Multiline Pattern Space

We have emphasized in previous discussions of regular expressions that pattern matching is line-oriented. A program like grep attempts to match a pattern on a single line of input. This makes it difficult to match a phrase, for instance, which can start at the end of one line and finish at the beginning of the next line. Other patterns might be significant only when repeated on multiple lines.

Sed has the ability to look at more than one line in the pattern space. This allows you to match patterns that extend over multiple lines. In this section, we will look at commands that create a multiline pattern space and manipulate its contents. The three multiline commands (N,D,P) all correspond to lowercase basic commands (n,d,p) that were presented in the previous chapter. The Delete (D) command, for instance, is a multiline version of the delete command (d). The difference is that while d deletes the contents of the pattern space, D deletes only the first line of a multiline pattern space.

Append Next Line

The multiline Next (N) command creates a multiline pattern space by reading a new line of input and appending it to the contents of the pattern space. The original contents of pattern space and the new input line are separated by a newline. The embedded newline character can be matched in patterns by the escape sequence “\n”. In a multiline pattern space, the metacharacter “^” matches the very first character of the pattern space, and not the character(s) ...

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