How to delete the first two characters of each row?

Ruby
1

how to delete the first two characters of each row?
i want to delete the first two characters of each row in file
/home/pt/test/mtp.txt

io=open("/home/pt/test/mtp.txt",“r”)
io1=open("/home/pt/test/mtpback.txt",“w”)
while line=io.gets
ioput=line.delete("/^…/")
io1.write(ioput)
end

when i open /home/pt/test/mtpback.txt,there is not what i want,where is
wrong?

2

Pen T. wrote:

how to delete the first two characters of each row?
i want to delete the first two characters of each row in file
/home/pt/test/mtp.txt

io=open("/home/pt/test/mtp.txt",“r”)
io1=open("/home/pt/test/mtpback.txt",“w”)
while line=io.gets
ioput=line.delete("/^…/")

You are trying to delete exactly the string of characters “/^…/”

You need to match against a regular expression instead. For example,

ioput=line.sub(/^..../, '')

(That will delete the first 4 characters in each line, but only if there
are 4 or more)

3

Pen T. wrote:

how to delete the first two characters of each row?
i want to delete the first two characters of each row in file
/home/pt/test/mtp.txt

io=open("/home/pt/test/mtp.txt",“r”)
io1=open("/home/pt/test/mtpback.txt",“w”)
while line=io.gets
ioput=line.delete("/^…/")
io1.write(ioput)
end

when i open /home/pt/test/mtpback.txt,there is not what i want,where is
wrong?

You could do

io=open("/home/pt/test/mtp.txt",“r”)
io1=open("/home/pt/test/mtpback.txt",“w”)
while line=io.gets
ioput=line[2…line.length] # extract substring without first two
characters
io1.write(ioput)
end

4

2010/4/13 Pen T. [email protected]:

end

when i open /home/pt/test/mtpback.txt,there is not what i want,where is
wrong?

At your favorite shell prompt:

$ cut -c 3- /home/pt/test/mtp.txt >| /home/pt/test/mtpback.txt

Kind regards

robert

5

Another option, utilizing Ruby’s mutable strings:

while line = io.gets
line.slice!(0, 2)
io1.write line
end

6

On Apr 13, 2010, at 4:17 AM, Pen T. wrote:

how to delete the first two characters of each row?
i want to delete the first two characters of each row in file
/home/pt/test/mtp.txt

io=open("/home/pt/test/mtp.txt",“r”)
io1=open("/home/pt/test/mtpback.txt",“w”)
while line=io.gets
ioput=line.delete("/^…/")

As Brian has mentioned, String#delete in your code is instructed to
remove the actual string starting with character ‘/’, not a regular
expression, as you might have meant. Also, most likely you want to
exclude end-of-lines from counting.

Another problem is that your files remain open, so you need to close
them at some point. I think you need something like this:

File.open("/home/pt/test/mtpback.txt", “w”) { |output|
File.open("/home/pt/test/mtp.txt", “r”) { |input|
input.each { |line|
output.puts line.chomp[2…-1].to_s
}
}
}

Gennady.

7

On Apr 13, 11:26 am, Tony A. [email protected] wrote:

Another option, utilizing Ruby’s mutable strings:

while line = io.gets
line.slice!(0, 2)
io1.write line
end

If you want to avoid temporary files:

Backup your file first, just in case, for testing purposes.

require ‘mmap’
m = Mmap.new(‘mtp.txt’, ‘rw’)
m.gsub!(/^…(.*)/, ‘\1’)
m.each{ |line| puts line }
m.unmap

Regards,

Dan

8

Robert K. wrote:

At your favorite shell prompt:

$ cut -c 3- /home/pt/test/mtp.txt >| /home/pt/test/mtpback.txt

Where is “>|” explained? Looks useful. I did “man bash”, and I can find
about three mentions of “>|” there, but it’s not explained.

(BTW, removing columns can be done in Vim too, it has a “visual block”
mode, which can be entered with Control-v.)

9

On 2010-04-14, Albert S. [email protected] wrote:

Robert K. wrote:

At your favorite shell prompt:

$ cut -c 3- /home/pt/test/mtp.txt >| /home/pt/test/mtpback.txt

Where is “>|” explained? Looks useful. I did “man bash”, and I can find
about three mentions of “>|” there, but it’s not explained.

   If  the  redirection  operator  is  >,  and  the  noclobber
   option to the set builtin has been enabled, the redirection
   will fail if the file whose name results from the expansion
   of  word exists  and is a regular file.  If the redirection
   operator is >|, or the redirection operator is > and the
   noclobber option to the set builtin command is not enabled,
   the  redirection  is attempted even if the file named by
   word exists.

-s

10

On 14.04.2010 03:06, Albert S. wrote:

Robert K. wrote:

At your favorite shell prompt:

$ cut -c 3- /home/pt/test/mtp.txt>| /home/pt/test/mtpback.txt

Where is “>|” explained? Looks useful. I did “man bash”, and I can find
about three mentions of “>|” there, but it’s not explained.

This is even part of the POSIX standard. I don’t have the link handy
and I believe you must register with them but reading and downloading
the standard is free.

(BTW, removing columns can be done in Vim too, it has a “visual block”
mode, which can be entered with Control-v.)

Cool, thanks for the hint! In vi(m) I would probably have used
“:%s/^…//”. :slight_smile:

Kind regards

robert