In addition to writing to and reading from files, you can perform a variety of tests on files.
The following process rule will fire only when the file "foo.txt" exists:
If you want to do one thing when the file exists and another if it doesn't exist, you can use the test in a "do...done" block:
process do when file "foo.txt" exists reopen foo put foo "Its fleece was white as snow.%n" close foo else open foo as file "foo.txt" put foo "Mary had a little lamb,%n" close foo done
You can also test for the readability and writability of a file as follows:
process when file "foo.txt" isnt readable output "File foo.txt cannot be read.%n" || "Check your file and directory permissions.%n" process when file "foo.txt" isnt writable output "File foo.txt cannot be written.%n" || "Check your file and directory permissions.%n"
The results of these tests can be reversed by using
is rather than
Finally, you can test whether a named file is a file or a directory:
process when file "foo.txt" is file submit file "foo.txt" process when file "foo.txt" is directory output "Error: foo.txt is a directory.%n"
These tests can also be reversed by replacing
File tests are not often needed in OmniMark programs because the default handling of file input and output errors is often appropriate. If an error is encountered when attempting to read from or write to a file, OmniMark will generate an error message that specifies the error encountered and the name of the file involved. The program then terminates.
Error messages will be generated when any of the following problems are encountered:
File tests exist so that you can specify different handling procedures for file input and output errors.