expression, godan verb (-tsu)
preserve life; keep alive
A somewhat formal or literary expression meaning to maintain one's life, often in difficult circumstances.
彼らはわずかな食料で命を保った。
They preserved their lives on meager food.
生き延びる is a more common, everyday verb meaning 'to survive' or 'to live through' a dangerous situation, while 命を保つ is a more formal phrase focusing on the act of maintaining life itself.
A compound phrase consisting of 命 (いのち, 'life') + を (object marker) + 保つ (たもつ, 'to keep, maintain'). The exact historical derivation is uncertain, but it follows a standard Japanese pattern of verb-object phrases.