From: Eric Christopherson <echristopherson@...>
Date: 2013-06-14T08:14:38+09:00
Subject: Re: Unexpected output piping to ruby -pe ''

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On Thu, Jun 13, 2013 at 4:49 PM, Greg Ferguson <lists@ruby-forum.com> wrote:

> How come Ruby outputs the incoming piped text when there is no code to
> evaluate:
>
>     echo foo | ruby -pe ''
>
> outputs: "foo"
>
> Without "-p" there's no output, which I'd expect. Without '' there's an
> error, which I'd expect when using the "-e" flag.
>
> Is there a silent return value of the incoming text that "-p" is then
> printing?
>

Not a return value.

From `ruby --help`:
  -n              assume 'while gets(); ... end' loop around your script
  -p              assume loop like -n but print line also like sed

So it creates a loop around the (empty) expression; the loop keeps getting
the next line from stdin until EOF; and it prints the line. (Actually I
believe the line printed is the special variable $_, which gets writes to
implicitly. In an actual useful one-liner you would probably filter out
certain lines and/or run sub or gsub -- when invoked as Kernel methods,
these  also implicitly write to $_.)

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<div dir=3D"ltr">On Thu, Jun 13, 2013 at 4:49 PM, Greg Ferguson <span dir=
=3D"ltr">&lt;<a href=3D"mailto:lists@ruby-forum.com" target=3D"_blank">list=
s@ruby-forum.com</a>&gt;</span> wrote:<br><div class=3D"gmail_extra"><div c=
lass=3D"gmail_quote">

<blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-=
left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;p=
adding-left:1ex">How come Ruby outputs the incoming piped text when there i=
s no code to<br>


evaluate:<br>
<br>
=C2=A0 =C2=A0 echo foo | ruby -pe &#39;&#39;<br>
<br>
outputs: &quot;foo&quot;<br>
<br>
Without &quot;-p&quot; there&#39;s no output, which I&#39;d expect. Without=
 &#39;&#39; there&#39;s an<br>
error, which I&#39;d expect when using the &quot;-e&quot; flag.<br>
<br>
Is there a silent return value of the incoming text that &quot;-p&quot; is =
then<br>
printing?<br></blockquote><div><br></div><div style>Not a return value.</di=
v><div style><br></div><div style>From `ruby --help`:</div><div style>=C2=
=A0 -n =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0assume &#39;while ge=
ts(); ... end&#39; loop around your script</div>

<div style>=C2=A0 -p =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0assume=
 loop like -n but print line also like sed<br></div><div style><br></div><d=
iv style>So it creates a loop around the (empty) expression; the loop keeps=
 getting the next line from stdin until EOF; and it prints the line. (Actua=
lly I believe the line printed is the special variable $_, which gets write=
s to implicitly. In an actual useful one-liner you would probably filter ou=
t certain lines and/or run sub or gsub -- when invoked as Kernel methods, t=
hese =C2=A0also implicitly write to $_.)</div>

</div></div></div>

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