This question is kinda simple (don't be so harsh with me), but I can't get a code-beautiful solution. I have the following code:
ARGF.each_line do |line|
arguments = line.split(',')
arguments.each do |task|
puts "#{task} result"
end
end
It simply read from the standard input numbers. I use it this way:
echo "1,2,3" | ruby prog.rb
The output desired is
1 result
2 result
3 result
But the actual output is
1 result
2 result
3
result
It seems like there's a newline character introduced. I'm skipping something?
Each line ends in a newline character, so splitting on commas in your example means that the last token is 3\n. Printing this prints 3 and then a newline.
Try using
arguments = line.chomp.split(',')
To remove the trailing newlines before splitting.
Your stdin input includes a trailing newline character. Try calling line.chomp! as the first instruction in your each_line block.
Related
I have a following file:
old_file
new_file
Some string.
end
Text in the middle that is not supposed to go to any of files.
new_file
Another text.
end
How using regex can I create two files with the following content:
file1
new_file
Some string.
end
file2
new_file
Another text.
end
How can I get information which is between keywords 'new_file' and 'end' to write it to the file?
If your files are not that large, you can read them in as a string, (use File.read(file_name)), and then run the following regex:
file_contents.scan(/^new_file$.*?^end$/m).select { |block| WRITE_TO_FILE_CODE_HERE }
See the regex demo
The ^new_file$.*?^end$ regex matches new_file that is a whole line content, then 0+ any characters as few as possible (incl. a newline as /m modifier is used), and then end (a whole line).
Else, you may adapt this answer here as
printing = false
File.open(my_file).each_line do |line|
printing = true if line =~ /^new_file$/
puts line if printing
printing = false if line =~ /^end$/
end
Open the file when the starting line is found, write to it where puts line is in the example above, and close when printing false occurs.
You can also read the file chunk by chunk by changing what constitutes a "line" in ruby:
File.open("file1.txt", "w") do |file1|
File.open("file2.txt", "w") do |file2|
enum = IO.foreach("old_file.txt", sep="\n\n")
file1.puts enum.next.strip
enum.next #discard
file2.puts enum.next.strip
end #automatically closes file2
end #automatically closes file1
By designating the separator as "\n\n" ruby will read all the characters up to and including two consecutive newlines--and return that as a "line".
If that kind of format is fixed, then you may try this (new_file\n.*\nend)
Updated description to be clearer.
Say I have a file and it has these lines in it.
one
two
three
five
How do I add a line that says "four" after the line that says "three" so my file now looks like this?
one
two
three
four
five
Assuming you want to do this with the FileEdit class.
Chef::Util::FileEdit.new('/path/to/file').insert_line_after_match(/three/, 'four')
Here is the example ruby block for inserting 2 new line after match:
ruby_block "insert_lines" do
block do
file = Chef::Util::FileEdit.new("/path/of/file")
file.insert_line_after_match("three", "four")
file.insert_line_after_match("four", "five")
file.write_file
end
end
insert_line_after_match searches for the regex/string and it will insert the value in after the match.
The following Ruby script should do what you want quite nicely:
# insert_line.rb
# run with command "ruby insert_line.rb myinputfile.txt", where you
# replace "myinputfile.txt" with the actual name of your input file
$-i = ".orig"
ARGF.each do |line|
puts line
puts "four" if line =~ /^three$/
end
The $-i = ".orig" line makes the script appear to edit the named input file in-place and make a backup copy with ".orig" appended to the name. In reality it reads from the specified file and writes output to a temp file, and on success renames both the original input file (to have the specified suffix) and the temp file (to have the original name).
This particular implementation writes "four" after finding the "three" line, but it would be trivial to alter the pattern being matched, make it count-based, or have it write before some identified line rather than after.
This is an in memory solution. It looks for complete lines rather than doing a string regex search...
def add_after_line_in_memory path, findline, newline
lines = File.readlines(path)
if i = lines.index(findline.to_s+$/)
lines.insert(i+1, newline.to_s+$/)
File.open(path, 'wb') { |file| file.write(lines.join) }
end
end
add_after_line_in_memory 'onetwothreefive.txt', 'three', 'four'
An AWK Solution
While you could do this in Ruby, it's actually trivial to do this in AWK. For example:
# Use the line number to choose the insertion point.
$ awk 'NR == 4 {print "four"}; {print}' lines
one
two
three
four
five
# Use a regex to prepend your string to the matched line.
$ awk '/five/ {print "four"}; {print}' lines
one
two
three
four
five
How would i put line breaks in between lines like this:
print "Hi"
print "Hi"
Because it would just output this:
HiHi
Use puts since it will automatically add a newline for you:
puts "Hi"
puts "Hi"
If you want to make an explicit newline character then you'll need to know what kind of system(s) on which your program will run:
print "Hi\n" # For UNIX-like systems including Mac OS X.
print "Hi\r\n" # For Windows.
