Connecting Tech Pros Worldwide Forums | Help | Site Map
bytes > topic > javascript > answers

How to build a regular expression on runtime?

Harry
Guest
  
Posts: n/a
#1: Jul 23 '05
Hi there,

does anyone know how I can build a regular expression e.g. for the
string.search() function on runtime, depending on the content of
variables? Should be something like this:

var strkey = "something";
var str = "Somethin like this";

if( str.search( / + strkey + / ) > -1 )
{
...
}

TIA
Harry

Michael Winter
Guest
  
Posts: n/a
#2: Jul 23 '05

re: How to build a regular expression on runtime?

On 16 Aug 2004 09:15:34 -0700, Harry <harald.humml@t-systems.at> wrote:
[color=blue]
> does anyone know how I can build a regular expression e.g. for the
> string.search() function on runtime, depending on the content of
> variables?[/color]

[snip]

Use the regular expression constructor to create an object:

var re = new RegExp(pattern, flags);
var str = str.replace(re, replacement);

Both pattern and flags are strings (flags is optional), so remember to
escape characters properly. For example,

/\d/ becomes '\\d'

Notice that the forward slashes aren't present in the pattern.

Good luck,
Mike

--
Michael Winter
Replace ".invalid" with ".uk" to reply by e-mail
Alberto
Guest
  
Posts: n/a
#3: Jul 23 '05

re: How to build a regular expression on runtime?

Proceed as follows (one suggestion out of many of course):

<script><!--
var test_string="hallo guy hallo! I said hallo!";
var yourRegExp_as_text="\\w{5}"; //that checks for 5 letters long words
var regExpObject=new RegExp();
//now use the built in method compile
regExpObject.compile(yourRegExp_as_text, "gi");
/*the second argument takes in the so called modifiers. g stands fopr GLOBAL
scope (search ALL the occurrencies, that is), i stands for case INsensitive
search*/

//Now you have a valid regular expression
//use it with methods that are regular expression methods, instance
replace():
test_string=test_string.replace(regExpObject, "HI"); /*replaced hallo with
HI*/
alert(test_string)
//--></script>

For an overview of the javascript methods that deal with regular expressions
(NOT the best summary available online of course! just one among many
others!):
http://www.unitedscripters.com/spellbinder/regexp.html

I hope this helps
ciao
Alberto
http://www.unitedscripters.com/






"Harry" <harald.humml@t-systems.at> ha scritto nel messaggio
news:b3271585.0408160815.4ef7c45@posting.google.co m...[color=blue]
> Hi there,
>
> does anyone know how I can build a regular expression e.g. for the
> string.search() function on runtime, depending on the content of
> variables? Should be something like this:
>
> var strkey = "something";
> var str = "Somethin like this";
>
> if( str.search( / + strkey + / ) > -1 )
> {
> ...
> }
>
> TIA
> Harry[/color]
Alberto
Guest
  
Posts: n/a
#4: Jul 23 '05

re: How to build a regular expression on runtime?

PS if the line

//use it with methods that are regular expression methods, instance
replace():

gets broken like it does on my reader, eliminate that ISOLATED replace():
that was not code but a part of a comment

ciao
Alberto

"Alberto" <nospam@nospam.nospam> ha scritto nel messaggio
news:Jn8Uc.145762$5D1.7196307@news4.tin.it...[color=blue]
> Proceed as follows (one suggestion out of many of course):
>
> <script><!--
> var test_string="hallo guy hallo! I said hallo!";
> var yourRegExp_as_text="\\w{5}"; //that checks for 5 letters long words
> var regExpObject=new RegExp();
> //now use the built in method compile
> regExpObject.compile(yourRegExp_as_text, "gi");
> /*the second argument takes in the so called modifiers. g stands fopr[/color]
GLOBAL[color=blue]
> scope (search ALL the occurrencies, that is), i stands for case[/color]
INsensitive[color=blue]
> search*/
>
> //Now you have a valid regular expression
> //use it with methods that are regular expression methods, instance
> replace():
> test_string=test_string.replace(regExpObject, "HI"); /*replaced hallo[/color]
with[color=blue]
> HI*/
> alert(test_string)
> //--></script>
>
> For an overview of the javascript methods that deal with regular[/color]
expressions[color=blue]
> (NOT the best summary available online of course! just one among many
> others!):
> http://www.unitedscripters.com/spellbinder/regexp.html
>
> I hope this helps
> ciao
> Alberto
> http://www.unitedscripters.com/
>
>
>
>
>
>
> "Harry" <harald.humml@t-systems.at> ha scritto nel messaggio
> news:b3271585.0408160815.4ef7c45@posting.google.co m...[color=green]
> > Hi there,
> >
> > does anyone know how I can build a regular expression e.g. for the
> > string.search() function on runtime, depending on the content of
> > variables? Should be something like this:
> >
> > var strkey = "something";
> > var str = "Somethin like this";
> >
> > if( str.search( / + strkey + / ) > -1 )
> > {
> > ...
> > }
> >
> > TIA
> > Harry[/color]
>
>[/color]
Harry
Guest
  
