Using getline with No Arguments

The getline command can be used without arguments to read input from the current input file. All it does in this case is read the next input record and split it up into fields. This is useful if you've finished processing the current record, but you want to do some special processing right now on the next record. Here's an example:

awk '{
     if ((t = index($0, "/*")) != 0) {
          # value will be "" if t is 1
          tmp = substr($0, 1, t - 1)
          u = index(substr($0, t + 2), "*/")
          while (u == 0) {
               if (getline <= 0) {
                    m = "unexpected EOF or error"
                    m = (m ": " ERRNO)
                    print m > "/dev/stderr"
                    exit
               }
               t = -1
               u = index($0, "*/")
          }
          # substr expression will be "" if */
          # occurred at end of line
          $0 = tmp substr($0, t + u + 3)
     }
     print $0
}'

This awk program deletes all C-style comments, `/* ... */', from the input. By replacing the `print $0' with other statements, you could perform more complicated processing on the decommented input, like searching for matches of a regular expression. This program has a subtle problem--it does not work if one comment ends and another begins on the same line.

This form of the getline command sets NF (the number of fields; see section Examining Fields), NR (the number of records read so far; see section How Input is Split into Records), FNR (the number of records read from this input file), and the value of $0.

Note: the new value of $0 is used in testing the patterns of any subsequent rules. The original value of $0 that triggered the rule which executed getline is lost (d.c.). By contrast, the next statement reads a new record but immediately begins processing it normally, starting with the first rule in the program. See section The next Statement.

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