Linux shell中比较操作符“==”与“-eq”对比

原创作品，允许转载，转载时请务必以超链接形式标明文章原始出处、作者信息和本声明。否则将追究法律责任。 http://dgd2010.blog.51cto.com/1539422/1542048

在Linux shell编程中，经常会用到判断字符串是否相等，可用于判断字符串是否相等的操作符有‘-eq’（相等）, ‘-ne’（不等于）, ‘-lt’（小于）, ‘-le’（小于或等于）, ‘-gt’（大于）或‘-ge’（大于或等于），以及=，==，!=，<，>。

在bash指南中，字母操作符和符号操作符的两端的参数英语表达式不相同，符号操作符用的是string，字母操作符用的是arg。

# http://www.gnu.org/software/bash/manual/bashref.html

string1==string2

string1=string2
True if the strings are equal. ‘=’ should be used with the test command for POSIX conformance.
string1!=string2
True if the strings are not equal.
string1<string2
True ifstring1sorts beforestring2lexicographically.
string1>string2
True ifstring1sorts afterstring2lexicographically.
arg1OParg2
OP is one of ‘-eq’, ‘-ne’, ‘-lt’, ‘-le’, ‘-gt’, or ‘-ge’. These arithmetic binary operators return true ifarg1is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal toarg2, respectively.Arg1andarg2may be positive or negative integers.

在实际编程中发现，当用字母操作符，虽然效果与符号操作符相同，但会产生一个错误提示“[[: arg2: syntax error: operand expected (error token is "arg2")”。

如原文为

 
     
          [[ 
          "$1" 
          -
          eq 
          "" 
          ]] && 
          echo 
          "delete all spaces and comments of specialized file, using with $@ filename" 
          && 
          exit 
          1 
         

   

修改为

 
     
          [[ 
          "$1" 
          == 
          "" 
          ]] && 
          echo 
          "delete all spaces and comments of specialized file, using with $@ filename" 
          && 
          exit 
          1 
         

   

就不再提示了。

附带一个实用小脚本，用途：grep掉空格和注释符（#），简单实用。

 
    
          #!/bin/bash   
         

          # delete all spaces and comments of specialized file, using with $@ filename    
         
 
          [[ 
          "$1" 
          == 
          "" 
          ] && 
          echo 
          "delete all spaces and comments of specialized file, using with $@ filename" 
          && 
          exit 
          1     
         
 
          grep 
          -
          v 
          \
          # $1 | grep -v ^$ 
         

   

添加到操作系统中：

 
          cat 
          > delsc.sh << eof    
         
          #!/bin/bash    
         
          # delete all spaces and comments of specialized file, using with $@ filename    
         
          [[ 
          "\$1" 
          -== 
          "" 
          ]] && 
          echo 
          "delete all spaces and comments of specialized file, using with \$@ filename" 
          && 
          exit 
          1     
         
          grep 
          -
          v 
          \
          # \$1 | grep -v ^$     
         
          eof    
         
          chmod 
          +x .
          /delsc
          .sh     
         
          \
          mv 
          delsc.sh 
          /usr/local/bin/delsc    
         
          which 
          delsc     
         
          cat 
          /usr/local/bin/delsc

用法：

 
          delsc filename

本文出自 “通信，我的最爱” 博客，请务必保留此出处http://dgd2010.blog.51cto.com/1539422/1542048