<!-- GENERATED by docs/sphinx/bin/02-reference from Digest/SHA.rs (xs_new). Do not edit. -->

```{index} single: new; Digest::SHA function
```
```{index} single: Digest::SHA::new; Perl function
```

# new

Construct or reinitialise a `Digest::SHA` object.

The primary object constructor. Works as both a class method
(`Digest::SHA->new(256)`) and an instance method
(`$sha->new(512)`), and accepts the algorithm in any of the shapes
`Digest::SHA` recognises: an integer like `256`, a string like
`"SHA-256"`, `"sha256"`, or `"512/224"`. When called without an
algorithm argument it defaults to SHA-1.

As an instance method, `new` reuses the existing object: supplying a
new algorithm resets state and switches to that algorithm; omitting it
simply rewinds the state (same as `reset`).

## Synopsis

```perl
my $sha = Digest::SHA->new(256);
my $sha = Digest::SHA->new("SHA-512/256");
$sha->new;                       # rewind, keep algorithm
$sha->new(384);                  # rewind, switch to SHA-384
```

## What you get back

A blessed `Digest::SHA` object, or `undef` when the algorithm argument
cannot be parsed as a supported algorithm.

## Examples

```perl
my $sha = Digest::SHA->new("sha256");
$sha->add("The quick brown fox ", "jumps over the lazy dog");
print $sha->hexdigest;

## d7a8fbb307d7809469ca9abcb0082e4f8d5651e46d3cdb762d02d0bf37c9e592

```

```perl
my $sha = Digest::SHA->new(512);
$sha->add_bits("01011010");       # hash exactly 8 bits
```

```perl
my $sha = Digest::SHA->new(256);
$sha->add("first");
$sha->new(512);                   # rewind and switch
$sha->add("second");              # now hashing with SHA-512
```

## Edge cases

- No algorithm argument defaults to SHA-1.
- An unparseable algorithm returns `undef`; check the return value
  before chaining `->add`.
- Called on an existing object, `new` mutates that object in place and
  returns it — it does not allocate a second context.

## Differences from upstream

Fully compatible with upstream `Digest::SHA` {{ upstream.Digest_SHA }}.

## See also

- `reset` — explicit rewind, same semantics as the no-argument instance form.
- `clone` — copy the current state into a fresh object.
- `newSHA` — lower-level XS constructor taking an integer algorithm code.