readline - perldoc.perl.org

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# readline

Perl 5 version 12.2 documentation
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# readline

Perl functions A-Z | Perl functions by category | The 'perlfunc' manpage

- readline EXPR
- readline

  Reads from the filehandle whose typeglob is contained in EXPR (or from *ARGV if EXPR is not provided). In scalar context, each call reads and returns the next line until end-of-file is reached, whereupon the subsequent call returns `undef`. In list context, reads until end-of-file is reached and returns a list of lines. Note that the notion of "line" used here is whatever you may have defined with `$/` or `$INPUT_RECORD_SEPARATOR` ). See $/ in perlvar.

  When `$/` is set to `undef`, when `readline` is in scalar context (i.e., file slurp mode), and when an empty file is read, it returns `''` the first time, followed by `undef` subsequently.

  This is the internal function implementing the `<EXPR>` operator, but you can use it directly. The `<EXPR>` operator is discussed in more detail in I/O Operators in perlop.

          $line = <STDIN>;    $line = readline(*STDIN);    # same thing

  If `readline` encounters an operating system error, `$!` will be set with the corresponding error message. It can be helpful to check `$!` when you are reading from filehandles you don't trust, such as a tty or a socket. The following example uses the operator form of `readline` and dies if the result is not defined.

          while ( ! eof($fh) ) {        defined( $_ = <$fh> ) or die "readline failed: $!";        ...    }

  Note that you have can't handle `readline` errors that way with the `ARGV` filehandle. In that case, you have to open each element of `@ARGV` yourself since `eof` handles `ARGV` differently.

          foreach my $arg (@ARGV) {        open(my $fh, $arg) or warn "Can't open $arg: $!";        while ( ! eof($fh) ) {            defined( $_ = <$fh> )                or die "readline failed for $arg: $!";            ...        }    }