(ed.info)Line addressing

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Enter node , (file) or (file)node

4 Line addressing
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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 address of the last line of the
file. In general, the current address is set to the address of the last
line affected by a command.

   One exception to the rule that addresses represent line numbers is
the address '0' (zero). This means "at the beginning of the buffer",
and is valid wherever it makes sense.

   An address range is two addresses separated either by a comma (',')
or a semicolon (';'). 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. The value of the first address in a range cannot exceed the
value of the second.

   Addresses can be omitted on either side of the comma or semicolon
separator. If only the first address is given in a range, then the
second address is set to the given address. If only the second address
is given, the resulting address pairs are '1,addr' and '.;addr'
respectively. If a 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. It is an error to give any number of addresses to a command that
requires zero addresses.

   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.

'?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.

''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:

   * '+' 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.

   * A number adds the indicated number of lines to the address.


   It is not an error if an intermediate address value is negative or
greater than the address of the last line in the buffer. It is an error
if the final address value is negative or greater than the address of
the last line in the buffer. It is an error if a search for a RE fails
to find a matching line.