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This article mainly introduces Perl command line what is used, the article is very detailed, has a certain reference value, interested friends must read!

Perl Command Line Applications

This article explains some common Perl command-line arguments that can make your programs more concise and allow you to write a lot of Perl in one line.

Perl has many Perl command-line arguments. It allows you to make your programs simpler and write a lot of Perl with one line. In this article, we'll look at some common Perl command-line arguments.

Safety net parameters have three parameters.

I think they serve as "safety nets" because they allow you to avoid mistakes, especially if you're trying something particularly clever (or stupid) with Perl. Experienced Perl programmers often use these three parameters to find errors in advance.

-C is ***. This parameter compiles the Perl program but does not actually run it. This checks for all syntax errors. Every time I modify a Perl program, I use it immediately to find any syntax errors.

$Perl-cprogram.pl

This ensures that the program can still be compiled. Obviously, it's easier to check immediately after you type a small piece of code than it is to type hundreds of lines of code and start debugging.

-W is the second parameter. It will alert you to any potential bugs. Perl versions after 5.6.0 have replaced-w with usewarnings;. You should use usewarnings because it's more flexible than-w.

-T is the third parameter. It puts Perl in taint mode. In this mode, Perl questions any data that comes in from outside the program. For example, data read from the Perl command line, read from an external file, or transferred from a CGI program. These data are all tainted in the-T mode.

Tainted data cannot be used to interact with external sources.

For example, file names used in system calls and as open. For information on what data is Tainted, see the Perlsec documentation, which has a complete list.

To use Tainted data you must untaint the data. Untaint is implemented through regular expressions, and there is enough to write a separate article about taint itself, so I won't talk too much about taint patterns here. If you are writing a program (such as a CGI program) that needs to accept agnostic input from users, I recommend having taint mode.

Another parameter worth mentioning is-d, which puts Perl in Debugger mode. This topic is very informative and I recommend reading the document 'Perl doc Perl debug' or Richard Foley's Perl Debugger Pocket Reference.

Command-LinePrograms

The following Perl parameters make it easy for short Perl programs to run on the Perl command line: - e allows Perl code to be executed directly by the compiler on the Perl command line. For example, we can run the "HelloWorld" program directly on the Perl command line without calling it a Perl program.

$Perl-e'print"HelloWorld

"'

Multiple-e's can be used simultaneously, depending on where they appear.

$Perl-e'print"Hello";'-e'print"World

"'

Like all Perl programs, only the *** line of the program does not need to end with;. Although you can also refer to modules with-e, -M makes it easier.

$Perl-MLWP::Simple-e'printhead"http://www.example.com"'

-M module name is the same as the use module name. Some modules have default module imports. If you don't want to import them, you can use-m. - m Module name is the same as usemodul (), with default import turned off. For example, in the following example, because the head function is the default import, and-m is not executed, the result is no output.

$Perl-mLWP::Simple-e'printhead"http://www.example.com"'

-m and-M have a lot of convenient syntax to help you use them, and you can list the various arguments to use after =.

$Perl-MCGI=:standard-e'printheader'

Here, CGI.pm's:standard is introduced, and the header function can therefore be used. Multiple arguments can be introduced by using quotes and commas.

$Perl-MCGI='header,start_html'-e'printheader,start_html'

Here we introduce the header and start_html functions. ImplicitLoops-n and-p add looping functionality, allowing you to process files line by line.

$Perl-n-e'somecode'file1

This is the same procedure as below.

LINE: while(){ #yourcodegoeshere }

Note: Open a file on the Perl command line and read it line by line. Each row will be saved by default in $_

$Perl-n-e'print"$.-$_ "'file

The line above can be written LINE:while(){print"$. - $_"} Output the current number of rows $. and the current line $_.

-p can make the above procedure easier.- p outputs the contents of $_, like this:

LINE: while(){ #yourcodegoeshere }continue{ printordie"-pdestination:$! "; }

Continue is here to ensure that print is called on every loop.

◆ Using-p, our print lines program can be changed to $Perl-p-e'$_="$.-$_ "'

In this case, we don't need to explicitly call the print function because it's already called by the-p option.

Note that the LINE: tag allows us to jump directly to the next input record, regardless of how many layers you enter in the loop. Use nextLINE.

$Perl-n-e'nextLINEunless/pattern/;print$_'

Of course, you can also write this:

$Perl-n-e'printunless/pattern/'

In more complex cases, nextLINE can make your code easier to understand.

If you want to do something before and after the loop, you can use BEGIN or ENDblock. The following line of code counts the number of words in the text file.

$Perl-ne'END{print$t}@w=/(w+)/g;$t+=@w'file.txt

All matching words in each row are placed in array @w, and then the number of elements in @w is incremented to $t. Print*** in ENDblock outputs the total number of words in the file.

There are two more parameters that make this program easier. - a Turn on automatic split mode. Space is the default separation sign. The input is separated by a separation number and placed in the default array @F. From this, we can rewrite the above program to

$Perl-ane'END{print$x}$x+=@F'file.txt

You can also change the default separation number to what you want by using-F. For example, make the separation symbol non-character:

$Perl-F'W'-ane'END{print$x}$x+=@F'file.txt

Here's a complex example using the Unixpassword file. Unixpassword is a text file where each line is a user record separated by a colon: . No. Line is the user's login shell path. We can figure out how many users are using each of the different shell paths:

$Perl-F':'-ane'$s{$F[6]}++;'

>-e'END{print"$_:$s{$_}"forkeys%s}'/etc/passwd

Although it is not a single line now, you can see what problems can be solved using parameters. Data separators I mentioned in previous articles $/and $-Input, output separators.$/ Used to separate data read from a file handle. The default $/separator is, so that each time a line is read from the file handle.$ Default is null character, used to automatically add to the end of the data to be printed. This is why print is often added at the end.

$/and $can be used with-n-p. On the Perl command line this corresponds to-0(zero) and-l(this is L). - 0 can be followed by a hexadecimal or octal value, which is assigned to $/. - 00 turns on paragraph mode,-0777 turns on slurp mode (that is, you can read the entire file at once), which has the same effect as setting $/to empty characters and undef.

Using-l alone has two effects.

*** Automatic chomp input separator, the second $/value paid to $(this print will automatically add at the end), individuals often use the-l parameter, used to add to each output. for example

$Perl-le'print"HelloWorld"'

Edit in place We can write very effective Perl command line programs using existing parameters. Common UnixI/O redirects:

$Perl-pe'somecode'output.txt

This program reads data from input.txt, does some processing and outputs it to output.txt. You can also redirect the output to the same file. The above procedure can be made simpler by using the-i parameter. - i Renames the source file and reads from the renamed source file. *** Write the processed data to the source file. If-i is followed by another string, this string is combined with the source filename to produce a new filename. This file is used to store the original file so that it is not overwritten by the-i parameter.

This example replaces all php characters with Perl:

$Perl-i-pe's/PHP/Perl/g'file.txt

The program reads each line of the file, replaces characters, and rewrites (overwrites) the processed data to the source file. If you do not want to overwrite the source file, you can use the

$Perl-i.bak-pe's/PHP/Perl/g'file.txt

The processed data here is written to file.txt, file.txt.bak is a backup of the source file. More information. Perl has a large number of Perl command-line arguments, and this article lists only a few of the most useful.

That's all for "What's the Perl command line for?" Thanks for reading! Hope to share the content to help everyone, more relevant knowledge, welcome to pay attention to the industry information channel!

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