Chop problems

ruby-talk
1

Hello, I'm new here, also fairly new to ruby, but I already have some very usfull scripts written with it.

But a problem I have over and over is that the 'chop' doesn't always work (for me) when dealing with files.

An example, the file '/tmp/dirtree' is the result of a class that traverses the directory tree, the lines are written using,

f.print "#{filename}\n"
(but I've also tried others writing methods)

Then next would be the class to read from that file.

DIRTREE='/tmp/dirtree'
IO.foreach(DIRTREE) { |@x|
         @x.chop
         print "Thisdir = #{@x}/*"
}

The output from print gives,

Thisdir = /home/whatever
/*

So chop hasn't removed the newline.

Do you use a definitive combination of file write and read that will always work, or is there another trick I don't know about yet.

PS: I' on UNIX/Linux.

Thankyou

2

"BearItAll" <spam@rassler.co.uk> schrieb im Newsbeitrag
news:1107426590.1467.0@eunomia.uk.clara.net...

Hello, I'm new here, also fairly new to ruby, but I already have some
very usfull scripts written with it.

But a problem I have over and over is that the 'chop' doesn't always
work (for me) when dealing with files.

An example, the file '/tmp/dirtree' is the result of a class that
traverses the directory tree, the lines are written using,

f.print "#{filename}\n"
(but I've also tried others writing methods)

"f.puts filename" does the same more efficiently.

Then next would be the class to read from that file.

DIRTREE='/tmp/dirtree'
IO.foreach(DIRTREE) { |@x|
         @x.chop
         print "Thisdir = #{@x}/*"
}

The output from print gives,

Thisdir = /home/whatever
/*

So chop hasn't removed the newline.

You want chop!() because you want to modify @x. chop() just returns a
copy of the string with the last char removed. But even better use
chomp!(), because chop!() and chop() always remove the last char -
regardless what it is:

s="abcde\n"

=> "abcde\n"

s.chop!

=> "abcde"

s.chop!

=> "abcd"

s.chop!

=> "abc"

s.chop!

=> "ab"

s.chop!

=> "a"

s.chop!

=> ""

s.chop!

=> nil

Do you use a definitive combination of file write and read that will
always work, or is there another trick I don't know about yet.

Kind regards

    robert

3

Robert Klemme wrote:

"BearItAll" <spam@rassler.co.uk> schrieb im Newsbeitrag
news:1107426590.1467.0@eunomia.uk.clara.net...

Hello, I'm new here, also fairly new to ruby, but I already have some
very usfull scripts written with it.

But a problem I have over and over is that the 'chop' doesn't always
work (for me) when dealing with files.

An example, the file '/tmp/dirtree' is the result of a class that
traverses the directory tree, the lines are written using,

f.print "#{filename}\n"
(but I've also tried others writing methods)

"f.puts filename" does the same more efficiently.

Then next would be the class to read from that file.

DIRTREE='/tmp/dirtree'
IO.foreach(DIRTREE) { |@x|
        @x.chop
        print "Thisdir = #{@x}/*"
}

The output from print gives,

Thisdir = /home/whatever
/*

So chop hasn't removed the newline.

You want chop!() because you want to modify @x. chop() just returns a
copy of the string with the last char removed. But even better use
chomp!(), because chop!() and chop() always remove the last char -
regardless what it is:

s="abcde\n"

=> "abcde\n"

s.chop!

=> "abcde"

s.chop!

=> "abcd"

s.chop!

=> "abc"

s.chop!

=> "ab"

s.chop!

=> "a"

s.chop!

=> ""

s.chop!

=> nil

Do you use a definitive combination of file write and read that will
always work, or is there another trick I don't know about yet.

Kind regards

    robert

Thankyou, I love you loads.

Strange really how I read that "Returns a new string..." a billion times, without actually noticing what it said.

But then I'm the same with tax return forms.

So as a reward you are welcome to join me in a all expenses paid round the world holiday on my yaght. it's about 3 foot long and 2 foot wide with one oar each. Let me know when your avaiable.

4

Robert Klemme schrieb:

"BearItAll" <spam@rassler.co.uk> schrieb im Newsbeitrag
news:1107432176.47652.0@demeter.uk.clara.net...

So as a reward you are welcome to join me in a all expenses paid round
the world holiday on my yaght. it's about 3 foot long and 2 foot wide
with one oar each. Let me know when your avaiable.

Lemmesee, I think, before I can join this invitation I'll have to undergo
some shrinking - otherwise there'll be hardly enough space on your
"ship"...

Should be easy:

   robert.chop!

Regards,
Pit

5

BearItAll, 3/2/2005 09:05:

Strange really how I read that "Returns a new string..." a billion times, without actually noticing what it said.

@x = @x.chop
is the same as
@x.chop!

@x.chop return a new string you can assing to a variable you want to.

6

"Pit Capitain" <pit@capitain.de> schrieb im Newsbeitrag
news:42021CFA.7000006@capitain.de...

Robert Klemme schrieb:
> "BearItAll" <spam@rassler.co.uk> schrieb im Newsbeitrag
> news:1107432176.47652.0@demeter.uk.clara.net...
>>So as a reward you are welcome to join me in a all expenses paid round
>>the world holiday on my yaght. it's about 3 foot long and 2 foot wide
>>with one oar each. Let me know when your avaiable.
>
> Lemmesee, I think, before I can join this invitation I'll have to

undergo

> some shrinking - otherwise there'll be hardly enough space on your
> "ship"...

Should be easy:

   robert.chop!

Dar, didn' thin tha i wa s eas.

Cheer

    rober

7

"Caio Tiago Oliveira" <caiot1@ibest.com.br> schrieb im Newsbeitrag
news:42025196.2050502@ibest.com.br...

BearItAll, 3/2/2005 09:05:

> Strange really how I read that "Returns a new string..." a billion
> times, without actually noticing what it said.

@x = @x.chop
is the same as
@x.chop!

No, it is not. In many applications this might be equivalent but it's not
the same. @x.chop! does not create a new instance, i.e. whoever holds a
reference to that instance sees the change. @x=@x.chop creates a new
instance so everybody else referencing the old value of @x sees no change.
Also, it makes a difference when you consider #freeze:

s = "abcd"

=> "abcd"

s.freeze

=> "abcd"

s.chop!

TypeError: can't modify frozen string
        from (irb):3:in `chop!'
        from (irb):3

s = s.chop

=> "abc"

Also, it makes a difference performance wise. The first form is usually
slower since a new instance has to be created.

@x.chop return a new string you can assing to a variable you want to.

Yes.

Kind regards

    robert