[R] It is possible to use a Shell command inside a R script?

[Ronaldo Reis Junior]

Hi,

It is possible to use a shell command inside a R script?

I'm write a R script and I like to put somes shell commands inside to R. 
Somethink like: convert fig01.png fig01.xpm or sed ..., etc.

It is possible? How?

Thanks
Ronaldo
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