Ruby regex matching a line in an inputted text file string

Question

I need to match a line in an inputted text file string and wrap that captured line with a character for example.

For example imagine a text file as such:

test
foo
test
bar

I would like to use gsub to output:

XtestX
XfooX
XtestX
XbarX

I'm having trouble matching a line though. I've tried using regex starting with ^ and ending with $, but it doesn't seem to work? Any ideas?

I have a text file that has the following in it:

test
foo
test
bag

The text file is being read in as a command line argument.

So I got (for example just trying to wrap test)

string = IO.read(ARGV[0])
string = string.gsub(/^(test)$/,'X\1X')

puts string

It outputs the exact same thing that is in the text file.

I've tried

string = string.gsub(/^(.*)$/, 'X\1X')

This outputs:

Xtest
Xfoo
Xtest
Xbar

...why?

Okay so I backspaced the last line of the text file and now I am getting this...

Xtest
Xfoo
Xbar
XtestX

According to your regex, you're expecting only those lines which starts with test, but your desired output is different! — A human being, Apr 13 '13 at 19:53
@UpasanaShukla what do you mean? My example code is attempting to wrap test with Xs so my output should include everything the same with XtestX and it doesn't. — Tommy, Apr 13 '13 at 19:57
See your desired output, in that replacement is being done in every line whether it starts with test or not. ain't it? — A human being, Apr 13 '13 at 20:00
according to your regex, "foo" shouldn't be replaced with XfooX — A human being, Apr 13 '13 at 20:01
So what. That doesn't explain why test isn't being wrapped with Xs. — Tommy, Apr 13 '13 at 20:02
@Tommy why you stick into `regex`. there are other way to do this. — Arup Rakshit, Apr 13 '13 at 20:06
@Tommy well, it's working fine on my system, I'm getting the desired output — A human being, Apr 13 '13 at 20:10
I'm using ruby 1.9.3. And @UpasanaShukla it's stupid because I'm literally copying and pasting exactly what people have been telling me that works and it just doesn't. — Tommy, Apr 13 '13 at 20:15
@Tommy After this line: `string = IO.read(ARGV[0])`, can you put print the string with `p` and give us the output (i.e `p string`)? (I know it should be the same as the file, but i want to make sure) — fmendez, Apr 13 '13 at 20:17
Check out my newest update. It recognized only the last line afted I deleted a blank line at the bottom. — Tommy, Apr 13 '13 at 20:18
@fmendex "test\r\nfoo\r\nbar\r\ntest" hmm so returns don't count as new lines? — Tommy, Apr 13 '13 at 20:21
probably you should have a look on how regex' `^` and `$` works — ted, Apr 13 '13 at 20:23
I guess I'm running Mac but am running it through a Windows virtual machine lol so it should be running on Windows. — Tommy, Apr 13 '13 at 20:24
Regular Expression to match cross platform newline characters http://stackoverflow.com/questions/1331815/regular-expression-to-match-cross-platform-newline-characters — ted, Apr 13 '13 at 20:32

user21033168 · Accepted Answer · 2013-04-13T20:44:23.537

2

string = "test\r\nfoo\r\ntest\r\nbar"
string = string.gsub(/^test(?=\r?\n)/, 'X\&X').delete(?\r)
puts string

edited Apr 13 '13 at 20:44

answered Apr 13 '13 at 20:27

user21033168

444
1
4
13

Thanks. It was definitely a problem with the \r's. I got rid of them and it works now. – Tommy Apr 13 '13 at 20:34

score 0 · Answer 2 · answered Apr 13 '13 at 20:24

0

It works fine for me in Ruboto IRB on my phone. Could you make a self-contained one-line example and post it? No file IO should be necessary. What ruby version do you use?

I suspect your program just has a typo.

answered Apr 13 '13 at 20:24

David Grayson

84,103
24
152
189

My program definitely does not have a typo. If I print my inputted string I get "test\r\nfoo\r\nbar\r\ntest" Does it not match the \r's or something? – Tommy Apr 13 '13 at 20:26
puts "test\r\nfoo\r\nbar\r\ntest".gsub(/^(.*)$/, 'X\1X') that outputs what I've showed with the Xtest Xfoo Xbar XtestX – Tommy Apr 13 '13 at 20:29

score 0 · Answer 3 · answered Apr 13 '13 at 20:34

Problem is because of dos line endings(\r\n), so for getting rid of this, there is a flip command (in MAC, if I'm correct) for converting dos line endings to mac line endings(\r). Search for it and convert dos line endings to mac line endings before using that text file.

Ruby regex matching a line in an inputted text file string

3 Answers3

Linked