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 4.9.3 Using `getline' from a File
 ---------------------------------
 
 Use `getline < FILE' to read the next record from FILE.  Here FILE is a
 string-valued expression that specifies the file name.  `< FILE' is
 called a "redirection" because it directs input to come from a
 different place.  For example, the following program reads its input
 record from the file `secondary.input' when it encounters a first field
 with a value equal to 10 in the current input file:
 
      {
          if ($1 == 10) {
               getline < "secondary.input"
               print
          } else
               print
      }
 
    Because the main input stream is not used, the values of `NR' and
 `FNR' are not changed. However, the record it reads is split into
 fields in the normal manner, so the values of `$0' and the other fields
 are changed, resulting in a new value of `NF'.
 
    According to POSIX, `getline < EXPRESSION' is ambiguous if
 EXPRESSION contains unparenthesized operators other than `$'; for
 example, `getline < dir "/" file' is ambiguous because the
 concatenation operator is not parenthesized.  You should write it as
 `getline < (dir "/" file)' if you want your program to be portable to
 all `awk' implementations.
 
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