Is this the most efficient way to get and remove first line in file?

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I have a script which, each time is called, gets the first line of a file. Each line is known to be exactly of the same length (32 alphanumeric chars) and terminates with "rn". After getting the first line, the script removes it.

This is done in this way:

$contents = file_get_contents($file));
$first_line = substr($contents, 0, 32);
file_put_contents($file, substr($contents, 32 + 2)); //+2 because we remove also the rn

Obviously it works, but I was wondering whether there is a smarter (or more efficient) way to do this?

In my simple solution I basically read and rewrite the entire file just to take and remove the first line.

Answers

There is no more efficient way to do this other than rewriting the file.

Tuesday, December 13, 2022

anton-tchekov

Let's say you have two files a.php and b.php on same folder.

Code on the file b.php

<?php

echo "hi";

?>

and code on a.php

<?php
$data = file_get_contents('b.php');
echo $data;

You access a.php on browser.

What do you see? A blank page.

Please check the page source now. It is there.

But not showing in browser as <?php is not a valid html tag. So browser can not render it properly to show as output.

<?php
$data = htmlentities(file_get_contents('b.php'));
echo $data;

Now you can see the output in browser.

Sunday, September 11, 2022

brightlancer

docs for io module

with open(fname, 'rb') as fh:
    first = next(fh).decode()

    fh.seek(-1024, 2)
    last = fh.readlines()[-1].decode()

The variable value here is 1024: it represents the average string length. I choose 1024 only for example. If you have an estimate of average line length you could just use that value times 2.

Since you have no idea whatsoever about the possible upper bound for the line length, the obvious solution would be to loop over the file:

for line in fh:
    pass
last = line

You don't need to bother with the binary flag you could just use open(fname).

ETA: Since you have many files to work on, you could create a sample of couple of dozens of files using random.sample and run this code on them to determine length of last line. With an a priori large value of the position shift (let say 1 MB). This will help you to estimate the value for the full run.

Saturday, October 1, 2022

ilpaijin

You probably want to try the PHP Tokenizer.

http://www.php.net/manual/en/ref.tokenizer.php

From an external script:

<?php

var_dump(token_get_all(file_get_contents('myscript.php')));

?>

Thursday, December 8, 2022

jimmont

Does this do it for you? Good old Descendants property.

string xmlInput = ...;
XDocument myDoc = XDocument.Parse(xmlInput);
//
List<XElement> someElements = myDoc.Descendants("a").ToList();
someElements.ForEach(x => x.Value = "Foo");
//
Console.WriteLine(myDoc);

Hmm, I see you have an attribute in there. Can do that too:

string xmlInput = //...
XDocument myDoc = XDocument.Parse(xmlInput);
//
List<XText> someText =
  myDoc.Descendants()
  .Nodes()
  .OfType<XText>()
  .Where(x => x.Value.StartsWith("{") && x.Value.EndsWith("}"))
  .ToList();
//
List<XAttribute> someAttributes =
  myDoc.Descendants()
  .Attributes()
  .Where(x => x.Value.StartsWith("{") && x.Value.EndsWith("}"))
  .ToList();
//
someText.ForEach(x => x.Value = "Foo");
someAttributes.ForEach(x => x.Value = "Bar");
//
Console.WriteLine(myDoc);

Ah, now with what you're expecting, I will make it work:

List<XElement> e = myDoc.Descendants("a").ToList();
e.Where(x => x.Attribute("name").Value == "username").Single().Value = "abc";
e.Where(x => x.Attribute("name").Value == "password").Single().Value = "abc";

Saturday, September 10, 2022

miguel_a._arilla

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Is this the most efficient way to get and remove first line in file?

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