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The list command (l) displays the contents of the pattern space, showing non-printing characters as two-digit ASCII codes. It is similar in function to the list (:l) command in vi. You can use this command to detect "invisible" characters in the input.[6]
[6] GNU sed displays certain characters, such as carriage return, using the ANSI C escape sequences, instead of straight octal. Presumably, this is easier to comprehend for those who are familiar with C (or awk, as we'll see later in the book).
$ cat test/spchar Here is a string of special characters: ^A ^B ^M ^G