Java: replace() the n pipe delimiter starting at the end with a regex

Question

I'm trying to replace the first "|" but by starting by the end of the string:

usr/bin/pipe|pipe|name|28|-rwxr-xr-x|root:root||46711b361edd4512814d9b367ae765f42a71d729708b3f2e162acb8f64592610|

my file name is pipe|pipe|name and i want my regex to return me usr/bin/pipe|pipe|name

I've begin by this regex: .([^\|]*)$ but I don't know how to go further in the pipes : https://regex101.com/r/ttbiab/3

And in Java:

String strLine = "usr/bin/pipe|pipe|name|28|-rwxr-xr-x|root:root||46711b361edd4512814d9b367ae765f42a71d729708b3f2e162acb8f64592610|";
strLine = strLine.replaceAll(".([^\\|]*)$", "[:124:]");
System.out.println("strLine : " + strLine);

Possible duplicate of [Replace last part of string](https://stackoverflow.com/questions/1660034/replace-last-part-of-string) — Konrad Höffner, Apr 23 '19 at 14:16
Can you provide examples? Not sure if you mean the first pipe in the string or the last pipe. — John, Apr 23 '19 at 14:18
What command is generating the string that you're trying to parse? Based on what you've shown, a filename might theoretically contain no pipes, one pipe, or multiple pipes, so you'll need to use something besides just the pipes to base your regex on. — Jordan, Apr 23 '19 at 14:24
I want to handle files with pipes ;) it's a scan agent who generates me a file with all the packages I've intalled on a linux machine — TheSmartMonkey, Apr 23 '19 at 14:28
Is your filename always guaranteed to contain a pipe? Could it have multiple pipes? — Jordan, Apr 23 '19 at 14:29
@Thefourthbird your example works for only 1 pipe and in java seem's complicated to handle for the replace — TheSmartMonkey, Apr 23 '19 at 14:34
Do you want to replace a pipe or do you want to get a match? — The fourth bird, Apr 23 '19 at 14:35
It's not guaranteed to have a pipe I just have a few who has it and it could have multiple pipes yes but my number of pipes after the filename is fix to 6 — TheSmartMonkey, Apr 23 '19 at 14:42

score 0 · Answer 1 · edited Apr 23 '19 at 15:30

0

You can try something like this [\|]([^\|]*[\|]){5}$. It matches the pipe count of 5 followed by first pipe from the ends.

edited Apr 23 '19 at 15:30

Wai Ha Lee

8,598
83
57
92

answered Apr 23 '19 at 15:20

Akshay Mishra

189
1
8

The fourth bird · Answer 2 · 2019-04-23T17:55:07.200

If there is a fixed number of 6 pipes until the end of the string, and you want to select the individual pipes before that to replace them, you could make use of \G to assert the position at the previous match and use a lookahead to assert that what is on the right is 6 times not a pipe followed by a pipe.

(?:([^\|]*)|\G(?!^))\|([^|]*)(?=(?:[^|]*\|){6})

In Java:

String regex = "(?:([^\\|]*)|\\G(?!^))\\|([^|]*)(?=(?:[^|]*\\|){6})";

(?: Non capturing group
- ([^\|]*) Capture in group 1 matching not a pipe 0+ times using a negated character class
- | OR
- \G(?!^) Assert position at the end of the previous match, not at the start
) Close non capturing group
\|([^|]*) Match a pipe and capture in group 2 match 0+ times not a pipe
(?= Non capturing group
- (?:[^|]*\|){6} Positive lookahead, assert what is on the right is 6 times not a pipe followed by a pipe
) Close non capturing group

Regex demo | Java demo

If you want to replace the pipe with for example #, then use the 2 capturing groups:

$1#$2

Jordan · Accepted Answer · 2019-04-23T17:10:49.370

Based on your comments, it looks like you don't know how many pipes will be in the filename, but you do know how many pipes are in the input string that aren't in the filename. In this case, regex may not be the best approach. There are a couple of different ways to do this, but perhaps one of the easiest to understand and maintain would be to split the String, and then recombine it with replacements where applicable:

String input = "usr/bin/pipe|pipe|name|28|-rwxr-xr-x|root:root||46711b361edd4512814d9b367ae765f42a71d729708b3f2e162acb8f64592610|";
String pipeReplacement = ":124:";
int numberOfPipesToKeep = 7;

String[] split = input.split("\\|");
StringBuilder sb = new StringBuilder();
for (int i = 0; i < split.length; i++) {
    sb.append(split[i]);
    if (i < split.length - numberOfPipesToKeep) {
        sb.append(pipeReplacement);
    } else {
        sb.append("|");
    }
}

String output = sb.toString();
System.out.println(output);

The above sample handles any number of pipes, is pretty configurable, and is (in my opinion) a lot easier to understand and debug than trying to use regular expressions.

Java: replace() the n pipe delimiter starting at the end with a regex

3 Answers3