grep で tab を検索する

grep $'\t' ${filename}

man bash より抜粋

       Words  of  the  form  $'string' are treated specially.  The word expands to string, with backslash-escaped characters replaced as
       specified by the ANSI C standard.  Backslash escape sequences, if present, are decoded as follows:
              \a     alert (bell)
              \b     backspace
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \'     single quote
              \"     double quote
              \nnn   the eight-bit character whose value is the octal value nnn (one to three digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
              \cx    a control-x character

       The expanded result is single-quoted, as if the dollar sign had not been present.