awk中单引号和双引号之间的区别 [英] Difference between single and double quotes in awk

问题描述

我有这个awk声明:

glb_library="my_library"
awk "
        /^Direct Dependers of/ { next }
        /^---/                 { next }
        /^$glb_library:/       { ver=\$0; next }
                               { gsub(/[[:space:]]/, '', \$0); print ver':'\$0 }
      " file

基本上，我已经将awk代码括在双引号中，以便扩展外壳变量glb_library.我已确保转义$字符以防止外壳扩展$0.遵循了此处的指导.

Basically, I have enclosed the awk code in double quotes so that the shell variable glb_library is expanded. I have made sure to escape the $ character to prevent the shell from expanding $0. Followed the guidance from here.

awk给我这个错误:

awk: syntax error at source line 5
 context is
                                   { gsub(/[[:space:]]/, >>>  ' <<<

我想了解:

• 在awk中使用单引号是否合法?为什么''不是像""这样的空字符串?
• awk处理单引号和双引号是否不同?

• Is it legal to use single quotes inside awk? Why is '' not a null string like "" is?
• Does awk treat single and double quotes differently?

在用反斜杠转义单引号并使用\"\"表示空字符串而不是''之后，我的代码工作了.

My code worked after I escaped the single quotes with backslashes and used \"\" to represent the null string instead of ''.

推荐答案

基于awk专家的上述评论和一些研究，我正在发布此答案:

Based on the comments above by awk experts and some research, I am posting this answer:

• awk字符串用双引号而不是单引号引起来；更准确地说: 单引号不是awk中的字符串定界符，与shell不同
• awk对单引号没有特殊含义，并且如果用于字符串文字中，则必须将其用双引号引起来
• 最好使用单引号在命令行上包装awk语句，这与OP的代码使用双引号不同(Ed明确指出了这一点)

进一步澄清:

• ""是awk中的空字符串，不是''
• 要在awk字符串文字中使用单引号，请使用双引号将其引起来，如"Ed's answers are great!"

• 在awk中处理单引号时遵循的其他技术是:

• "" is the null string in awk, not ''
• to use single quotes in an awk string literal, enclose them in double quotes, as in "Ed's answers are great!"

• other techniques followed while handling single quotes in awk are:

a)使用变量，如awk -v q="'" '{ print q }' ...

b)使用八进制或十六进制表示法，如awk '{ print "\047"$0"\047" }' ...

b) use octal or hex notation, as in awk '{ print "\047"$0"\047" }' ...

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