Posts: n/a
#5: Jul 23 '05

re: How to build a regular expression on runtime?

Alberto,
Michael,

Thank you for your replies. The Problem is not to replace a string
with regexp. The Problem is to build a search-regexp dynamically at
runtime. Naturally I will search with regexp like this:

var somestring = "somecontent";
if( somestring.search( /some/ ) > -1 )
{
...
}

In this example, the problem is that the searchstring is hardcoded.
What I want is:

var somestringarray = new Array( "one", "two", "three" );
var somestring = "This is one of my favorite";
for( var i = 0; i < somestringarray.length; i++ )
{
if( somestring.search( somestringarray[ i ] ) > -1 )
{
...
break;
}
}

How can I achieve this?

TIA
Harry

"Alberto" <nospam@nospam.nospam> wrote in message news:<Hr8Uc.145776$5D1.7197081@news4.tin.it>...[color=blue]
> PS if the line
>
> //use it with methods that are regular expression methods, instance
> replace():
>
> gets broken like it does on my reader, eliminate that ISOLATED replace():
> that was not code but a part of a comment
>
> ciao
> Alberto
>
> "Alberto" <nospam@nospam.nospam> ha scritto nel messaggio
> news:Jn8Uc.145762$5D1.7196307@news4.tin.it...[color=green]
> > Proceed as follows (one suggestion out of many of course):
> >
> > <script><!--
> > var test_string="hallo guy hallo! I said hallo!";
> > var yourRegExp_as_text="\\w{5}"; //that checks for 5 letters long words
> > var regExpObject=new RegExp();
> > //now use the built in method compile
> > regExpObject.compile(yourRegExp_as_text, "gi");
> > /*the second argument takes in the so called modifiers. g stands fopr[/color]
> GLOBAL[color=green]
> > scope (search ALL the occurrencies, that is), i stands for case[/color]
> INsensitive[color=green]
> > search*/
> >
> > //Now you have a valid regular expression
> > //use it with methods that are regular expression methods, instance
> > replace():
> > test_string=test_string.replace(regExpObject, "HI"); /*replaced hallo[/color]
> with[color=green]
> > HI*/
> > alert(test_string)
> > //--></script>
> >
> > For an overview of the javascript methods that deal with regular[/color]
> expressions[color=green]
> > (NOT the best summary available online of course! just one among many
> > others!):
> > http://www.unitedscripters.com/spellbinder/regexp.html
> >
> > I hope this helps
> > ciao
> > Alberto
> > http://www.unitedscripters.com/
> >
> >
> >
> >
> >
> >
> > "Harry" <harald.humml@t-systems.at> ha scritto nel messaggio
> > news:b3271585.0408160815.4ef7c45@posting.google.co m...[color=darkred]
> > > Hi there,
> > >
> > > does anyone know how I can build a regular expression e.g. for the
> > > string.search() function on runtime, depending on the content of
> > > variables? Should be something like this:
> > >
> > > var strkey = "something";
> > > var str = "Somethin like this";
> > >
> > > if( str.search( / + strkey + / ) > -1 )
> > > {
> > > ...
> > > }
> > >
> > > TIA
> > > Harry[/color]
> >
> >[/color][/color]
Evertjan.
Guest
  
Posts: n/a
#6: Jul 23 '05

re: How to build a regular expression on runtime?

