请尝试以下操作（仅使用提供的样品进行测试）。

awk 'BEGIN{s1="\"";FS=OFS="~"} {for(i=1;i<=NF;i++){if($i!~/^\"|\"$/){$i=s1 $i s1}}} 1' Input_file

输出如下。

"eno"~"ename"~"address"~"zip"
"123"~"abc"~""~"560000"
"245"~"abc ~ def"~"hyd"~"560102"
"333"~"ghi~jkl"~"pub"~"560103"

***说明：***现在添加上述代码的说明。

awk '                       ##Starting awk program here.
BEGIN{                      ##Starting BEGIN section of awk program here.
  s1="\""                   ##Setting variable s1 to " here.
  FS=OFS="~"                ##Setting value of FS and OFS as ~ here.
}                           ##Closing BEGIN block of awk code here.
{
  for(i=1;i<=NF;i++){       ##Starting for loop here from i=1 to till value of NF here.
    if($i!~/^\"|\"$/){      ##Checking condition of value of current field is NOT having s1 value in it.
      $i=s1 $i s1           ##Adding s1 variable before and after the value of $i.
    }                       ##Closing block for if condition.
  }                         ##Closing block for for loop here.
}                           ##Closing main block here.
1                           ##Mentioning 1 will print the lines of Input_file.
'  Input_file               ##mentioning Input_file name here.

在这里，您可以将FPAT与gnu awk配合使用

awk -v FPAT='([^~]*)|("[^"]+")' -v OFS="~" '{for (i=1;i<=NF;i++) if ($i!~/^\"/) $i="\""$i"\""} 1' file
"eno"~"ename"~"address"~"zip"
"123"~"abc"~""~"560000"
"245"~"abc ~ def"~"hyd"~"560102"
"333"~"ghi~jkl"~"pub"~"560103"

我们不告诉字段分隔符的样子，而是告诉字段的样子。然后测试字段是否没有双引号，如果没有，就添加它。
然后，您可以根据需要轻松更改字段分隔符：

awk -v FPAT='([^~]*)|("[^"]+")' -v OFS="," '{for (i=1;i<=NF;i++) if ($i!~/^\"/) $i="\""$i"\""} 1' file
"eno","ename","address","zip"
"123","abc","","560000"
"245","abc ~ def","hyd","560102"
"333","ghi~jkl","pub","560103"