I'm trying to write a ruby script that will read through a CSV file and prepend information to certain cells (for instance adding a path to a file). I am able to open and mutate the text just fine, but am having issues writing back to the CSV without overriding everything. This is a sample of what I have so far:
CSV.foreach(path) { |row|
text = row[0].to_s
new_text = "test:#{text}"
}
I would like to add something within that block that would then write new_textback to the same reference cell(row) in the file. The only way I have to found to write to a file is
CSV.open(path, "wb") { |row|
row << new_text
}
But I think that is bad practice since you are reopening the file within the file block already. Is there a better way I could do this?
EX: I have a CSV file that looks something like:
file,destination
test.txt,A101
and need it to be:
file,destination
path/test.txt,id:A101
Hope that makes sense. Thanks in advance!
Depending on the size if the file, you might consider loading the contents of the file into a local variable and then manipulating that, overwriting the original file.
lines = CSV.read(path)
File.open(path, "wb") do |file|
lines.each do |line|
text = line[0].to_s
line[0] = "test:#{text}" # Replace this with your editing logic
file.write CSV.generate_line(line)
end
end
Alternately, if the file is big, you could write each modified line to a new file along the way and then replace the old file with the new one at the end.
Given that you don't appear to be doing anything that draws on CSV capabilities, I'd recommend using Ruby's "in-place" option variable $-i.
Some of the stats software I use wants just the data, and can't deal with a header line. Here's a script I wrote a while back to (appear to) strip the first line out of one or more data files specified on the command-line.
#! /usr/bin/env ruby -w
#
# User supplies the name of one or more files to be "stripped"
# on the command-line.
#
# This script ignores the first line of each file.
# Subsequent lines of the file are copied to the new version.
#
# The operation saves each original input file with a suffix of
# ".orig" and then operates in-place on the specified files.
$-i = ".orig" # specify backup suffix
oldfilename = ""
ARGF.each do |line|
if ARGF.filename == oldfilename # If it's an old file
puts line # copy lines through.
else # If it's a new file remember it
oldfilename = ARGF.filename # but don't copy the first line.
end
end
Obviously you'd want to change the puts line pass-through to whatever edit operations you want to perform.
I like this solution because even if you screw it up, you've preserved your original file as its original name with .orig (or whatever suffix you choose) appended.
The code I'm working with at the moment is supposed to spit back every line of information in one text document that contains the word "DEBUG" and then paste it in a new text document titled "debug.txt".
For whatever reason it is only printing the final line into the new text document and I have no clue why. However, another function is to spit back every line to the command terminal, and it does that successfully, it just won't write them all to the file.
log_file = File.open("main_file.rb")
File.readlines(log_file).each do |line|
if line.include? "DEBUG"
puts line
File.open("debug.txt", "w") do |out|
out.puts line
end
end
end
You're overwriting the file every time you find a DEBUG line in main_file. You have your blocks backwards. The File.open('debug.txt') should be outside of the File.readlines.
Like this:
log_file = File.open("main_file.rb")
File.open("debug.txt", "w") do |out|
File.readlines(log_file).each do |line|
if line.include? "DEBUG"
puts line
out.puts line
end
end
end
You could also open the file in append mode by passing 'a' instead of 'w' in your File.open('debug.txt') call but this would be needlessly reopening the file every time you find a line that contains DEBUG in it. It would be better to open the debug file once for writing and using the file handle from there on as I show above.
Write it like this:
File.open("debug.txt", "w") do |out|
File.foreach("main_file.rb") do |line|
if line['DEBUG']
puts line
out.puts line
end
end
end
You need to:
Open the output file.
Iterate over the lines in the input file.
For each line, check to see if it contains the string you want.
If so, write it.
Loop until the input file is completely read.
Close the output file.
Notice I don't open the file for output as a single step. Ruby's use of blocks are really handy: By passing a block to open, Ruby will close the file when the block exits, avoiding the problem of open files hanging around to clutter memory or consume available file handles.
Use foreach to read the file. It reads a single line at a time and is extremely fast. It's also scalable, which means it'll work for a one-line file or a 10-million line file equally well. Using readlines, as in your code, results in Ruby loading the entire file into memory, splitting it into separate lines, then iterating over them. That can cause real problems if your input file exceeds available RAM.
line['DEBUG'] is shorthand for "do a substring match for this text". See String#[] for more information.
