Google doesn't give any great results for getting the last line of a file in groovy so I feel this question is necessary.
How does one get the last line of a file in groovy?
Get all lines, then get the last one:
def lines=new File("/home/user/somefile.txt").readLines()
def lastline=lines.get(lines.size()-1)
Or, if the file is dangerously large:
def last=new File('/home/user/somefile.txt').withReader { r-> r.eachLine {it} }
which is almost identical to asker's answer.
Here's what I ended up with:
new File("/home/user/somefile.txt").eachLine {
lastLine = it
}
.eachLine iterates through each line of the text file and lastLine is set to the current iteration until eachLine finishes going through the file. Pretty straightforward.
How does one get the last line of a file in groovy?
It depends on what you know about the file. If the lines in the file are fixed length then you could look at the file size, divide it by the length of each line and then use random file access to jump to the last line in the file and read it. That would be more efficient than reading the entire file. If you don't know the length of the lines then you are probably going to have to read the entire file and discard everything before the last line you read.
Related
Let's say i have the following file,
dummy_file.txt(contents below)
first line
third line
how can i add a line to that file right in the middle so the end result is:
first line
second line
third line
I have looked into opening the file with the append option, however that adds the line to the end of the file.
with open("dummy_file.txt", 'r') as file:
lines = file.readlines()
lines.insert(1, "second line\n")
with open("dummy_file.txt", 'w') as output:
output.writelines(lines)
So:
We open the file an read all the lines making a list.
We insert to the list the desired new line, using \n for a new line.
We open the file again but this time to write.
We write all the lines from the list.
But I wouldn't recommend this method, due it hight memory usage (if the file is big).
The standard file methods don't support inserting into the middle of a file. You need to read the file, add your new data to the data that you read in, and then re-write the whole file.
I am using Python 3.6.4 on Windows 10 with Fall Creators Update. I am attempting to read a XML file using the following code:
with open('file.xml', 'rt', encoding='utf8') as file:
for line in file.readline():
do_something(line)
readline() is returning a single character on each call, not a complete line. The file was produced on Linux, is definitely encoded as UTF8, has nothing special such as a BOM at the beginning and has been verified with a hex dump to contain valid data. The line end is 0x0a since it comes from Linux. I tried specifying -1 as the argument to readline(), which should be the default, without any change in behavior. The file is very large (>240GB) but the problem is occurring at the start of the file.
Any suggestions as to what I might be doing wrong?
readline() will return a single line as a string (which you then iterate over). You should probably use readlines() instead, as this will give you a list of lines which your for-loop will iterate over, one line at a time.
Even better, and more efficient:
for line in file:
do_something(line)
readline() returns a string representing a line in the file while readlines() returns a list, each item is a line. So it's clear that
for line in file.readline()
is iterating over a string, that's why you got a character
If you want to iterate over the file and avoid jamming your memory, try this:
line = '1'
while line:
line = f.readline()
if !line:
break
do_something(line)
or:
line = f.readline()
while line:
do_something(line)
line = f.readline()
By the way, beautifulsoup is a useful package for xml phrasing.
I am creating a program, which at the end of all the inputs, I write to a text file and it comes up as one big line. Other than going into my text file and manually changing it to multiple lines, how do you write to a python text file in separate lines?
Eta:
Line one that holds one piece of inputted information
Line two that holds another piece of inputted information
Line three that holds a final piece of inputted information
I've tried writing twice to a file before closing it, but it returns an error saying it expected 1 argument and received more.
You should post at least a failed attempt that we can fix; but, due to the simplistic nature of the problem, I'll just give a quick answer anyway.
Steps:
Open the file in write ('w') mode (note that this blanks the file)
Write a line
Write a new-line ('\n'). Note that this step can be combined with the previous
Repeat steps 2 and 3 for all your lines
Close the file.
So, here's an implementation of the above. Note how we can use a with statement to do the first and last steps in one (and other benefits).
lines = ['Line one', 'Line two', 'Line three']
with open('your_file.txt', 'w') as f:
for l in lines:
f.write(l + '\n')
The list name is disk and its below:
disks
['5000cca025884d5\n', '5000cca025a1ee6\n']
The file name is p and its below:
c0t5000CCA025884D5Cd0 solaris
/scsi_vhci/disk#g5000cca025884d5c
c0t5000CCA025A1EE6Cd0
/scsi_vhci/disk#g5000cca025a1ee6c
c3t50060E8007DB981Ad1
/pci#400/pci#1/pci#0/pci#8/SUNW,emlxs#0/fp#0,0/ssd#w50060e8007db981a,1
c3t50060E8007DB981Ad2
/pci#400/pci#1/pci#0/pci#8/SUNW,emlxs#0/fp#0,0/ssd#w50060e8007db981a,2
c3t50060E8007DB981Ad3
/pci#400/pci#1/pci#0/pci#8/SUNW,emlxs#0/fp#0,0/ssd#w50060e8007db981a,3
c3t50060E8007DB981Ad4
i want to search elements of a list in file
There are a couple of things to look at here:
I haven't actually used re.match() before, but I can see the first issue: Your list of disks has a newline character after every entry, so that will mess up matches. Also, re.match() only matches from the start of the line. Your lines start with numbers, so you need to search during the line, using re.search(). Finally, you should make it case insensitive; one option to d this is to make everything lowercase just as your disks list is.
try adapting your loop as so:
#.strip() will get rid of new lines and .lower() will make the string lowercase
for line in q:
if re.search(disks[0].strip(),line.lower()):
print line
If that doesn't fix it, I would try making it print out disks[0].strip() and line for every iteration of the loop (not just when it matches the if clause) to make sure it's reading in what you think it is.
I have a text file with special characters as well as normal characters. I am trying to read this file line by line. I have used
string[] lines = System.IO.File.ReadAllLines("Trial.txt");
To read it.
I used a break point and tried to find out the values stored in those lines. It broke some of the lines in between without finishing reading it and stored the rest in a new next line. When I checked the records, I found that the breaking occurs only at the point where there are special characters even though it doesn't happen with a particular special character. If the file has a total of 10 lines and if there is 1 line which has this problem, it reads a total of 11 lines. Can any of you guys pleas help me out with this? The text file is in UTF-8 format.
The File.ReadAllLines method splits the file on carriage return ('\r'), new line ('\n'), or a carriage return followed by a new line (taken from here: http://msdn.microsoft.com/en-us/library/s2tte0y1.aspx).
Check if the line that is not supposed to be split has either of those characters (judging from your reply to Luke Wyatt you probably have a new line ('\n') on that line at the point where it splits).