Eu bato à porta antes de entrar.

Yes. In Portuguese, subject pronouns are often left out because the verb ending already shows the person.

• Eu bato à porta antes de entrar.
• Bato à porta antes de entrar.

Both are correct. Including eu can add emphasis, contrast, or clarity. In many everyday situations, especially in European Portuguese, leaving it out sounds very natural.

Bato is the 1st person singular present tense of bater.

So:

• bater = to hit, beat, strike, knock
• bato = I hit / I beat / I knock

In this sentence, bater à porta is the normal expression for to knock on the door.

Because bater à porta is the usual idiomatic expression meaning to knock on the door.

Here, à is a contraction:

• a + a = à

So à porta literally looks like to the door, but in this expression it corresponds to English on the door.

Compare:

• bater à porta = to knock on the door
• estar à porta = to be at the door

You may sometimes hear bater na porta, especially in some varieties or contexts, but bater à porta is very standard and is especially natural in European Portuguese.

The accent in à is a grave accent, and it shows a contraction of two words:

• a (preposition)
• a (feminine singular definite article)

So:

• a + a porta → à porta

This is not just a pronunciation mark. It shows that two separate grammatical words have combined.

Because after antes, Portuguese normally uses the preposition de.

So:

• antes de entrar = before entering / before I enter

This is the standard structure.

Examples:

• Antes de sair, fecho a janela.
• Antes de comer, lavo as mãos.

So antes entrar would not be correct here.

Because after antes de, Portuguese uses the infinitive, not a conjugated form, when the subject is the same as the main clause.

Here the subject of both actions is the same person:

• Eu bato
• (eu) entrar

So the infinitive is used:

• Eu bato à porta antes de entrar.

If you used a conjugated verb, you would need a different structure, such as:

• Eu bato à porta antes de eu entrar.

That is grammatically possible, but less natural here because the subject is the same. The infinitive version is simpler and more common.

Yes, you could, but it is less natural in this sentence.

• antes de entrar is preferred when the subject is obvious and the same as in the main clause.
• antes de eu entrar is more likely when you want to stress the subject or make it especially clear.

For example:

• Eu bato à porta antes de entrar. = the normal version
• Eu bato à porta antes de eu entrar. = possible, but more explicit than necessary

If the subject changes, then the explicit subject becomes much more natural:

• Eu bato à porta antes de ela entrar.

Usually, this kind of sentence is understood as a habit or a general practice:

• Eu bato à porta antes de entrar. = I knock on the door before entering.

Portuguese present tense often covers what English calls the simple present for habits and routines.

Depending on context, it could also describe what someone is doing in a repeated or immediate sense, but the most natural reading here is habitual.

Yes. Porta is a feminine noun:

• a porta = the door

That is why the contraction is:

• a + a porta → à porta

If the noun were masculine singular, the contraction would be different:

• a + o = ao

For example:

• ao cinema
• ao médico

No. Bater has several meanings, and context matters.

Common meanings include:

• to hit
• to beat
• to strike
• to knock

Examples:

• bater na mesa = to hit the table
• bater os ovos = to beat the eggs
• bater à porta = to knock on the door

So in this sentence, the meaning to knock comes from the full expression bater à porta.

Not very naturally. A very literal breakdown would be something like:

• Eu = I
• bato = knock / hit
• à porta = at/to the door
• antes de entrar = before entering

But the natural English meaning is:

• I knock on the door before entering.

So it is better to learn bater à porta as a set expression rather than translating each word separately.

In European Portuguese, it is approximately:

• Eu bato à porta → something like eh-oo BAH-too ah POR-tuh

A few useful notes:

• eu often sounds closer to eh-oo or a compressed diphthong
• bato has stress on the first syllable: BA-to
• à is a short open a
• porta has stress on por

In fast European Portuguese speech, unstressed vowels are often reduced, so the rhythm may sound tighter than in a careful word-by-word pronunciation.

Without eu, yes:

• Bato à porta antes de entrar.

That is completely correct and very natural.

Changing the word order is possible in some cases, but the original order is the most straightforward. For example:

• Antes de entrar, bato à porta.

This also means the same thing and is very natural. It just puts more focus on the before entering part.