Java regexp groups replacements

Question

Is there a way to transform the String

"m1, m2, m3"

to the following

"m1/build, m2/build, m3/build"

only by using String.replaceAll(regex, replacement) method?

So far this is my best attempt:

System.out.println("m1, m2, m3".replaceAll("([^,]*)", "$1/build"));
>>> m1/build/build, m2/build/build, m3/build/build

As you can see the output is incorrect. However, using the same regexp in Linux's sed command gives correct output:

echo 'm1, m2, m3' | sed -e 's%\([^,]*\)%\1/build%g'
>>> m1/build, m2/build, m3/build

Sergey Kalinichenko · Accepted Answer · 2012-07-13 21:00:28Z

5

If you look at the problem from the other end (quite literally!) you get an expression that looks for terminators, rather than for the content. This expression worked a lot better:

System.out.println("m1, m2, m3".replaceAll("(\\s*(,|$))", "/build$1"));

Here is a link to this program on ideone.

edited Jul 13, 2012 at 21:00

answered Jul 13, 2012 at 20:41

Sergey Kalinichenko

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4 Comments

BlackVegetable Over a year ago

That's the way I was thinking of doing it. But don't you have /build and $1 swapped?

Sergey Kalinichenko Over a year ago

@BlackVegetable Since I'm matching the terminator, not the content, the $1 belongs at the end.

Michal Vician Over a year ago

Nice. However this solution will not work if there are spaces between commas. E.g. for input 'm1 , m2, m3 ' the output would be incorrect: 'm1 /build, m2 /build,m3 /build'. The second answer which uses (\w+) as a regexp can cope with this situation.

Sergey Kalinichenko Over a year ago

@miso Not that it mattered much, but the "space before comma" was easy to address (please see the edit). I liked the \\w+ solution better, though :)

Kobi · Accepted Answer · 2012-07-13 20:41:24Z

4

([^,]*) can match the empty string, it can even match between two spaces. Try ([^,]+) or (\w+).

Another minor note - you can use $0 to refer to the whole matched string, avoiding the captured group:

System.out.println("m1, m2, m3".replaceAll("\\w+", "$0/build"));

answered Jul 13, 2012 at 20:41

Kobi

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