Awk - field separator behavior

问题

I have a file:

CreateSec,explorer.exe,\\WINDOWS\\system32\\verclsid.exe,SUCCESS

I want to print "$2"

Example 1

It works well:

$ awk -F '\\\\\\\\' '{print $2}' file
WINDOWS

Example 2

It works well:

$ awk -F '\\\\'+ '{print $2}' file
WINDOWS

Example 3

Does not print.

$ awk -F "\\\\\\\\" '{print $2}' file
.

Example 4

So it works well:

$ echo "CreateSec,explorer.exe,\\WINDOWS\\system32\\verclsid.exe,SUCCESS" | awk -F '\' '{print $2}'
WINDOWS
----------------------------------------------------------------------------------

$ echo "CreateSec,explorer.exe,\\WINDOWS\\system32\\verclsid.exe,SUCCESS" | awk -F "\\" '{print $2}'
WINDOWS

Questions:

1. Why 3 example does not work?
2. How to properly save 3 example?

3. What is the difference between?:

   a) awk -F '\\\\\\\\'

   b) awk -F "\\\\\\\\"

Thank you for the explanation.

回答1:

Regarding (3) — four backslashes is the difference:

• Inside single quotes, there are no metacharacters, so the shell passes 8 backslashes to awk.
• Inside double quotes, the backslash escapes the following character, so the shell passes 4 backslashes to awk.

来源：https://stackoverflow.com/questions/13609479/awk-field-separator-behavior