Regex: Retrieve number after repeated string

Question

Say I have a string:

\foo\junk\f0\morejunk\

How can I extract 'f0' from it using regex? I essentially only want to match an 'f' followed by a number, without it getting caught on strings beginning with 'f' not followed by a number.

I have tried the following:

(?<=f)(\d*)

But this gets stuck on the first 'f' in the string, 'foo' and doesn't match the latter case of 'f0'. How can I put a quantifier on a lookbehind to match the string I want?

another option could be to split the string by the '\' delimiter and try to match each split, but this seems unnecessary?

Ah I was using the wrong quantifier, thank you for pointing out my stupidity — BoyUnderTheMoon
– BoyUnderTheMoon, Commented Nov 11, 2015 at 11:08

Pranav C Balan · Accepted Answer · 2015-11-12 04:38:07Z

2

Look behind is not supported in JavaScript regex. You can use capture group. Also use + instead of *, since * matches 0 or more characters while + will match one or more of the preceding character.

var str='\\foo\\junk\\f0\\morejunk\\';
var res=str.match(/\\f(\d+)\\/)[1];
alert(res);

Update : If you want to match entire string then just use /f\d+/ no need of capturing group

var str='\\foo\\junk\\f0\\morejunk\\';
var res=str.match(/\\(f\d+)\\/)[1];
alert(res);

edited Nov 12, 2015 at 4:38

answered Nov 11, 2015 at 11:04

Pranav C Balan

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4 Comments

BoyUnderTheMoon Over a year ago

Thank you for your explination

Tushar Over a year ago

"How can I extract 'f0' from it using regex?", use /(f\d+)/.

Pranav C Balan Over a year ago

match(/f\d+/)[0] for extracting entire string

Max Zuber Over a year ago

This one is wrong. Such pattern will match any string like \foo\junk\junkf0junk\morejunk\. My solution posted below/above.

Toto · Accepted Answer · 2015-11-11 11:05:22Z

1

Why not simply:

/(f\d+)/

It matches f followed by one or more digits. The result is in group 1.

answered Nov 11, 2015 at 11:05

Toto

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3 Comments

Max Zuber Over a year ago

Apply this pattern for \foo\junk\junkf0junk\morejunk\

Toto Over a year ago

@MaxZuber: well, it gives f0, so what?

Max Zuber Over a year ago

According the last paragraph of the question, it should be junkf0junk and it doesn't match the pattern then

Max Zuber · Accepted Answer · 2015-11-11 11:10:30Z

0

var string = '\\foo\\junk\\f0\\morejunk\\';
var expression = /\\(f(\d+))\\/;
var matches_array = string.match(expression);

answered Nov 11, 2015 at 11:10

Max Zuber

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