How to replace multiple slash and backslash in a string with a single one?

Question

My goal is to replace all "/" and "\" with one "\".

Input:

String path = "H\\\\\\\\\\ello///Wo\\rld\\!////";

Output:

String path = "H\ello\Wo\rld\!\";

Question:

Is there a way to do that all in one single line?

My solution (working!):

change all to the same char
replace all "/" with one Slash
put it back to normal

I learned that I need regex and that "[X]+" will put all possible combinations eg. "XXfXfXXXX" to "XfXfX".

I am searching for something like: (pseudocode)

path = path.replaceAll("[\\/]+", "\\");

I tried some combinations of that but everytime it throw errors.

My Solution:

path = path.replace("\\", "/");
path = path.replaceAll("[/]+", "/");

pfad = pfad.replace("/", "\\");

I'm afraid you'll have to iterate here thru the chars one by one — Naya, Apr 29 '19 at 13:27
Why do you want to replace ``\`` with ``\``? It doesn't change anything. Do you perhaps want to replace *series* of ``\`` and `/` with single ``\``? — Pshemo, Apr 29 '19 at 13:29
Try `.replaceAll("[\\\\/]+", "\\\\")` if all chunks of 1 or more ``\`` and `/` chars should be replaced with one ``\``. — Wiktor Stribiżew, Apr 29 '19 at 13:30
Like I said, my solution works with that 3 steps, just thinking about if there s a way to put it in one replaceAll() — xentus, Apr 29 '19 at 13:31
What should be result of replacing ``\\\\//``? Should it be one ``\`` or maybe two ``\\`` (one for ``\\\\`` sequence and second for `//` sequence)? — Pshemo, Apr 29 '19 at 13:35
Are the strings in your example not escaped? Are you manipulating source code? I'm confused since the second string is a syntax error — Ruan Mendes, Apr 29 '19 at 13:56
My apologies if i confused you. No, I am not trying to manipulate "The Matrix" :D. It s just a short pic of a bigger problem. Of course it would be \\ in a String but I am not trying to get a "real" String as result. I missed one \ after "rld\" too — xentus, Apr 29 '19 at 14:36
See https://ideone.com/xhUr8C. One backslash is missing in your string literal before `!`, I added it there. — Wiktor Stribiżew, Apr 29 '19 at 14:41
@xentus I believe my first-posted solution in the [comment](https://stackoverflow.com/questions/55904397/how-to-replace-multiple-slash-and-backslash-in-a-string-with-a-single-one/55905751#comment98464405_55904397) is your answer. If yes, please consider accepting [my answer](https://stackoverflow.com/a/55905751/3832970). — Wiktor Stribiżew, Apr 30 '19 at 23:19

Michał Turczyn · Answer 1 · 2019-04-29T13:37:02.343

4

Try this pattern to match groups of slashes and backslashes: (?:\\+|\/+) and replace it with \\.

Explanation:

(?:...) - noncapturing group

\\+ - match one or more \

\/+ - match one or more /

| - alternation: match pattern on the right or on the left

Demo

Alternatively you could use pattern [\/\\]+, which matches one or more of \ or /

Another demo

edited Apr 29 '19 at 13:37

answered Apr 29 '19 at 13:30

Michał Turczyn

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This won't work if there's a mix of back- and forward-slashes. E.g. `H\\\\///\\\ello///Wo\\rld\!/\//`. It might be good enough for OP though ;) – SamWhan Apr 29 '19 at 13:34
@SamWhan That's why I included alternative, which would work in your scenario :) – Michał Turczyn Apr 29 '19 at 13:36
1

Simply `[\\\/]+` is sufficient – Strelok Apr 29 '19 at 14:00
@Strelok That's why I also suggested it – Michał Turczyn Apr 29 '19 at 14:01
@MichałTurczyn both of your examples do not produce correct result for "H\\\\///\\\ello///Wo\\rld\!/\//" or at least what I think it should be ("H\ello\Wo\rld\!\") – Strelok Apr 29 '19 at 14:03
Thx for the answers! It is nice to see that it is also possible to group them but of course best case would be to get all variations of '/' n '\'. Unfortunatly I get some errors: – xentus Apr 29 '19 at 14:14
I tried smth like the alternativ myself "[\/\\]+" , "[\\\/]+" results in: `test.java:6: error: illegal escape character` – xentus Apr 29 '19 at 14:16
Edit: pfad.replaceAll -> path.replaceAll – xentus Apr 29 '19 at 14:23
@xentus you need escape also escape character, so you need to write \\/ instead of just \/ ( you need to escape it first in a code, then in regular expression) – Michał Turczyn Apr 29 '19 at 14:41
1

No need to escape `/` char, it is not any special in a regex. – Wiktor Stribiżew Apr 29 '19 at 14:43

Wiktor Stribiżew · Answer 2 · 2019-04-29T14:50:11.690

Use

.replaceAll("[\\\\/]+", "\\\\")

See the regex graph:

The [\\/]+ pattern matches \ or / one or more times. The replacement pattern is \\ since a backslash in the replacement pattern is special in Java, it is used to escape the $ symbol that denotes a literal $ char. To match a literal backslash, you need to use four \ in the regex string literal.

See Java demo online:

String path = "H\\\\\\\\\\ello///Wo\\rld\\!////";
System.out.println(path.replaceAll("[\\\\/]+", "\\\\"));
// => H\ello\Wo\rld\!\

How to replace multiple slash and backslash in a string with a single one?

2 Answers2