Harry wrote on 17 aug 2004 in comp.lang.javascript:
[color=blue]
> In this example, the problem is that the searchstring is hardcoded.
> What I want is:
>
> var somestringarray = new Array( "one", "two", "three" );
> var somestring = "This is one of my favorite";
> for( var i = 0; i < somestringarray.length; i++ )
> {
> if( somestring.search( somestringarray[ i ] ) > -1 )
> {
> ...
> break;
> }
>[/color]

re = new RegExp(somestringarray[i],"i")
if (somestring.search(re)>=0)

--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)
Thomas 'PointedEars' Lahn
Guest
  
Posts: n/a
#7: Jul 23 '05

re: How to build a regular expression on runtime?

Harry wrote:
[color=blue]
> [...] The Problem is to build a search-regexp dynamically at
> runtime. Naturally I will search with regexp like this:
>
> var somestring = "somecontent";
> if( somestring.search( /some/ ) > -1 )
> {
> ...
> }
>
> In this example, the problem is that the searchstring is hardcoded.
> What I want is:
>
> var somestringarray = new Array( "one", "two", "three" );
> var somestring = "This is one of my favorite";
> for( var i = 0; i < somestringarray.length; i++ )
> {
> if( somestring.search( somestringarray[ i ] ) > -1 )
> {
> ...
> break;
> }
> }
>
> How can I achieve this?[/color]

if (new RegExp(somestringarray[i]).test(somestring))
{
...
}

You should be aware that Regular Expressions may contain special characters
(".", "?" etc.) You must escape them in somestringarray[i] prior if they
should not have their special meaning, i.e. you must work on a ruleset of
RegExps allowed for your users. If no RegExp at all is allowed for input,
use the escapeRE() method I posted a few days before.

And if you do not search for patterns, but only for strings, you should use
String.prototype.indexOf() instead, not requiring any RegExp object, which
is usually faster.
[color=blue]
> [Top post][/color]

Please don't, see the <http://jibbering.com/faq/>.


PointedEars

P.S.: de.comp.lang.javascript exists.
--
Let's introduce General Protection to Corporal Punishment
Alberto
Guest
  
Posts: n/a
#8: Jul 23 '05

re: How to build a regular expression on runtime?

Hello

it doesn't matter whether you want to replace or search: what you basically
need is to compile a regular expression on the run, ISN'T IT?
Try the code I sent to you:

<script><!--
var test_string="hallo guy hallo! I said hallo!";
var yourRegExp_as_text="\\w{5}"; //that checks for 5 letters long words
var regExpObject=new RegExp();
//now use the built in method compile
regExpObject.compile(yourRegExp_as_text, "gi");
/*the second argument takes in the so called modifiers. g stands fopr GLOBAL
scope (search ALL the occurrencies, that is), i stands for case INsensitive
search*/

//Now you have a valid regular expression
/*use it with methods that are regular expression methods, instance
replace():*/
test_string=test_string.replace(regExpObject, "HI"); /*replaced hallo with
HI*/
alert(test_string)
//--></script>

Once you don't need replacing, that's not a problem, you can use search:
test_string.seRCH(regExpObject);

You'd have to work a bit yourself on the codes sent as a reply.
Anyway, to get closer to your needs:

<script><!--
var somestringarray = new Array( "one", "two", "three" );
var somestring = "This is one of my favorite";
var regExpObject=new RegExp();
for( var i = 0; i < somestringarray.length; i++ )
{
regExpObject.compile(somestringarray[i], "gi");
if( somestring.match( regExpObject ))
{alert(somestringarray[i])
break;
}
}
//--></script>

ciao
Alberto
http://www.unitedscripters.com/
Harry
Guest
  
Posts: n/a
#9: Jul 23 '05

re: How to build a regular expression on runtime?

Hi,

Ok, I´ve it now. Thank you all for the helpful replies. Great forum!

