Fix dynamic string usage as safe input
Fix dynamic string usage as safe input

Test Plan: Copied the code in a script, changed `phutil_passthru()` to `echo csprintf()` and ran it.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4805

aik099/arcanist,wharris/arcanist,fivestars/arcanist,sneakpeeq/arcanist,jra3/arcanist,hach-que/arcanist,haskell-infra/arcanist,kevinseelbach/arcanist,r4nt/arcanist,Khan/arcanist,wxstars/arcanist,wxstars/arcanist,sneakpeeq/arcanist,calblueprint/arcanist,chundongwang/arcanist,alexmv/arcanist,jra3/arcanist,zhihu/arcanist,sneakpeeq/arcanist,PageUpPeopleOrg/arcanist-patches,folsom-labs/arcanist,folsom-labs/arcanist,phacility/arcanist,codelabs-ch/arcanist,aik099/arcanist,julkiewicz/arcanist,eSpark/arcanist,memsql/arcanist,uber/arcanist,wikimedia/phabricator-arcanist,aik099/arcanist,calblueprint/arcanist,Khan/arcanist,haskell-infra/arcanist,Symplicity/arcanist,haskell-infra/arcanist,alexmv/arcanist,zhihu/arcanist,wikimedia/phabricator-arcanist,alexmv/arcanist,PageUpPeopleOrg/arcanist-patches,aik099/arcanist,r4nt/arcanist,calblueprint/arcanist,codelabs-ch/arcanist,memsql/arcanist,eSpark/arcanist,folsom-labs/arcanist,KieranHayes/arcanist,zhihu/arcanist,r4nt/arcanist,memsql/arcanist,coursera/arcanist,uber/arcanist,haskell-infra/arcanist,julkiewicz/arcanist,codelabs-ch/arcanist,Symplicity/arcanist,Symplicity/arcanist,kevinseelbach/arcanist,KieranHayes/arcanist,Khan/arcanist,julkiewicz/arcanist,chundongwang/arcanist,zhihu/arcanist,wharris/arcanist,folsom-labs/arcanist,sneakpeeq/arcanist,wxstars/arcanist,wikimedia/phabricator-arcanist,coursera/arcanist,dguo-coursera/arcanist,chundongwang/arcanist,coursera/arcanist,memsql/arcanist,chundongwang/arcanist,r4nt/arcanist,kevinseelbach/arcanist,dguo-coursera/arcanist,kevinseelbach/arcanist,alexmv/arcanist,Symplicity/arcanist,jra3/arcanist,calblueprint/arcanist,codelabs-ch/arcanist,KieranHayes/arcanist,Khan/arcanist,PageUpPeopleOrg/arcanist-patches,KieranHayes/arcanist,hach-que/arcanist,PageUpPeopleOrg/arcanist-patches,uber/arcanist,phacility/arcanist,hach-que/arcanist,eSpark/arcanist,wikimedia/phabricator-arcanist,wharris/arcanist,dguo-coursera/arcanist,jra3/arcanist,codelabs-ch/arcanist,fivestars/arcanist,uber/arcanist,phacility/arcanist,dguo-coursera/arcanist,wharris/arcanist,julkiewicz/arcanist,fivestars/arcanist,wxstars/arcanist,hach-que/arcanist,coursera/arcanist,eSpark/arcanist,fivestars/arcanist,phacility/arcanist,phacility/arcanist