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fScan Reference Manual, Chapter 1 (Topics): status
Status queries -- Command operators to query data status
fScan command lines and interactive command strings can contain special query operators that test the status of data elements. The queries return either a 1 or 0 value, depending on whether the query result was yes or no.
The data definition query -- ?
usage: ?data
The '?' query operator can be used in place of the '$' data name identifier in any fScan command string.
The value of a query is:
-1 if the DATA name is not defined
0 if the DATA name is defined but empty (string data only)
1 if the DATA name is defined and not an empty string.
This is different than the '$' operator, which is replaced by the actual value of the named DATA.
The file found query -- ?exists
usage: ?exists(filename)
or: $exists(filename)
The EXISTS query operator test whether its argument string is the name of an existing data file. It returns 1 if the file was found, 0 if the file was not found.
See Also:
IF
