(ed.info.gz) Line Addressing

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 4 Line Addressing
 *****************
 
 An address represents the number of a line in the buffer. `ed'
 maintains a "current address" which is typically supplied to commands
 as the default address when none is specified. When a file is first
 read, the current address is set to the last line of the file. In
 general, the current address is set to the last line affected by a
 command.
 
    One exception to the rule that addresses represent line numbers is
 the address `0' (zero). This means "before the first line", and is
 valid wherever it makes sense.
 
    An address range is two addresses separated either by a comma (`,')
 or a semicolon (`;'). The value of the first address in a range cannot
 exceed the value of the second. If only one address is given in a
 range, then the second address is set to the given address. If an
 N-tuple of addresses is given where N > 2, then the corresponding range
 is determined by the last two addresses in the N-tuple. If only one
 address is expected, then the last address is used.
 
    In a semicolon-delimited range, the current address (`.') is set to
 the first address before the second address is calculated. This feature
 can be used to set the starting line for searches.
 
    A line address is constructed as follows:
 
 `.'
      The current line (address) in the buffer.
 
 `$'
      The last line in the buffer.
 
 `N'
      The Nth line in the buffer, where N is a number in the range `0,$'.
 
 `+N'
      The Nth next line, where N is a non-negative number.
 
 `-N'
      The Nth previous line, where N is a non-negative number.
 
 `+'
      The next line. This is equivalent to `+1' and may be repeated with
      cumulative effect.
 
 `-'
      The previous line. This is equivalent to `-1' and may be repeated
      with cumulative effect.
 
 `,'
      The first through last lines in the buffer. This is equivalent to
      the address range `1,$'.
 
 `;'
      The current through last lines in the buffer. This is equivalent
      to the address range `.,$'.
 
 `/RE/'
      The next line containing the regular expression RE. The search
      wraps to the beginning of the buffer and continues down to the
      current line, if necessary. `//' repeats the last search.
 
 `?RE?'
      The previous line containing the regular expression RE. The search
      wraps to the end of the buffer and continues up to the current
      line, if necessary. `??' repeats the last search.
 
 `'x'
      The apostrophe-x character pair addresses the line previously
      marked by a `k' (mark) command, where `x' is a lower case letter
      from the portable character set.
 
 
    Addresses can be followed by one or more address offsets, optionally
 separated by whitespace. Offsets are constructed as follows:
 
    * A number adds the indicated number of lines to the address.
 
    * `+' or `-' followed by a number adds or subtracts the indicated
      number of lines to or from the address.
 
    * `+' or `-' not followed by a number adds or subtracts 1 to or from
      the address.
 
 

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