Hi just getting into Ruby, and I am trying to learn some basic file reading commands, and I haven't found any solid sources yet.
I am trying to go through certain lines from that file, til the end of the file.
So in the file where it says FILE_SOURCES I want to read all the sources til end of file, and place them in a file.
I found printing the whole file, and replacing words in the file, but I just want to read certain parts in the file.
Usually you follow a pattern like this if you're trying to extract a section from a file that's delimited somehow:
open(filename) do |f|
state = nil
while (line = f.gets)
case (state)
when nil
# Look for the line beginning with "FILE_SOURCES"
if (line.match(/^FILE_SOURCES/))
state = :sources
end
when :sources
# Stop printing if you hit something starting with "END"
if (line.match(/^END/))
state = nil
else
print line
end
end
end
end
You can change from one state to another depending on what part of the file you're in.
I would do it like this (assuming you can read the entire file into memory):
source_lines = IO.readlines('source_file.txt')
start_line = source_lines.index{ |line| line =~ /SOURCE_LINE/ } + 1
File.open( 'other_file.txt', 'w' ) do |f|
f << source_lines[ start_line..-1 ].join( "\n" )
end
Relevant methods:
IO.readlines to read the lines into an array
Array#index to find the index of the first line matching a regular expression
File.open to create a new file on disk (and automatically close it when done)
Array#[] to get the subset of lines from the index to the end
If you can't read the entire file into memory, then I'd do a simpler variation on #tadman's state-based one:
started = false
File.open( 'other_file.txt', 'w' ) do |output|
IO.foreach( 'source_file.txt' ) do |line|
if started then
output << line
elsif line =~ /FILE_SOURCES/
started = true
end
end
end
Welcome to Ruby!
File.open("file_to_read.txt", "r") {|f|
line = f.gets
until line.include?("FILE_SOURCES")
line = f.gets
end
File.open("file_to_write.txt", "w") {|new_file|
f.each_line {|line|
new_file.puts(line)
}
new_file.close
}
f.close
}
IO functions have no idea what "lines" in a file are. There's no straightforward way to skip to a certain line in a file, you'll have to read it all and ignore the lines you don't need.
Related
I have my file
ppp.txt
mmm;2;nsfnjd;pet;
sadjjasjnsd;6;gdhjsd;pet;
gsduhdssdj;3;gsdhjhjsd;dog;
I need to write
nsfnjd
gsdhjhjsd
I use this code but only print the last line "gsdhjhjsd"
I dont know what is doing wrong
File.open("ppp.txt", "r") do |fi|
fi.readlines.each do |line|
parts = line.chomp.split(';')
if parts[1].to_i < 4
puts parts[2]
File.open("testxx.txt", "w+") do |f|
f. puts parts[2]
end
end
end
end
Please help me
Open the file using append mode, 'a+' instead of write mode 'w+', which overwrites the file, as the open command is called inside a loop.
Or open the write file prior to looping the lines of the read file.
open the file descriptor outside the loop
fo = File.open("testxx.txt","w+")
File.open("ppp.txt", "r") do |fi|
fi.readlines.each do |line|
parts = line.chomp.split(';')
fo.puts parts[2] if parts[1].to_i < 4
end
end
fo.close()
NOTE: Need to explicitly close fo, but file open with block; ruby close the file automatically (fi case).
I want to learn the simplest way to filter fileIN.txt and store results in fileOUT.txt. I have a logic to go thru each line, do grep and write line if match, but I think might something more powerful?
My file is 2G so I care about performance.
f = File.new("fileIN.txt")
text = f.read
if text =~ /foo|moo|woo/ then
#write fileOUT.txt?
end
I would go with:
begin
input = File.new('fileIN.txt', 'r')
File.open('fileOut.txt', 'w') do |output|
while line = file.gets
output.write line if line =~ /foo|moo|woo/
end
end
ensure
input && input.close
end
When I start printing lines from a file, I get this error
#<File:0x007ff65ee297b0>
Here is the code
require 'rubygems'
File.open("sample.txt", 'r') do |f|
puts f
end
You are printing the file object. To get the contents line by line, you can use File.foreach
File.foreach('sample.txt', 'r') do |line|
puts line # called for every line
end
To process the whole file at once, you can use the read method on the file object:
File.open('sample.txt', 'r') do |file|
puts file.read # called only once
end
This is not an error. It prints correctly one line which is your File object.
