Javascript Regex I'm struggling with

Question

I am admittedly NOT a regex person but usually I can figure my way around something. This one has me stumped...

I need to match and replace a double greater than str (>>) that has an optional leading space. I know this doesn't work but something along the lines of...

/\s\s+[>>]/

But that's obviously no good.

Would appreciate any help. This site has been an amazing resource for me over the years and I can't believe I'm only getting around to posting something now, so it goes to show even a knucklehead like me has been able to benefit without bothering people... until now:) Thanks in advance.

do you want it to replace the optional leading space in addition to the >> if found? — magritte
– magritte, Commented Mar 14, 2013 at 21:37

ericmux · Accepted Answer · 2013-03-14 21:43:26Z

1

For >> both inside a string and with leading whitespace, try:

/(\s*)(>>){1}/

answered Mar 14, 2013 at 21:43

ericmux

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1 Comment

ericmux Over a year ago

you could just use />>/ but i guess the regex above makes the replacement job easier.

Denys Séguret · Accepted Answer · 2013-03-14 21:35:42Z

0

If you want the space to be optional, then you can simply do this :

/>>/

And you may use it as a replacement pattern with the g modifier :

str = str.replace(/>>/g, 'something')

If you want to check that a string is >> with maybe some space before, then use

/^\s?>>$/

answered Mar 14, 2013 at 21:35

Denys Séguret

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4 Comments

Wouter J Over a year ago

or just '>>' for simple string replaces

Denys Séguret Over a year ago

@WouterJ If you want to do more than one replacement, you must use a regex : myString.replace(/>>/g, '')

Wouter J Over a year ago

oh? I thought the g modifier was only usefull in matching, not in replacing. (in PHP, all replaces will be global by default)

Pedro Over a year ago

Thanks dystroy -- /\s?>>$/ ended up being the winner (without the caret because the pattern might not be expressly at the head of the string). Testing now and seems to be working flawlessly. Thank you!

TAS · Accepted Answer · 2013-03-14 21:50:45Z

0

Breaking down your example:

\s will match any white-space character
\s+ will match one or more white-space characters
[>>] will match one > (see more below on this)

So your expression will match a > preceeded by at least two white-space characters.

If you want to match zero-or-more you will have to use *; fex \s*.

Square brackets are used to denote sets of characters, and will match any of the characters in the set; fex [abc] will match a, b or c, but only one character at time.

Single characters in a regular expression will match that character; fex > will match one greater-than sign.

Putting it together we get the following regular expression for your case:

/\s*>>/

answered Mar 14, 2013 at 21:50

TAS

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Comments

user829323 · Accepted Answer · 2013-03-14 22:17:47Z

0

If you want it to match an unlimited amount of leading space characters:

/ *>>/

If you want it to match 0 or 1 leading space character:

/ ?>>/

edited Mar 14, 2013 at 22:17

answered Mar 14, 2013 at 21:44

user829323

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1 Comment

MikeM Over a year ago

+ means one or more, use ? for zero or one.

Amrendra · Accepted Answer · 2013-03-15 07:33:25Z

0

use this :

str.replace(/\s+>>/g, 'whatever');

answered Mar 15, 2013 at 7:33

Amrendra

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OregonTrail · Accepted Answer · 2013-03-16 19:54:42Z

0

This regex should work.

/\s*[>]{2}/

This is cleaner

/\s*>>/

Tested:

var pattern = /\s*>>/;
s1 = "             >>";
s2 = ">>";
s3 = ">> surrounding text";
s4 = "surrounding  >> text";
s5 = "surrounding>>text";

s1.match(pattern);
["             >>"]
s2.match(pattern);
[">>"]
s3.match(pattern);
[">>"]
s4.match(pattern);
["  >>"]
s5.match(pattern);
[">>"]

Replacement example

var pattern = /\s*>>/;
var s6 = "    >> surrounding text";
s6.replace(pattern, ">");
"> surrounding text"

edited Mar 16, 2013 at 19:54

answered Mar 14, 2013 at 21:36

OregonTrail

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1 Comment

FThompson Over a year ago

Or just >> for that matter.

General Grievance · Accepted Answer · 2023-05-02 21:14:47Z

0

This should work with the optional space.

/\s{0,}>>/g

edited May 2, 2023 at 21:14

General Grievance

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answered Mar 14, 2013 at 21:53

heyomi

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