how do I "initialize" $

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

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Re: how do I "initialize" $_ by AnomalousMonk (Archbishop) on Oct 11, 2018 at 04:51 UTC
The default scalar `$_` (see perlvar) is assigned to in some cases, but not all; you've chosen one of the "not all" cases. A `while`-loop like `while (<FILEHANDLE>) { print; }` [download] is really `while (defined($_ = <FILEHANDLE>)) { print $_; }` [download] and likewise `for (<FILEHANDLE>) { print; }` [download] is `for $_ (<FILEHANDLE>) { print $_; }` [download] (Note that the `while`-loop will read and print the filehandle line-by-line, but the `for`-loop will read all lines of the file at once (could be a lotta lines!) and then print the lines one-by-one.) See perlsyn. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^2: how do I "initialize" $_ by Anonymous Monk on Oct 11, 2018 at 06:46 UTC
Thanks. I knew other ways of reading the data (assigning it a variable or using a loop), but I didn't know why the "automatic" assignment didn't work in this case, and you explained that the best.	[reply]
Re^3: how do I "initialize" $_ by Marshall (Canon) on Oct 12, 2018 at 19:47 UTC
Yes, BTW, your code: `<FILEHANDLE>;` just causes the first line to be discarded since it is not assigned to anything. I guess as another point, with strict; and warnings; active, when reading from the predefined DATA file handle, you will get a warning if you don't have the `while (defined (my $line =<DATA>)){}` syntax, that is because a line with just "0" could evaluate to "false". On "real file handles" the action is a bit different - Perl is very good at "doing what I meant" and the defined() is implicit. Perl is a huge language and abounds with little fine differences.	[reply] [d/l] [select]
Re^4: how do I "initialize" $_ by haukex (Archbishop) on Oct 13, 2018 at 08:47 UTC
Re^5: how do I "initialize" $_ by Marshall (Canon) on Nov 01, 2018 at 06:57 UTC
Re^4: how do I "initialize" $_ (updated) by AnomalousMonk (Archbishop) on Oct 13, 2018 at 02:10 UTC
Re^5: how do I "initialize" $_ by Marshall (Canon) on Oct 13, 2018 at 04:21 UTC
Some notes below your chosen depth have not been shown here
Re: how do I "initialize" $_ by tybalt89 (Monsignor) on Oct 11, 2018 at 03:22 UTC
`$_ = <FILEHANDLE>;` [download]	[reply] [d/l]
Re: how do I "initialize" $_ by Marshall (Canon) on Oct 11, 2018 at 04:43 UTC
`open (FILEHANDLE, '<', 'some.file') or die "Can't open some.file for r +eading.\n"; while (<FILEHANDLE>) { print; }` [download] Update: In general, I almost never have a statement like `$_ = $var`. I'm sure that I've done that, but in very,very special situations. To read the first line: `my $first = <FILEHANDLE>;` [download]	[reply] [d/l] [select]
Re: how do I "initialize" $_ by holli (Abbot) on Oct 11, 2018 at 17:31 UTC
Whatever learning material you use - if it teaches you to still use bareword FILEHANDLES in 2018 - it is outdated. What are you learning from? holli You can lead your users to water, but alas, you cannot drown them.	[reply] [d/l]