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   awk.1p    ( 1 )

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Стандартный ввод (Stdin)

The standard input shall be used only if no file operands are
       specified, or if a file operand is '-', or if a progfile option-
       argument is '-'; see the INPUT FILES section. If the awk program
       contains no actions and no patterns, but is otherwise a valid awk
       program, standard input and any file operands shall not be read
       and awk shall exit with a return status of zero.