A simplest Perl program
Here is a basic Perl program we started:
#! / usr / local / bin / perl
#
# Program to do the obvious
#
Print 'Hello World.'; #print a message
We will discuss each of them.
first row:
The first line of each Perl program is:
#! / usr / local / bin / perl
- Although it is different from the system. This trip tells the machine how to do when the file is executed (ie tell it through Perl).
Comments and statements:
Use the # symbol to insert a comment in the program, and is ignored (except the first line) from the # start to this line. The only way to extend the comment to a few lines is to use the # symbol before each row.
The statement in Perl must add a semicolon at the end, like the last line in the above program.
Simple printing:
The PRINT function outputs some information. In the above example it prints out the string hello world, of course, this line is also ended in a semicolon.
You may find that the above program will generate a little unexpected result, then let us run it. Run the program
Use a text editor into this example program and save it. Emacs is a good editor, but you can use any habit of text editor.
Then use the following command to execute.
CHMOD U X ProgName
At UNIX prompt, ProgName is the file name of the program. You can now run this program - run the following command at the prompt:
Perl progname ./progname propname
If there is an error, you will get an error message, or you can't get it. Can use
WARNING parameter running program:
Perl -w propname
This will display warnings and other help information before trying to execute the program. Use the debiller to run the program to use the command:
Perl -d progname
When the program is executed, Perl first compiles and then performs the compiled version. So after the short pause after editing procedure, this program will run very quickly. Scalar
The most basic variable in Perl is scalar. The scalar can be a string or a number, and the string and numbers can be interchangeable. For example, statement
$ priority = 9;
Set the scalar $ priority to 9, but you can also set it as a string:
$ priority = 'high';
Perl also accepts the numbers represented by a string, as follows:
$ priority = '9'; $ default = '0009';
And you can accept arithmetic and other operations.
In general, the variable consists of numbers, letters, and underscores, but cannot start with numbers, and $ _ is a special variable, we will mention it later. At the same time, Perl is sensitive, so $ A and $ A are different variables.
Operators and assignment statements:
Perl uses all C common operators:
$ a = 1 2; # Add 1 and 2 and store in $ a
$ a = 3 - 4; # Subtract 4 from 3 and store in $ a
$ a = 5 * 6; # Multiply 5 and 6
$ a = 7/8; # Divide 7 by 8 to give 0.875
$ a = 9 ** 10; # nine to the power of 10
$ a = 5% 2; # remainder of 5 Divided by 2
$ a; # increment $ a and then return it $ A ; # RETURN $ a and then increment it
$ a; # Decrement $ a and then return it
$ a -; # RETURN $ a and then Decrement IT
For strings, Perl has its own operator:
$ a = $ b. $ c; # Concatenate $ b And $ C
$ a = $ b x $ c; # $ b review $ c times
The assignment statement of Perl includes:
$ a = $ b; # assign $ b to $ a
$ a = $ b; # address $ b to $ a
$ a - = $ b; # Subtract $ b from $ a
$ a. = $ b; # append $ b ontto $ a
Other operators can be found in the Perlop manippage, knock in the man perlop after the prompt.
Interoperability:
The following code prints apples and pears:
$ a = 'apples';
$ b = 'pears';
Print $ a. 'and'. $ b;
In the final print statement, you should only include a string, but:
Print '$ a and $ b';
The result is $ A and $ B, not what we expect.
However, we can use double quotes instead of single quotes:
Print "$ a and $ b";
Double quotation is forced to interoperate any code, and other interoperable code includes special symbols such as wrap (/ n) and analytical (/ t). >> Perl primary tutorial [Day 2]
