2.7 Emulation

Because of its simularity with join, combine has an emulation mode that allows you to use the syntax of the join command to start combine.

The emulation can be started by using ‘--emulate join’ option as the first option after the command name. After that, you can use the same options you get with join.

For details of the join command, see See (coreutils.info)join invocation section ‘Join Invocation’ in GNU Coreutils Manual. When tested against the test cases packaged with GNU Coreutils, results are identical to join with a couple of exceptions:

• The sort order can be different. combine produces records in the order of the second input file, with any unmatched records from the first input file following in an arbitrary order.
• I change the arguments to the ‘-o’ option in the test script to have quotes around the field order list when it is separated by spaces. combine can handle the space-delimited list, but the standard argument handler getopt_long does not interpret them as a single argument. I don’t see the need to overcome that.
• There is not a specific test, but I have not yet implemented case-insensitive matching. It would have failed if tested.
• One more option that is not implemented in the emulation are the ‘-j1’ and ‘-j2’ methods of specifying separate keys for the two files. Use ‘-1’ and ‘-2’ for that. The two obsolete options would be interpreted as speciying field 1 or field 2 as the common join key, respectively.

There are also a number of features of combine that come through in the emulation. The main features relate to the keys: the sort order of the records in relation to the keys does not matter to combine. combine also allows you to specify a list of key fields (comma-delimited) rather than just one as arguments to ‘-1’, ‘-2’, and ‘-j’. You should make sure that the number of key fields is the same.

Another feature is that the second input file can actually be as many files as you want. That way you can avoid putting the records from several files together if not otherwise necessary.

This document was generated by Daniel P. Valentine on July 28, 2013 using texi2html 1.82.