The country’s main industry federation said the business community welcomed the result. So have most newspapers, one calling it “a day of hope for all Egyptians”.
Source: Euronews.com, Sisi Secures Crushing Win in Egypt Presidential Vote
Is this grammatical? Is it an expression? What does it mean?
The country’s main industry federation said the business community welcomed the result.
So have most newspapers…
Here, so is a pro-form. It's used instead of repeating an earlier verb phrase ("welcomed the result"), and it adds the meaning "too". It also triggers Subject-Auxiliary Inversion.
To paraphrase it, we can remove so, undo the inversion, put in the missing constituent, and add too to preserve the meaning:
Most newspapers have welcomed the result, too…
Now we've paraphrased your sentence. (Well, the first half, anyway.)