I am trying to create a ruby script that loads 2 .sql files and removes all strings that begin with 'AUTO_INCREMENT='
There are multiple occurrences of this in my .sql files and all I want is them to be removed from both files.
Thanks for any help or input as I am new to ruby and decided to give it a try.
Given the right regexp (the one below might not be the most correct given the syntax), and the answer given there to a similar question, it is rather straightforward to put a script together:
file_names = ['file1.sql', 'file2.sql']
file_names.each do |file_name|
text = File.read(file_name)
File.open(file_name, 'wb') do
|file|
file.write(text.gsub(/\s*AUTO_INCREMENT\s*(\=\s*[0-9]+)?/, ""))
end
end
Have you tried using Regex for this? If you want to remove the whole line, you could simply match ^AUTO_INCREMENT=.+$ and replace it with an empty string. That pattern should match an entire line beginning with AUTO_INCREMENT.
Here's a good site to learn Regex if you aren't familiar with it:
Hope that works for you.
You should read up on IO, String, Array for more details on methods you can use.
Here's how you might read, modify, and save the contents of one file:
# Opens a file for reading.
file = File.open("file1.txt")
# Reads all the contents into the string 'contents'.
contents = file.read
file.close
# Splits contents into an array of strings, one for each line.
lines = contents.split("\n")
# Delete any lines that start with AUTO_INCREMENT=
lines.reject! { |line| line =~ /^AUTO_INCREMENT=/ }
# Join the lines together into one string again.
new_contents = lines.join("\n")
# Open file for writing.
file = File.open("file1.txt", "w")
# Save new contents.
file.write(new_contents)
file.close
I'm looking for a script to search a file (or list of files) for a pattern and, if found, replace that pattern with a given value.
Thoughts?
Disclaimer: This approach is a naive illustration of Ruby's capabilities, and not a production-grade solution for replacing strings in files. It's prone to various failure scenarios, such as data loss in case of a crash, interrupt, or disk being full. This code is not fit for anything beyond a quick one-off script where all the data is backed up. For that reason, do NOT copy this code into your programs.
Here's a quick short way to do it.
file_names = ['foo.txt', 'bar.txt']
file_names.each do |file_name|
text = File.read(file_name)
new_contents = text.gsub(/search_regexp/, "replacement string")
# To merely print the contents of the file, use:
puts new_contents
# To write changes to the file, use:
File.open(file_name, "w") {|file| file.puts new_contents }
end
Actually, Ruby does have an in-place editing feature. Like Perl, you can say
ruby -pi.bak -e "gsub(/oldtext/, 'newtext')" *.txt
This will apply the code in double-quotes to all files in the current directory whose names end with ".txt". Backup copies of edited files will be created with a ".bak" extension ("foobar.txt.bak" I think).
NOTE: this does not appear to work for multiline searches. For those, you have to do it the other less pretty way, with a wrapper script around the regex.
Keep in mind that, when you do this, the filesystem could be out of space and you may create a zero-length file. This is catastrophic if you're doing something like writing out /etc/passwd files as part of system configuration management.
Note that in-place file editing like in the accepted answer will always truncate the file and write out the new file sequentially. There will always be a race condition where concurrent readers will see a truncated file. If the process is aborted for any reason (ctrl-c, OOM killer, system crash, power outage, etc) during the write then the truncated file will also be left over, which can be catastrophic. This is the kind of dataloss scenario which developers MUST consider because it will happen. For that reason, I think the accepted answer should most likely not be the accepted answer. At a bare minimum write to a tempfile and move/rename the file into place like the "simple" solution at the end of this answer.
You need to use an algorithm that:
Reads the old file and writes out to the new file. (You need to be careful about slurping entire files into memory).
Explicitly closes the new temporary file, which is where you may throw an exception because the file buffers cannot be written to disk because there is no space. (Catch this and cleanup the temporary file if you like, but you need to rethrow something or fail fairly hard at this point.
Fixes the file permissions and modes on the new file.
Renames the new file and drops it into place.
With ext3 filesystems you are guaranteed that the metadata write to move the file into place will not get rearranged by the filesystem and written before the data buffers for the new file are written, so this should either succeed or fail. The ext4 filesystem has also been patched to support this kind of behavior. If you are very paranoid you should call the fdatasync() system call as a step 3.5 before moving the file into place.
