Info Catalog gawk: Getline/Variable/Pipe gawk: Getline gawk: Getline/Variable/Coprocess

gawk: Getline/Coprocess

 
 4.10.7 Using 'getline' from a Coprocess
 ---------------------------------------
 
 Reading input into 'getline' from a pipe is a one-way operation.  The
 command that is started with 'COMMAND | getline' only sends data _to_
 your 'awk' program.
 
    On occasion, you might want to send data to another program for
 processing and then read the results back.  'gawk' allows you to start a
 "coprocess", with which two-way communications are possible.  This is
 done with the '|&' operator.  Typically, you write data to the coprocess
 first and then read the results back, as shown in the following:
 
      print "SOME QUERY" |& "db_server"
      "db_server" |& getline
 
 which sends a query to 'db_server' and then reads the results.
 
    The values of 'NR' and 'FNR' are not changed, because the main input
 stream is not used.  However, the record is split into fields in the
 normal manner, thus changing the values of '$0', of the other fields,
 and of 'NF' and 'RT'.
 
    Coprocesses are an advanced feature.  They are discussed here only
 because this is the minor node on 'getline'.  Two-way I/O, where
 coprocesses are discussed in more detail.
 

Info Catalog gawk: Getline/Variable/Pipe gawk: Getline gawk: Getline/Variable/Coprocess