matlabfopendev-null

Is there a null device in Matlab?


I'm trying to find an easy way to turn logging to a text file on and off much like the example seen here in Python. Their solution was to use a valid file name where logging is desired and to use the null device 'dev/null' otherwise. They're using redirection but I wish to use fopen.

Is there some way to do something like the following, which word work for Unix or Windows systems if that matters.

nullFID = fopen('/dev/nul', 'w')

The script I'm altering could benefit greatly with detailed logging in certain breaking scenarios where we want to pull up a fine level of detail for a handful of files but that would otherwise grow too large for the batch processing the script normally targets.


Solution

  • Looks like this can be done, someone posted an answer on MathWorks using a similar term of "null file". Not sure if that's valid terminology but could be a shortening of "null device file".

    The way to reference the null device is OS dependent...

    nullFID = fopen( 'NUL:'    ); % Windows
    nullFID = fopen('/dev/null'); % UNIX
    

    And it also appears the reference varies from Matlab releases. Consider the following script

    ver
    nullFID = fopen( 'NUL:' , 'w' )
    fprintf( nullFID , '12345' )
    nullFID = fopen( 'NUL:'  )
    fprintf( nullFID , '12345' )
    nullFID = fopen('NUL' , 'w' )
    nullFID = fopen('NUL' )
    

    And the following output generated from two versions of Matlab...

    R2011b

    >> ver
    -------------------------------------------------------------------------------------
    MATLAB Version 7.13.0.564 (R2011b)
    MATLAB License Number: xxxx
    Operating System: Microsoft Windows 7 Version 6.1 (Build 7601: Service Pack 1)
    Java VM Version: Java 1.6.0_17-b04 with Sun Microsystems Inc. Java HotSpot(TM) 64-Bit Server VM mixed mode
    -------------------------------------------------------------------------------------
    MATLAB                                                Version 7.13       (R2011b)
    
    >> nullFID = fopen( 'NUL:' , 'w' )
    nullFID = 119
    
    >> fprintf( nullFID , '12345' )
    ans = 5
    
    >> nullFID = fopen( 'NUL:' )
    nullFID = 120
    
    >> fprintf( nullFID , '12345' )
    ans = 0
    
    >> nullFID = fopen('NUL' , 'w' )
    Warning: You have chosen a reserved DOS device name for your filename.
    Please choose another valid filename
    nullFID = -1
    
    >> nullFID = fopen('NUL')
    nullFID = -1
    

    R2015a

    >> ver
    ----------------------------------------------------------------------------------------------------
    MATLAB Version: 8.5.0.197613 (R2015a)
    MATLAB License Number: 1093113
    Operating System: Microsoft Windows 7 Professional  Version 6.1 (Build 7601: Service Pack 1)
    Java Version: Java 1.7.0_60-b19 with Oracle Corporation Java HotSpot(TM) 64-Bit Server VM mixed mode
    ----------------------------------------------------------------------------------------------------
    MATLAB                                                Version 8.5        (R2015a)
    
    >> nullFID = fopen( 'NUL:' , 'w' )
    nullFID = -1
    
    >> fprintf( nullFID , '12345' )
    Error using fprintf
    Invalid file identifier. Use fopen to generate a valid file identifier.
    
    >> nullFID = fopen( 'NUL:' )
    nullFID = 8
    
    >> fprintf( nullFID , '12345' )
    ans = 0
    
    >> nullFID = fopen('NUL' , 'w' )
    Warning: You have chosen a reserved DOS device name for your filename.
    Please choose another valid filename. 
    nullFID = -1
    
    >> nullFID = fopen('NUL' )
    nullFID = -1