How can I see a file as it was at a particular git commit?

Given a file foo.m, how can I get Git to show me the complete con开发者_JAVA百科tents of foo.m, as they were at some commit x?

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git checkout sha1_here  -- foo.m

or without checking the file out and just viewing it from the command line

git show sha1_here:path_to_file/foo.m