File: sed.info,  Node: Numeric Addresses,  Next: Regexp Addresses,  Prev: Addresses overview,  Up: sed addresses

4.2 Selecting lines by numbers
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Addresses in a ‘sed’ script can be in any of the following forms:
‘NUMBER’
     Specifying a line number will match only that line in the input.
     (Note that ‘sed’ counts lines continuously across all input files
     unless ‘-i’ or ‘-s’ options are specified.)

‘$’
     This address matches the last line of the last file of input, or
     the last line of each file when the ‘-i’ or ‘-s’ options are
     specified.

‘FIRST~STEP’
     This GNU extension matches every STEPth line starting with line
     FIRST.  In particular, lines will be selected when there exists a
     non-negative N such that the current line-number equals FIRST + (N
     * STEP).  Thus, one would use ‘1~2’ to select the odd-numbered
     lines and ‘0~2’ for even-numbered lines; to pick every third line
     starting with the second, ‘2~3’ would be used; to pick every fifth
     line starting with the tenth, use ‘10~5’; and ‘50~0’ is just an
     obscure way of saying ‘50’.

     The following commands demonstrate the step address usage:

          $ seq 10 | sed -n '0~4p'
          4
          8

          $ seq 10 | sed -n '1~3p'
          1
          4
          7
          10