special variables

$_: The default parameter, which is the current default action parameter, is important in reading files <FILE>, iterating for (@array), split//, Print

$!: standard error output, usually only with or Die statement

$: A variable within the first parenthesis in the regular expression pattern, such as (. *), (string), and so on

An array of arguments passed by the @_:sub function,

Keyword: string operator

Connection string: The collocated operator (.)

Escaped: backslash \

Distinguish between scalar and string: {} Displays the specified variable name, such as ${name}space

repeating operator (x), such as "-" x 10

Keyword: array, hash

List: Lists are constants, created by parentheses (), separated by commas

# Range operator
@a = (1..10)
@b = (1..10, 21..30)
@list=(aa..zz); 

Create an array: Create an array with a list ()

Referencing arrays: Referencing arrays with square brackets [] subscript

Create hash: Creates a hash with a list (), in order to look good, the key value pairs are organized in the form of = =, or you can create individual

Reference hash: Reference hash with curly braces {}

Keyword: array manipulation

Keywords: (numeric/String) comparison

Numeric comparisons: (= =, >, <, >=, <=,! =)

String comparisons: (eq, GT, lt, ge, le, ne)

Keywords: print usage

Print: Can be directly connected to the variable $var, @array,%hash, the output is no space carriage return, all elements are linked together, an array of a lump, hash a lump, where the hash order is chaotic.

Print: can be double quotation marks, there are spaces between the array, can be distinguished, the hash is invalid, no content, it shows the%hash.

Print: When output to a file, the file handle is in front, the middle is a space (not a comma), followed by the output

Keywords: q (), QQ (), QW (), qx{}

Q (): Enclose the content in single quotation marks

QQ (): Enclose the content in double quotation marks

QW (): A sequence of spaces separated by single quotation marks to assemble an array, shielding the scalar inside

# Both are equivalent, it is best not to have embedded variables
@a = qw(abc def ghi)
@b = (‘abc‘,‘def‘, ‘ghi‘) 

qx{}: Capture command output

$directory = `dir`; 
$directory_2 = qx{dir};

Keywords: regular expressions, patterns

Keywords: functions

Standard function Format:

Keywords: common built-in functions

int (5.20);

Length ("Nose");

LC ("ME TOO");

UC ("HAL 9000");

COS (50);

RAND (5)

Keyword: stack operation function

Push ()

Pop ()

Shift (): Remove the last element, common language handler function parameters

Unshift ()

Keywords: command line

Keyword: context

Keyword: chomp

Chomp is an operator that can use parentheses or spaces; it changes the parameter variable, and its return value is 1 or 0

$a = "lizhiixn\n";
Print $a;
Print "next\n";
Chomp $a;
Print $a;
Print "next";
$b = chomp($a); #very rarely used 

Perl Grammar Quick Check