West Yorkshire Police said a woman, thought to be in her 20s, went into the shop on Clough Lane, Mixenden, Halifax on Thursday night brandishing a knife.
She demanded money from the 53-year-old man and when he refused a struggle began. During the attack he was knifed several times.
The woman fled the shop with a "significant" amount of cash. Police have been studying CCTV footage.
The 53-year-old man was taken to Huddersfield Royal Infirmary, where he is said to be in a stable condition.
Det Insp Ashley Hewitt of Calderdale CID said: "We think the woman headed in the direction of Hunter Hill Road and the victim thinks he heard a car but he did not see one, so it is not clear whether she left on foot or by car.
"Inquiries are ongoing and we are looking at CCTV footage from the area.
"The woman is described as white, 5ft 7in (1.70m), of chubby build with a chubby face, and possibly had a piercing in her top lip.
"She was wearing a black shell suit with a hood."
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