[General] Countable nouns without the indefinite or with the definite article

[arjitsharma]

I would like to know the contexts or situation where countable nouns do not take any articles like in the following sentence:
Use knife when someone attacks.

I asked this question, because I have seen a countable noun is used without any article and sometimes with the articles.

 

[bubbha]

In the context of simple written instructions (such as on a vending machine or in a brief "how-to" guide), articles are often omitted.

Examples:

"Insert coin in slot."
"Hold knife in right hand."

 

[Tdol]

You'll also see this in things like headlines.

 

[arjitsharma]

So, can I omit the articles in day to day english?

 

[emsr2d2]

So (no comma here) can I omit the articles in day-to-day English?

See my corrections above.

 

[Tdol]

So, can I omit the articles in day to day english?

Are you speaking headlines? If not, choose ordinary grammar, not the conventions of compressing language to fit in a small space.