perl 裏面如何寫出閱讀友好的代碼提示

在咱們使用別人寫好的程序時，常常會使用-h 之類的東西查看一下簡單的幫助手冊或者說明信息；

對於perl 語言而言，寫起來簡單，常常隨手一寫，解決了當時的問題，可是過幾天去看，你都不知道這個腳本該怎麼調用，是用來作什麼的；

爲了不這樣的狀況，對於經常使用的腳本，有必要提供較爲清晰的幫助文檔。

在perl 裏面，官方提供了這樣的註釋手段，看下面的代碼示例

=pod

=head1 NAME

L<Transdecoder.LongOrfs|http://transdecoder.github.io> - Transcriptome Protein Prediction

=head1 USAGE

Required:

 -t <string>                            transcripts.fasta

Optional:

 --gene_trans_map <string>              gene-to-transcript identifier mapping file (tab-delimited, gene_id<tab>trans_id<return> ) 

 -m <int>                               minimum protein length (default: 100)
 
 -G <string>                            genetic code (default: universal; see PerlDoc; options: Euplotes, Tetrahymena, Candida, Acetabularia)

 -S                                     strand-specific (only analyzes top strand)

=head1 Genetic Codes

See L<http://golgi.harvard.edu/biolinks/gencode.html>. These are currently supported:

 universal (default)
 Euplotes
 Tetrahymena
 Candida
 Acetabularia
 Mitochondrial-Canonical
 Mitochondrial-Vertebrates
 Mitochondrial-Arthropods
 Mitochondrial-Echinoderms
 Mitochondrial-Molluscs
 Mitochondrial-Ascidians
 Mitochondrial-Nematodes
 Mitochondrial-Platyhelminths
 Mitochondrial-Yeasts
 Mitochondrial-Euascomycetes
 Mitochondrial-Protozoans

=cut

=pod 到 =cut 之間的內容是幫助信息，這些信息顯示到屏幕上時是這樣的

NAME
    <Transdecoder.LongOrfs> - Transcriptome Protein Prediction

USAGE
    Required:

     -t <string>                            transcripts.fasta

    Optional:

     --gene_trans_map <string>              gene-to-transcript identifier mapping file (tab-delimited, gene_id<tab>trans_id<return> ) 

     -m <int>                               minimum protein length (default: 100)
 
     -G <string>                            genetic code (default: universal; see PerlDoc; options: Euplotes, Tetrahymena, Candida, Acetabularia)

     -S                                     strand-specific (only analyzes top strand)

Genetic Codes
    See <http://golgi.harvard.edu/biolinks/gencode.html>. These are
    currently supported:

     universal (default)
     Euplotes
     Tetrahymena
     Candida
     Acetabularia
     Mitochondrial-Canonical
     Mitochondrial-Vertebrates
     Mitochondrial-Arthropods
     Mitochondrial-Echinoderms
     Mitochondrial-Molluscs
     Mitochondrial-Ascidians
     Mitochondrial-Nematodes
     Mitochondrial-Platyhelminths
     Mitochondrial-Yeasts
     Mitochondrial-Euascomycetes
     Mitochondrial-Protozoans

有表頭部分，格式上也很整齊，經過=head1 , =pod ， =cut 這幾個小標籤，咱們只須要關注內容，就能夠寫出格式整齊，閱讀良好的幫助信息

use Pod::Usage;

pod2usage(-verbose => 2, -output => \*STDERR) if ($help);

經過使用Pod::Usage 模塊，加能夠將寫好的上述格式的註釋，方便的顯示在屏幕上，結合if 等判斷語句，自定義觸發條件；