Implication of using a GPL'd software

[NitinGupta]

For one of my softwares am trying to understand the implications of using a GPL software. For my software i need some symbolic computation like provided by GPL'd CAS like Maxima( http://maxima.sourceforge.net/ ).Right now ,my program is communicating with Maxima through files i.e my program invokes maxima through a shell command and provides input files.Maxima gives output files and my program was parses them for results.So here i have my first question

1) If a program is just communicating to a GPL'd program through files.Does this program still needs to be released under GPL ? My program and GPL program are separately installed and there are no common structures/headers used by them.So can i release my program close-sourced and ask for a fee for commercial usage ?

2) communication through files is too slow.Another approach can be of starting GPL'd program (maxima in my case) in server mode and my program commuicating to it over sockets.So if i do that, will it require me to release my program under GPL ? I understand that there can be different answers depending on HOW exactly we communicate to a GPL program over sockets. But am pretty confused over this.Please help.

[khattam_]

About the 1st question:

You can even charge for GPLed software. You can of course charge for your software which just communicates with another GPLed software.

Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for them if you wish),

You need not release it under GPL.

Please read the GPL http://www.gnu.org/copyleft/gpl.html

[NitinGupta]

Thanks. Actually here am trying to understand the finer details of what's the limit of interaction with a GPL'd software, which'll still let me release my program closed-source and not under GPL.In first case(of communication thru files) i am not static/dynamic linking to GPL software so i guess i am safe ? Am i right ? The legal implications of second case(of commincation over sockets) are totally unclear to me !