perl 里面如何写出阅读友好的代码提示

在咱们使用别人写好的程序时，常常会使用-h 之类的东西查看一下简单的帮助手册或者说明信息；

对于perl 语言而言，写起来简单，常常随手一写，解决了当时的问题，可是过几天去看，你都不知道这个脚本该怎么调用，是用来作什么的；

为了不这样的状况，对于经常使用的脚本，有必要提供较为清晰的帮助文档。

在perl 里面，官方提供了这样的注释手段，看下面的代码示例

=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 之间的内容是帮助信息，这些信息显示到屏幕上时是这样的

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

有表头部分，格式上也很整齐，经过=head1 , =pod ， =cut 这几个小标签，咱们只须要关注内容，就能够写出格式整齐，阅读良好的帮助信息

use Pod::Usage;

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

经过使用Pod::Usage 模块，加能够将写好的上述格式的注释，方便的显示在屏幕上，结合if 等判断语句，自定义触发条件；