Why does sed require 3 backslashes for a regular backslash?

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I was able to reproduce this behavior using Vista and Cygwin 1.7.0.

  • Two backslashes produce the error
  • either three or four backslashes work
  • Five gives the same error

Two backslashes become a single backslash in the shell which then in sed escapes the forward slash which is the middle delimiter.

\\/ -> \/ (which makes the forward slash a regular character instead of a delimiter)

Three of them: The first two become one in the shell which then escape the third one in sed

\\\/ -> \\/

Four: Each pair become single ones in the shell then the first resulting one escapes the second in sed

\\\\/ -> \\/

Edit:

Oh, I forgot to say that both single quotes and double quotes worked the same for me (cmd.exe doesn’t make the distinction that Bash, et al, makes).

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