Regardless of language, this is best practice. In languages where calling close() does not throw an exception (Perl or C) you must explicitly check the return of close() and throw an exception if it fails.
The suggestion above to simply slurp the file into memory, manipulate it and write it out to the file will be guaranteed to produce zero-length files on a full filesystem. You need to always use FileUtils.mv to move a fully-written temporary file into place.
A final consideration is the placement of the temporary file. If you open a file in /tmp then you have to consider a few problems:
If /tmp is mounted on a different file system you may run /tmp out of space before you've written out the file that would otherwise be deployable to the destination of the old file.
Probably more importantly, when you try to mv the file across a device mount you will transparently get converted to cp behavior. The old file will be opened, the old files inode will be preserved and reopened and the file contents will be copied. This is most likely not what you want, and you may run into "text file busy" errors if you try to edit the contents of a running file. This also defeats the purpose of using the filesystem mv commands and you may run the destination filesystem out of space with only a partially written file.
This also has nothing to do with Ruby's implementation. The system mv and cp commands behave similarly.
What is more preferable is to open a Tempfile in the same directory as the old file. This ensures that there will be no cross-device move issues. The mv itself should never fail, and you should always get a complete and untruncated file. Any failures, such as device out of space, permission errors, etc., should be encountered during writing the Tempfile out.
The only downsides to the approach of creating the Tempfile in the destination directory are:
Sometimes you may not be able to open a Tempfile there, such as if you are trying to 'edit' a file in /proc for example. For that reason you might want to fall back and try /tmp if opening the file in the destination directory fails.
You must have enough space on the destination partition in order to hold both the complete old file and the new file. However, if you have insufficient space to hold both copies then you are probably short on disk space and the actual risk of writing a truncated file is much higher, so I would argue this is a very poor tradeoff outside of some exceedingly narrow (and well-monitored) edge cases.
Here's some code that implements the full-algorithm (windows code is untested and unfinished):
#!/usr/bin/env ruby
require 'tempfile'
def file_edit(filename, regexp, replacement)
tempdir = File.dirname(filename)
tempprefix = File.basename(filename)
tempprefix.prepend('.') unless RUBY_PLATFORM =~ /mswin|mingw|windows/
tempfile =
begin
Tempfile.new(tempprefix, tempdir)
rescue
Tempfile.new(tempprefix)
end
File.open(filename).each do |line|
tempfile.puts line.gsub(regexp, replacement)
end
tempfile.fdatasync unless RUBY_PLATFORM =~ /mswin|mingw|windows/
tempfile.close
unless RUBY_PLATFORM =~ /mswin|mingw|windows/
stat = File.stat(filename)
FileUtils.chown stat.uid, stat.gid, tempfile.path
FileUtils.chmod stat.mode, tempfile.path
else
# FIXME: apply perms on windows
end
FileUtils.mv tempfile.path, filename
end
file_edit('/tmp/foo', /foo/, "baz")
And here is a slightly tighter version that doesn't worry about every possible edge case (if you are on Unix and don't care about writing to /proc):
#!/usr/bin/env ruby
require 'tempfile'
def file_edit(filename, regexp, replacement)
Tempfile.open(".#{File.basename(filename)}", File.dirname(filename)) do |tempfile|
File.open(filename).each do |line|
tempfile.puts line.gsub(regexp, replacement)
end
tempfile.fdatasync
tempfile.close
stat = File.stat(filename)
FileUtils.chown stat.uid, stat.gid, tempfile.path
FileUtils.chmod stat.mode, tempfile.path
FileUtils.mv tempfile.path, filename
end
end
file_edit('/tmp/foo', /foo/, "baz")
The really simple use-case, for when you don't care about file system permissions (either you're not running as root, or you're running as root and the file is root owned):
#!/usr/bin/env ruby
require 'tempfile'
def file_edit(filename, regexp, replacement)
Tempfile.open(".#{File.basename(filename)}", File.dirname(filename)) do |tempfile|
File.open(filename).each do |line|
tempfile.puts line.gsub(regexp, replacement)
end
tempfile.close
FileUtils.mv tempfile.path, filename
end
end
file_edit('/tmp/foo', /foo/, "baz")
TL;DR: That should be used instead of the accepted answer at a minimum, in all cases, in order to ensure the update is atomic and concurrent readers will not see truncated files. As I mentioned above, creating the Tempfile in the same directory as the edited file is important here to avoid cross device mv operations being translated into cp operations if /tmp is mounted on a different device. Calling fdatasync is an added layer of paranoia, but it will incur a performance hit, so I omitted it from this example since it is not commonly practiced.
