---
name: select
status: documented
runtime: pp
source: src/runtime/pp/fileio.rs
---
```{index} single: select; Perl built-in (pp runtime)
```

# select

## Synopsis

```perl
$prev = select($fh);                                # 1-arg form
$nfound = select($rbits, $wbits, $ebits, $timeout); # 4-arg form
```

## Description

Sets the default output filehandle or performs I/O multiplexing.

**1-argument form**: Sets the default output filehandle (used by
`print` and `write` when no explicit handle is given) and returns the
previously selected handle. With no arguments, returns the current
default output handle name without changing it.

**4-argument form**: Wraps the POSIX `select(2)` system call. Waits
for I/O readiness on the file descriptors encoded in the bit vectors
RBITS (readable), WBITS (writable), and EBITS (exceptional). TIMEOUT
is in seconds (may be fractional). Returns the number of ready
descriptors, or -1 on error.

## See also

print, IO::Select, fileno