The NCEP cwordsh utility

At its most basic level, a BUFR file is just a stream of bits encoded according to a set of rules as spelled out within WMO Manual #306 More to the point, this type of file structure is not very conducive to interaction with standard FORTRAN, which is the language in which the the BUFRLIB software is written, because standard FORTRAN, unlike certain other programming languages such as C and C++, does not have the capability to read or write data to or from a system file as a pure binary stream of bits. And, while it's true that some vendors of FORTRAN compilers do provide their own non-standard extensions to allow such a capability, this is by no means universal across all of the many available UNIX platforms in existence today. This dilemna is the primary reason why the BUFRLIB software leaves the actual FORTRAN "OPEN" of BUFR files up to each individual application program, because the "OPEN" statement is where a file's organization and access mode (via the "FORM=" attribute) are specified; thus, users who are fortunate enough to be operating on a platform which provides the capability to access a file as a binary stream can easily do so for their BUFR files when using the BUFRLIB software. The question, then, is what can the rest of us, for whom the best available option in standard FORTRAN is often the FORM='UNFORMATTED' access mode, do to get around this problem? We could, of course, use the available BUFRLIB subroutines READERME and WRITSA in order to read/write BUFR messages directly from/to an array in FORTRAN memory, which could then be redirected to a C function in order to actually interact with the local filesystem, but this approach leads to a loss of overall flexibility in how application programs can interface with the BUFRLIB software. Instead, the better (and more portable!) solution is to use a separate utility that can translate back-and-forth between a pure BUFR file and one that contains FORTRAN-blocking information, and which can thus be interfaced to the BUFRLIB software via the universally-supported FORM='UNFORMATTED' access mode! By making use of such a utility, an application program that writes BUFR messages directly to a file (via, e.g., subroutine WRITSB) can use the FORM='UNFORMATTED' attribute in the FORTRAN "OPEN" statement for that file and then, subsequently, remove the FORTRAN-blocking information generated by that attribute and thereby obtain a pure, unblocked BUFR bit stream. Likewise, an application program that wished to directly read a pure, unblocked BUFR file (via, e.g., subroutine READMG) could first FORTRAN-block the file using this special utility, and then the subsequent use of FORM='UNFORMATTED' would allow that file to be read by the BUFRLIB software. Thankfully, such a utility does exist, and its name is cwordsh!

To use the cwordsh utility, it must first be compiled on the platform on which it is to be run, and this obviously should be the same platform upon which the application program is run which uses the BUFRLIB software in order to read or write the related BUFR file. In addition, note that, while cwordsh is not itself directly a part of BUFRLIB, it does make use of several BUFRLIB subroutines, and therefore the BUFRLIB software must have already been compiled at the time that cwordsh is compiled so that it can be object-linked during the compilation. However, once this is done, we now have a utility that can alternately FORTRAN-block and unblock BUFR files that are created using the BUFRLIB software!

The NCEP cwordsh utility is freely available, subject to the terms of the usual NWS disclaimer, and is downloadable as a tarfile cwordsh.tar. After downloading and unpacking (via "tar xvf") this tarfile, read and follow the instructions in the extracted file "README_cwordsh" in order to compile and run the utility.