Here your create a file object and you did not ask it to fetch lines or anything else for that matter.
Several good answers already. But here is another way to do it with minimal change to your code:
File.open("sample.txt", 'r').each_line do |f|
puts f
end
Another way :
IO.foreach("sample.txt") {|line| line }
Or
File.foreach('sample.txt') {|line| line }
File::open returns file handle (which apparently is being printed out as #<File:0x007ff65ee297b0>.) If you need the file content line by line you might want to use IO::readlines:
IO.readlines("sample.txt").each do |line|
puts line
end
I want to add newline character below.
But the result is wrong.
Teach me what is wrong.
test.txt(before)
------------------
2014-09
2014-10
2014-11
------------------
test.txt(after)
------------------
2014-09
2014-10
2014-11
------------------
I make a ruby script below, but the result is wrong.
f = File.open("test.txt","r+")
f.each{|line|
if line.include?("2014-10")
f.puts nil
end
}
f.close
the result
------------------
2014-09
2014-10
014-11
------------------
To solve your problem, the easiest way is to create a new file to output your new text into. To do you'll need to open the input file and the output file and iterate each line of the file check the condition and put desired line into the output file.
Example
require 'fileutils'
File.open("text-output.txt", "w") do |output|
File.foreach("text.txt") do |line|
if line.include?("2014-10")
output.puts line + "\n"
else
output.puts line
end
end
end
FileUtils.mv("text-output.txt", "text.txt")
Easy way
File.write(f = "text.txt", File.read(f).gsub(/2014-10/,"2014-10\n"))
Reading and writing a file at the same time can get messy, same thing with other data structures like arrays. You should build a new file as you go along.
Some notes:
you should use the block form of File.open because it will stop you from forgetting to call f.close
puts nil is the same as puts without arguments
single quotes are preferred over double quotes when you don’t need string interpolation
you should use do ... end instead of { ... } for multi-line blocks
File.open(...).each can be replaced with File.foreach
the intermediate result can be stored in a StringIO object which will respond to puts etc.
Example:
require 'stringio'
file = 'test.txt'
output = StringIO.new
File.foreach(file) do |line|
if line.include? '2014-10'
output.puts
else
output << line
end
end
output.rewind
File.open(file, 'w') do |f|
f.write output.read
end
I am trying to recursively replace a whole line from index.html files into a directory with sub-directories.
The code above puts the right lines I'm searching with the var "pattern", but when I run it, it removes everything form my index.html files.
pattern = "Keyword"
replacement = "<td width=\"30\"><img src=\"styles/img/trans.gif\" width=\"30\"></td>"
Dir.glob('/Users/root/Desktop/directory/test/**/index.html') do |item|
next unless File.file?(item)
File.open(item, "w+:ASCII-8BIT") do |f|
f.each_line do |line|
if line.match(pattern)
my_line = line
line.sub(my_line, replacement)
end
end
end
end
What am I doing wrong ?
You need to read the file first, build the expected output, and then write it:
Dir.glob('/Users/root/Desktop/directory/test/**/index.html') do |item|
next unless File.file?(item)
output = IO.readlines(item).map do |line|
if line.match(pattern)
replacement
else
line
end
end
File.open(item, "w+:ASCII-8BIT") do |f|
f.write output.join
end
end
end
You use File.open with open mode w+ which, according to Ruby documentation, is:
"w+" Read-write, truncates existing file to zero length or creates a new file for reading and writing.
To read the file and put some lines use r:
File.open(item, "r:ASCII-8BIT")