Softlink is a tool to provide easy, portable use of standard Starlink include files on Unix systems. It is complementary to FORCONV and will be of general use when developing Fortran programs on Unix as well as in porting code to Unix.
Starlink Fortran programs frequently make use of INCLUDE files to define symbolic constants or
common blocks. When the INCLUDE file is one supplied by Starlink, a logical name is
defined on VMS to point to the file. For example, the logical name SAE_PAR points to the file
LIB_COMMON_DIR:SAE_PAR.FOR. This means that the file can be included in a Fortran program with the
statement:
There is no need to refer to the location of the file, just to its name. This makes the program more portable than referring to the explicit file.
Unix does not provide logical names, but you can achieve a similar effect by the use of soft links. A soft link looks like a file in a directory, but is actually just a pointer to another file. To use a soft link to refer to the INCLUDE file in the above example, you would type:
This command should be executed in the same directory as the source of the Fortran program. If you are working on Fortran programs in different directories, you will need the appropriate soft links in each directory. This is unlike VMS, where logical names exist independently of the file system. Note that the name of the file is in lower case, but the name in the include statement is in upper case. This distinction is important as Unix is case sensitive, unlike VMS.
Softlink is a Unix shell script that can be used to create and remove soft links to files. The purpose of writing it was to automate the setting up of soft links that point to standard Starlink Fortran include files. Rather than having programs contain lines like:
they will contain lines like:
and a soft link to the file /star/include/sae_par will be created in the directory containing the source
code. This makes the source code more portable; it may well run on Unix and VMS systems with no
changes.
Before compiling a program on a Unix system, the soft links to the include files should be created. This need only be done once as the soft links are permanent. For the above example, you would type:
Note that the name of the file being pointed to must match the name of the file in the Fortran INCLUDE statement for softlink to be effective. If the names are different, then you should either set up the soft link by hand, or use FORCONV.
Softlink accepts three arguments. Only the first one is mandatory. This specifies the full path name of
the file that the soft link will point to. An example is /star/include/sae_par.
The second (optional) argument specifies whether the name of the soft link is in upper or lower
case. If it is omitted (or given as the null string), then the name of the soft link matches
exactly the name of the file that it points to. The value of the argument can be one of ‘lower’,
‘upper’, ‘both’, ‘all’ or ‘remove’. A value of ‘lower’ specifies that the name of the soft link
will be in lower case and a value of ‘upper’ specifies that the name of the soft link will
be in upper case. A value of ‘both’ specifies that two soft links are to be created, one in
lower case and one in upper case. A value of ‘all’ specifies that links will be created in
lower case, upper case and with the same name as the file that it is pointing to if that is
not purely lower case or upper case. If the argument is ‘remove’, then all the soft links are
removed. The script checks to see that it is only removing soft links and not files of the same
name.
The third argument is normally absent. If it is present, then the script does not execute any commands to create soft links, but writes those command to the file named by the third argument. For example, the command
will create a file called fred containing the lines:
If the output file already exists, then the commands are appended to the file so that a set of link
commands can be built up. If the name of the output file is mfile, then the commands are output in a
form suitable for inclusion in a make file. In particular, the first character of each line is a tab
character.
When writing programs that call Starlink libraries, you will find yourself setting up the same soft links over and over again. To ease this process, shell scripts are provided to define the soft links for all of the Starlink subroutine libraries. The scripts are called lib_dev, e.g. to set up the soft links needed when writing a program that calls FIO, just type:
The soft links can be removed by typing:
The scripts provide fewer functions than the softlink script. All links are created in upper case and the
only option is remove, which does not check to see that the names referred to are soft link rather than
files. To offset these restrictions, the lib_dev scripts run faster than they would if they provided all the
features of softlink. The list of scripts is as follows:
| Package | Script |
| AGI | agi_dev |
| ARY | ary_dev |
| CHR | chr_dev |
| EMS | ems_dev |
| ERR | err_dev |
| FIO | fio_dev |
| GKS | gks_dev |
| GNS | gns_dev |
| GRP | grp_dev |
| GWM | gwm_dev |
| HDS | hds_dev |
| IDI | idi_dev |
| NDF | ndf_dev |
| PAR | par_dev |
| PRIMDAT | prm_dev |
| PSX | psx_dev |
| REF | ref_dev |
| SGS | sgs_dev |
| TRANSFORM | trn_dev |
There are also scripts star_dev, which creates the soft links to SAE_PAR, and adam_dev, which creates
the soft links needed when writing programs that call the internals of ADAM.