Use line break character:
print "Hi\n"
print "Hi"
puts "\n" works also on Win/Ruby ruby 2.4.2p198
and even "\n"*4 for multiplication of new rows (by 4)
You can create a space by adding a string with only a space in it between the 2 other strings. For example:
print "Hi" + " " + "Hi"
You could avoid the two print statements and instead only use one line.
print "Hi\r\nHi"
Or if you want to use two lines then
print "Hi\r\n"
print "Hi"
cud any body tell me how this expression works
output = "#{output.gsub(/grep .*$/,'')}"
before that opearation value of ouptput is
"df -h | grep /mnt/nand\r\n/dev/mtdblock4 248.5M 130.7M 117.8M 53% /mnt/nand\r\n"
but after opeartion it comes
"df -h | \n/dev/mtdblock4 248.5M 248.5M 130.7M 117.8M 53% /mnt/nand\r\n "
plzz help me
Your expression is equivalent to:
output.gsub!(/grep .*$/,'')
which is much easier to read.
The . in the regular expression matches all characters except newline by default. So, in the string provided, it matches "grep /mnt/nand", and will substitute a blank string for that. The result is the provided string, without the matched substring.
Here is a simpler example:
"hello\n\n\nworld".gsub(/hello.*$/,'') => "\n\n\nworld"
In both your provided regex, and the example above, the $ is not necessary. It is used as an anchor to match the end of a line, but since the pattern immediately before it (.*) matches everything up to a newline, it is redundant (but does not cause harm).
Since gsub returns a string, your first line is exactly the same as
output = output.gsub(/grep .*$/, '')
which takes the string and removes any occurance of the regexp pattern
/grep .*$/
i.e. all parts of the string that start with 'grep ' until the end of the string or a line break.
There's a good regexp tester/reference here. This one matches the word "grep", then a space, then any number of characters until the next line-break (\r or \n). "." by itself means any character, and ".*" together means any number of them, as many as possible. "$" means the end of a line.
For the '$', see here http://www.regular-expressions.info/reference.html
".*$" means "take every character from the end of the string" ; but the parser will interpret the "\n" as the end of a line, so it stops here.
I have a script written in ruby. I need to remove any duplicate newlines (e.g.)
\n
\n
\n
to
\n
My current attempt worked (or rather not) using
str.gsub!(/\n\n/, "\n")
Which gave me no change to the output. What am I doing wrong?
This works for me:
#!/usr/bin/ruby
$s = "foo\n\n\nbar\nbaz\n\n\nquux";
puts $s
$s.gsub!(/[\n]+/, "\n");
puts $s
Use the more idiomatic String#squeeze instead of gsub.
str = "a\n\n\nb\n\n\n\n\n\nc"
str.squeeze("\n") # => "a\nb\nc"
You need to match more than one newline up to an infinite amount. Your code example will work with just a minor tweak:
str.gsub!(/\n+/, "\n")
For example:
str = "this\n\n\nis\n\n\n\n\na\ntest"
str.gsub!(/\n+/, "\n") # => "this\nis\na\ntest"
are you sure it shouldn't be /\n\n\n/, "\n" that what you seem to be wanting in your question above.
also, are you sure it's not doing a windows new-line "\r\n"?
EDIT: Additional info
Per Comment
"The amount of newlines can change. Different lines have between 2 and 5 newlines."
if you only want to hit the 2-5 lines try this
/\n{2,5}/, "\n"
Simply splitting and recombining the lines will give the desired result
>> "one\ntwo\n\nthree\n".split.join("\n")
=> "one\ntwo\nthree"
Edit: I just noticed this will replace ALL whitespace substrings with newlines, e.g.
>> "one two three\n".split.join("\n")
=> "one\ntwo\nthree"
First check that this is what you want!
Simply calling split will also trim out all of your whitespace.
You need to pass \n to split
>> "one ok \ntwo\n\nthree\n".split(/\n+/).join("\n")
=> "one ok \ntwo\nthree"
Additionally, also works with
spaces on blank lines
n number of back to back blank lines
str.gsub! /\n^\s*\n/, "\n\n"
where,
\n is of course newline
\s is space
denotes 1 or more spaces along when used after \s
Try This It Worked for me:
s = test\n\n\nbar\n\n\nfooo
s.gsub("\n\n", '')
Ruby needs the backslashes escaped differently than you have provided.
str.sub!("\\\\n+\\\\n","\\\\n")
http://www.ruby-forum.com/topic/176239