Execute command line and return command output

Question

Currently, I am using shell command line calls from my fortran program using non-standard SYSTEM intrinsic routine (similar to Fortran 2008 EXECUTE_COMMAND_LINE intrinsic):

CALL SYSTEM(commandStr)

where commandStr is a character string containing the shell command I want to execute. At the moment, I am not aware of a direct way to return the output of commandStr, but only its return status. So, what I am doing now is writing output into a file, and then reading the file from within the Fortran program. Example:

CALL SYSTEM('sed ''s/,//g'' myFile > dummyFile')

if I want to remove commas from myFile. I then use OPEN and READ to get contents of dummyFile.

This works just fine, however I am concerned about writing/reading files from disk, especially if I was doing this within a long loop, and if commandStr output was big. Is there a way to re-direct commandStr output into a memory buffer (not hard disk) which I could access from my Fortran program directly (maybe through a specific UNIT number)?

If the output was big, wouldn't it make more sense TO store it to file? — Rook
I guess it would not make a difference for the code - the only part I worry here is frequent I/O to and from disk affecting program efficiency. Is there a reason it would be better to store it to file, something that I am missing? — milancurcic
Well, from my viewpoint it's just a practicality issue. If it's not a lot of data, storing it to a file won't matter. It it is a lot of data, and I'm reusing it in the current running program, the last place where I want it is the memory. I need memory to store the results of "parsing" that file, and then to do something with those. This could've probably been better explained but I think you get the idea. — Rook
I sort of get the feeling you're trying to solve a problem you don't have. — eriktous
@eriktous I agree, what I do now works, but the question still stands, is there a different way to do it? — milancurcic

wallyk wallyk · Accepted Answer · 2011-10-20T16:38:59

If this is in a POSIX environment, the library function popen() might also be available.

iunit = popen ('sed ''s/,//g'' myFile', 'r')

Look at the documentation for your Fortran environment since I'm not sure of the semantics for connecting the i/o to Fortran. If it is like the C runtime library, the file connection also needs a special function to close it, pclose().

Execute command line and return command output

1 Answers