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virusso80

Member

From: Italy

Registered: 2007-03-09

Posts: 325

How to use shell commands inside a C program

Hi all, I hope to find someone that can help me.

I'm struggling in using the command base64, which encodes a file to another one

more in details, the following command works

echo VGhlIExpbnV4IEpvdXJuYWwK | base64 -d
and gives the proper result (The Linux Journal)

Is there a way to get the result into a C variable (i.e char*)?

PS i know that the method "system("type here the shell command") executes the command, but output is not recoverable...i mean, i don't know how.

Thanks

Last edited by virusso80 (2010-05-25 18:13:37)

ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 20,334

Re: How to use shell commands inside a C program

man 3 exec
man fork
man pipe

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fsckd

Forum Fellow

Registered: 2009-06-15

Posts: 4,173

Re: How to use shell commands inside a C program

I think popen is what you are looking for.

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n0dix

Member

Registered: 2009-09-22

Posts: 956

Re: How to use shell commands inside a C program

i second popen.

Last edited by n0dix (2010-05-25 18:56:37)

kazuo

Member

From: São Paulo/Brazil

Registered: 2008-03-18

Posts: 413

Website

Re: How to use shell commands inside a C program

But, you probably dont what to use it (popen), I think this can really slow down you program, I recommend that you implement a base64 dec/enc in C for example http://base64.sourceforge.net/b64.c

Trent

Member

From: Baltimore, MD (US)

Registered: 2009-04-16

Posts: 990

Re: How to use shell commands inside a C program

Yes, don't use popen if you can avoid it.  For one thing it is slower, and for another it is less portable.  Write your own conversion algorithm (it's relatively short), or use someone else's.  Googling "base64 C library" brings up libb64 and a smattering of others.

Daenyth

Forum Fellow

From: Boston, MA

Registered: 2008-02-24

Posts: 1,244

Re: How to use shell commands inside a C program

You should try to use a native library where possible

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kazuo

Member

From: São Paulo/Brazil

Registered: 2008-03-18

Posts: 413

Website

Re: How to use shell commands inside a C program

And probably some library already provide base64, in my mind come openssl (its is a core package). For example google give me this http://www.ioncannon.net/programming/34 … d-openssl/ and http://www.mail-archive.com/openssl-use … 58722.html