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```{index} single: sigprocmask; POSIX function
```
```{index} single: POSIX::sigprocmask; Perl function
```

# sigprocmask

Change, query, or both the set of signals blocked for this process.

## Synopsis

```perl
use POSIX qw(sigprocmask SIG_BLOCK SIG_UNBLOCK SIG_SETMASK);
my $mask = POSIX::SigSet->new(SIGINT);
sigprocmask(SIG_BLOCK, $mask);
```

## What you get back

`"0 but true"` on success, `undef` on failure. When `$oldsigset`
is supplied, it is filled with the mask in effect before the call.

## Edge cases

- Passing a non-`POSIX::SigSet` reference for either set croaks
  with `sigset is not of type POSIX::SigSet` /
  `oldsigset is not of type POSIX::SigSet`.

## Differences from upstream

Fully compatible with upstream POSIX.

## See also

- `sigpending`, `sigsuspend`, `sigaction` — the rest of the
  POSIX signal API.