The usual phrase is "get in line", no "a".
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AnonymousTell the soldiers to ...... get in line.
CalifJim... get in line.OR... form a line.Thanks a lot, CJ.
CalifJimThe article often goes missing after a preposition when the prepositional phrase has a special idiomatic meaning.So it is because of a special idiomatic meaning the article is not used, which is seen as another exception (in which a noun does not need a de