Creating new variable from another via string manipulation

Question

Suppose, I have a variable $var1 which contains the followings:

$var1="../sidebar_items/uploaded_files/notices/circular.pdf";

Now, I want to create another variable $var2 which will hold the following value:

$var2="../dev/sidebar_items/uploaded_files/notices/circular.pdf";

I want to create $var2 with the help of $var1 via string manipulation. Is it possible to do so? How will I achieve that?

I'd refactor the whole system so you'd have just: $filename="/sidebar_items/uploaded_files/notices/circular.pdf"; The responsibility of deciding what directory to look in (.. or ../dev) is better kept to a dedicated part of the application for determining this. This way you keep the application responsibilities more loosely coupled and thus more maintainable. — Ultimater
– Ultimater, Commented Nov 22, 2018 at 6:54

M. Eriksson · Accepted Answer · 2018-11-22 06:32:33Z

1

Just use str_replace(). It returns the changed string but doesn't change the original variable so you can store the result in a new variable:

$var2 = str_replace('../', '../dev/', $var1);

answered Nov 22, 2018 at 6:32

M. Eriksson

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kungphu Over a year ago

I think this answer would be improved by limiting the replacement to the beginning of the string, rather than all instances of ../ throughout the string, since we don't know how user-uploaded filenames are being handled.

kungphu · Accepted Answer · 2018-11-22 06:52:26Z

It looks like you're allowing users to upload files and saving the filenames. That's potentially very dangerous depending on how you're dealing with them; if you are taking their string value and doing file system operations against it, you could end up with a user uploading a file with a name like ../../../../../usr/bin/php and risking allowing a delete operation against that file (if your permissions are set up really, really poorly) or, perhaps more realistically, using path manipulation to delete, modify, or overwrite any file owned by the web server user. index.php would be an obvious target.

You should consider keeping both paths in separate constants rather than using string manipulation to turn one into the other at runtime. You should also consider renaming user-uploaded files, or at least being very careful about how you store them with regard to naming based on how you access them in your code.

Parvej Alam · Accepted Answer · 2018-11-22 07:14:03Z

0

you could also use strtr() function of PHP

$var2 = strtr($var1, '../', '../dev/');

answered Nov 22, 2018 at 7:14

Parvej Alam

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Comments

Nigel Ren · Accepted Answer · 2018-11-22 07:21:31Z

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I'd approach it by separating out the file name using basename() and then having a variable which has the path to the dev directory. This allows you to change it to all sorts rather than limiting it to a minor change...

$var1="../sidebar_items/uploaded_files/notices/circular.pdf";
$devpath = "../dev/sidebar_items/uploaded_files/notices/";
echo $devpath.basename($var1);

gives...

../dev/sidebar_items/uploaded_files/notices/circular.pdf

answered Nov 22, 2018 at 7:21

Nigel Ren

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