perl基础知识02【代码执行格式】

[oracle@localhost ~]$ perl --help

Usage: perl [switches] [--] [programfile] [arguments]
  -0[octal]       specify record separator (\0, if no argument)
  -a              autosplit mode with -n or -p (splits $_ into @F)
  -C[number/list] enables the listed Unicode features
  -c              check syntax only (runs BEGIN and CHECK blocks)
  -d[:debugger]   run program under debugger
  -D[number/list] set debugging flags (argument is a bit mask or alphabets)

  -e program      one line of program (several -e's allowed, omit programfile)

#这个参数也常用，当在后面执行命令行时；如

[oracle@localhost ~]$ perl -e' print "ok\n"'
ok

  -f              don't do $sitelib/sitecustomize.pl at startup
  -F/pattern/     split() pattern for -a switch (//'s are optional)

  -i[extension]   edit <> files in place (makes backup if extension supplied)

#直接在原文件上做修改！做时记得做个备份

  -Idirectory     specify @INC/#include directory (several -I's allowed)
  -l[octal]       enable line ending processing, specifies line terminator
  -[mM][-]module  execute "use/no module..." before executing program

  -n              assume "while (<>) { ... }" loop around program

#当作是循环，此选项经常使用，假定一个文本有10行内容，那么如果要处理这10行，你就要加上此参数；

  -p              assume loop like -n but print line also, like sed

#暂时未看出是什么用处的

  -P              run program through C preprocessor before compilation

#在编译之前通过C预处理器运行

  -s              enable rudimentary parsing for switches after programfile

#待确定

  -S              look for programfile using PATH environment variable

#它会去$PATH目录中去寻找你要执行的程序，而不会在默认的当前目录

  -t              enable tainting warnings

#开启损坏警告

  -T              enable tainting checks

#开启损坏核对

  -u              dump core after parsing program

[oracle@localhost ~]$ cat perl01
#!/usr/bin/perl
print "what\n";
[oracle@localhost ~]$ perl -u perl01
Aborted

  -U              allow unsafe operations

  -v              print version, subversion (includes VERY IMPORTANT perl info)

#直接输入perl -v 输出版本信息

  -V[:variable]   print configuration summary (or a single Config.pm variable)

#：直接输入perl -V 输出配置汇总

  -w              enable many useful warnings (RECOMMENDED)

[oracle@localhost ~]$ cat perl01
#!/usr/bin/perl
print what;

[oracle@localhost ~]$ perl perl01
[oracle@localhost ~]$  perl -w perl01  #因为没有在print内容上加引号的告警,虽然直接执行没有报错！
Unquoted string "what" may clash with future reserved word at perl01 line 2.
Name "main::what" used only once: possible typo at perl01 line 2.
print() on unopened filehandle what at perl01 line 2.

  -W              enable all warnings  #同上 (-w)

  -x[directory]   strip off text before #!perl line and perhaps cd to directory

#格式类似于：perl -xzbkdir  perl01  #其中zbkdir为一目录名，具体用处还不详；

  -X              disable all warnings

[oracle@localhost ~]$ perl -X perl01
[oracle@localhost ~]$
[oracle@localhost ~]$ cat perl01
use warnings;
#!/usr/bin/perl
print what;
[oracle@localhost ~]$ perl perl01
Unquoted string "what" may clash with future reserved word at perl01 line 3.
Name "main::what" used only once: possible typo at perl01 line 3.
print() on unopened filehandle what at perl01 line 3.
[oracle@localhost ~]$ perl -X perl01  #忽略里边use warnings的告警提示;

兴例：

（1）-ne

[oracle@localhost ~]$ cat >01.txt
first
second
third

[oracle@localhost ~]$
[oracle@localhost ~]$ perl -e '
> print;
> ' 01.txt
[oracle@localhost ~]$
[oracle@localhost ~]$ perl -ne'
> print;
> ' 01.txt
first
second
third
[oracle@localhost ~]$
#可以看到只有加入了-n选项后才能将文中的内容循环的输出；

（2）-i

#在原文件基础上直接修改

[oracle@localhost ~]$ perl -i -ne'
> s/first/last/ig;
> print;
> ' 01.txt
[oracle@localhost ~]$ cat 01.txt
last
second
third

#以上操作要切记备份，以免悲剧发生！