Menu
Now I want to find whether there are lines containing '\' character. I tried grep "\\" XXFile but it hints "Trailing Backslash". But when I tried grep '\\' XXFile it is OK. Could anyone explain why the first case cannot run? Thanks.
831
Grep then sees a backslash with no following character, so it emits a "trailing backslash" warning. If you want to use double quotes you need to apply two levels of escaping, one for the shell and one for grep. The result: "\\\\" .
Escaping Special Characters However, sometimes you will need to include an exact, or literal, instance of these characters in your grep pattern. In this case, you must use the backslash character \ before that special character to have it be treated literally; this is known as "escaping" the special character.
If you include special characters in patterns typed on the command line, escape them by enclosing them in single quotation marks to prevent inadvertent misinterpretation by the shell or command interpreter. To match a character that is special to grep –E, put a backslash ( \ ) in front of the character.
The forward slash is not a special character in grep, but may be in tools like sed, Ruby, or Perl. You probably want to escape your literal periods, though, and it does no harm to escape the slash. This should work in all cases: \.
The difference is in how the shell treats the backslashes:
When you write "\\" in double quotes, the shell interprets the backslash escape and ends up passing the string \ to grep. Grep then sees a backslash with no following character, so it emits a "trailing backslash" warning. If you want to use double quotes you need to apply two levels of escaping, one for the shell and one for grep. The result: "\\\\".
When you write '\\' in single quotes, the shell does not do any interpretation, which means grep receives the string \\ with both backslashes intact. Grep interprets this as an escaped backslash, so it searches the file for a literal backslash character.
If that's not clear, we can use echo to see exactly what the shell is doing. echo doesn't do any backslash interpretation itself, so what it prints is what the shell passed to it.
$ echo "\\" \ $ echo '\\' \\ If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
