grep: Trailing backslash

The backslash is a special character for many applications:

  • including the shell: you need to escape it using another backslash or more elegantly, using single quotes when possible:

    $ printf '%s\n' foo\\bar 'foo\bar'
    foo\bar
    foo\bar
    

    Here the command received two arguments with value foo\bar, which were echoed as-is on the terminal.

    (Above, I used printf instead of echo as many echo implementations also do their own interpreting of backslash (here would expand \b into a backspace character)).

  • But backslash is also a special character for grep. This command recognizes many special sequences like \(, \|, \., and so on. So similarly you need to feed grep with a double \\ for an actual backslash character. This means that using the shell you need to type:

    grep 'foo\\bar'
    

    or equivalently:

    grep foo\\\\bar
    

    (both lines tell the shell to transmit foo\\bar as argument to grep).

  • Many other commands interpret backslashes in some of their arguments… and two levels of escaping are needed (one to escape the shell interpretation, one to escape the command interpretation).


By the way, for the shell, single quotes '…' prevent any kind of character interpretation, but double quotes only prevents some of them: in particular $, ` and \ remain active characters within "…".


You can also use fgrep (which is just grep with the -F flag). This forces grep to interpret the pattern as a fixed string (i.e. it'll treat a \ as a literal \). You'll still need to protect the backslashes from expansion by the shell.

grep -F '\resources\'

grep requires four backslashes to represent a backslash:

grep "\\\\resources\\\\"