A readline + -e oddity: readline opens files even with -e --- need "readline STDIN" to read from console

(This is my first meditation. I am posting in hopes it will help someone down the line! I can't find another node about this, but that doesn't mean there isn't one :) .)

I needed to run a program and then wait for the user to hit Enter. I tried this:

$ perl -e 'system(@ARGV); readline' echo foo
foo
Can't open echo: No such file or directory at -e line 1.
Can't open foo: No such file or directory at -e line 1.
[download]

Not what I expected!

After all, perlrun says that:

If -e is given, Perl will not look for a filename in the argument list.

What I was missing is that readline does look at the argument list. Readline:

reads ...from *ARGV if EXPR is not provided

So what I needed was to expressly read from STDIN to get my keypress:

                                 # vvvvv
$ perl -e 'system(@ARGV); readline STDIN' echo foo
foo
    (<=== waited here for me to press Enter)
[download]

Comment on A readline + -e oddity: readline opens files even with -e --- need "readline STDIN" to read from console Select or Download Code

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Re: A readline + -e oddity: readline opens files even with -e --- need "readline STDIN" to read from console by choroba (Cardinal) on Nov 30, 2020 at 16:47 UTC
Another possibility would be to remove the consumed arguments from @ARGV: `perl -e 'system splice @ARGV; readline' echo foo` [download] `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]
Re: A readline + -e oddity: readline opens files even with -e --- need "readline STDIN" to read from console by haukex (Archbishop) on Nov 30, 2020 at 16:50 UTC
You might be interested in what Perl::Critic::Policy::InputOutput::ProhibitExplicitStdin and the corresponding part of PBP has to say about it. Also, you might want to consider checking via IO::Interactive to see if the terminal is actually interactive. `use warnings; use strict; use IO::Interactive 'is_interactive'; use Term::ReadLine; print "Hello, World!\n"; if ( is_interactive() ) { print "Press Enter to continue...\n"; Term::ReadLine->new("")->readline(""); } else { warn "Noninteractive, continuing...\n" }` [download] This will prompt the user to press enter if connected to a terminal, but if the script is used in a non-interactive environment (simple example: `perl script.pl \| cat`), it won't. See also other prompting alternatives.	[reply] [d/l] [select]
Re: A readline + -e oddity: readline opens files even with -e --- need "readline STDIN" to read from console (perl -MO=Deparse) by Anonymous Monk on Dec 01, 2020 at 00:27 UTC
:) Basic debugging checklist `$ perl -MO=Deparse -e " system(@ARGV); readline " echo foo system @ARGV; <ARGV>; -e syntax OK` [download]	[reply] [d/l]
Re: A readline + -e oddity: readline opens files even with -e --- need "readline STDIN" to read from console by Anonymous Monk on Nov 30, 2020 at 19:43 UTC
Why is this a "Meditation?" Sure looks to me like someone is "Seeking Perl Wisdom" ...	[reply]
Re^2: A readline + -e oddity: readline opens files even with -e --- need "readline STDIN" to read from console by cxw (Scribe) on Dec 01, 2020 at 14:13 UTC
Because I already fixed my problem ;) .	[reply]


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