There isn't really a way to edit files in-place. What you usually do when you can get away with it (i.e. if the files are not too big) is, you read the file into memory (File.read), perform your substitutions on the read string (String#gsub) and then write the changed string back to the file (File.open, File#write).
If the files are big enough for that to be unfeasible, what you need to do, is read the file in chunks (if the pattern you want to replace won't span multiple lines then one chunk usually means one line - you can use File.foreach to read a file line by line), and for each chunk perform the substitution on it and append it to a temporary file. When you're done iterating over the source file, you close it and use FileUtils.mv to overwrite it with the temporary file.
Another approach is to use inplace editing inside Ruby (not from the command line):
#!/usr/bin/ruby
def inplace_edit(file, bak, &block)
old_stdout = $stdout
argf = ARGF.clone
argf.argv.replace [file]
argf.inplace_mode = bak
argf.each_line do |line|
yield line
end
argf.close
$stdout = old_stdout
end
inplace_edit 'test.txt', '.bak' do |line|
line = line.gsub(/search1/,"replace1")
line = line.gsub(/search2/,"replace2")
print line unless line.match(/something/)
end
If you don't want to create a backup then change '.bak' to ''.
This works for me:
filename = "foo"
text = File.read(filename)
content = text.gsub(/search_regexp/, "replacestring")
File.open(filename, "w") { |file| file << content }
Here's a solution for find/replace in all files of a given directory. Basically I took the answer provided by sepp2k and expanded it.
# First set the files to search/replace in
files = Dir.glob("/PATH/*")
# Then set the variables for find/replace
#original_string_or_regex = /REGEX/
#replacement_string = "STRING"
files.each do |file_name|
text = File.read(file_name)
replace = text.gsub!(#original_string_or_regex, #replacement_string)
File.open(file_name, "w") { |file| file.puts replace }
end
require 'trollop'
opts = Trollop::options do
opt :output, "Output file", :type => String
opt :input, "Input file", :type => String
opt :ss, "String to search", :type => String
opt :rs, "String to replace", :type => String
end
text = File.read(opts.input)
text.gsub!(opts.ss, opts.rs)
File.open(opts.output, 'w') { |f| f.write(text) }
If you need to do substitutions across line boundaries, then using ruby -pi -e won't work because the p processes one line at a time. Instead, I recommend the following, although it could fail with a multi-GB file:
ruby -e "file='translation.ja.yml'; IO.write(file, (IO.read(file).gsub(/\s+'$/, %q('))))"
The is looking for white space (potentially including new lines) following by a quote, in which case it gets rid of the whitespace. The %q(')is just a fancy way of quoting the quote character.
Here an alternative to the one liner from jim, this time in a script
ARGV[0..-3].each{|f| File.write(f, File.read(f).gsub(ARGV[-2],ARGV[-1]))}
Save it in a script, eg replace.rb
You start in on the command line with
replace.rb *.txt <string_to_replace> <replacement>
*.txt can be replaced with another selection or with some filenames or paths
broken down so that I can explain what's happening but still executable
# ARGV is an array of the arguments passed to the script.
ARGV[0..-3].each do |f| # enumerate the arguments of this script from the first to the last (-1) minus 2
File.write(f, # open the argument (= filename) for writing
File.read(f) # open the argument (= filename) for reading
.gsub(ARGV[-2],ARGV[-1])) # and replace all occurances of the beforelast with the last argument (string)
end
EDIT: if you want to use a regular expression use this instead
Obviously, this is only for handling relatively small text files, no Gigabyte monsters
ARGV[0..-3].each{|f| File.write(f, File.read(f).gsub(/#{ARGV[-2]}/,ARGV[-1]))}
I am using the tty-file gem
Apart from replacing, it includes append, prepend (on a given text/regex inside the file), diff, and others.