Harry



"Alberto" <nospam@nospam.nospam> wrote in message news:<FmqUc.148822$5D1.7342145@news4.tin.it>...[color=blue]
> Hello
>
> it doesn't matter whether you want to replace or search: what you basically
> need is to compile a regular expression on the run, ISN'T IT?
> Try the code I sent to you:
>
> <script><!--
> var test_string="hallo guy hallo! I said hallo!";
> var yourRegExp_as_text="\\w{5}"; //that checks for 5 letters long words
> var regExpObject=new RegExp();
> //now use the built in method compile
> regExpObject.compile(yourRegExp_as_text, "gi");
> /*the second argument takes in the so called modifiers. g stands fopr GLOBAL
> scope (search ALL the occurrencies, that is), i stands for case INsensitive
> search*/
>
> //Now you have a valid regular expression
> /*use it with methods that are regular expression methods, instance
> replace():*/
> test_string=test_string.replace(regExpObject, "HI"); /*replaced hallo with
> HI*/
> alert(test_string)
> //--></script>
>
> Once you don't need replacing, that's not a problem, you can use search:
> test_string.seRCH(regExpObject);
>
> You'd have to work a bit yourself on the codes sent as a reply.
> Anyway, to get closer to your needs:
>
> <script><!--
> var somestringarray = new Array( "one", "two", "three" );
> var somestring = "This is one of my favorite";
> var regExpObject=new RegExp();
> for( var i = 0; i < somestringarray.length; i++ )
> {
> regExpObject.compile(somestringarray[i], "gi");
> if( somestring.match( regExpObject ))
> {alert(somestringarray[i])
> break;
> }
> }
> //--></script>
>
> ciao
> Alberto
> http://www.unitedscripters.com/[/color]
Alberto
Guest
  
Posts: n/a
#10: Jul 23 '05

re: How to build a regular expression on runtime?

You're very welcome. Happy tho have been helpful.

ciao
Alberto
http://www.unitedscripters.com/


"Harry" <harald.humml@t-systems.at> ha scritto nel messaggio
news:b3271585.0408180347.6642c09a@posting.google.c om...[color=blue]
> Hi,
>
> Ok, I´ve it now. Thank you all for the helpful replies. Great forum!
>
> Harry
>
>
>
> "Alberto" <nospam@nospam.nospam> wrote in message[/color]
news:<FmqUc.148822$5D1.7342145@news4.tin.it>...[color=blue][color=green]
> > Hello
> >
> > it doesn't matter whether you want to replace or search: what you[/color][/color]
basically[color=blue][color=green]
> > need is to compile a regular expression on the run, ISN'T IT?
> > Try the code I sent to you:
> >
> > <script><!--
> > var test_string="hallo guy hallo! I said hallo!";
> > var yourRegExp_as_text="\\w{5}"; //that checks for 5 letters long words
> > var regExpObject=new RegExp();
> > //now use the built in method compile
> > regExpObject.compile(yourRegExp_as_text, "gi");
> > /*the second argument takes in the so called modifiers. g stands fopr[/color][/color]
GLOBAL[color=blue][color=green]
> > scope (search ALL the occurrencies, that is), i stands for case[/color][/color]
INsensitive[color=blue][color=green]
> > search*/
> >
> > //Now you have a valid regular expression
> > /*use it with methods that are regular expression methods, instance
> > replace():*/
> > test_string=test_string.replace(regExpObject, "HI"); /*replaced hallo[/color][/color]
with[color=blue][color=green]
> > HI*/
> > alert(test_string)
> > //--></script>
> >
> > Once you don't need replacing, that's not a problem, you can use search:
> > test_string.seRCH(regExpObject);
> >
> > You'd have to work a bit yourself on the codes sent as a reply.
> > Anyway, to get closer to your needs:
> >
> > <script><!--
> > var somestringarray = new Array( "one", "two", "three" );
> > var somestring = "This is one of my favorite";
> > var regExpObject=new RegExp();
> > for( var i = 0; i < somestringarray.length; i++ )
> > {
> > regExpObject.compile(somestringarray[i], "gi");
> > if( somestring.match( regExpObject ))
> > {alert(somestringarray[i])
> > break;
> > }
> > }
> > //--></script>
> >
> > ciao
> > Alberto
> > http://www.unitedscripters.com/[/color][/color]
Closed Thread

« previous question | next question »

/bytes/development

/bytes/it

Forums
Visit our community forums for general discussions and latest on Bytes

Our staff and community areas have moved to bytes.com/forums/

/bytes/about

We are a network of experts and professionals in IT and software development that help one another with answers to tough questions and share insights. Get the best answers to your questions from over 226,537 network members.

dev questions:
algorithms | asp | asp.net | c/c++ | coldfusion | c# | flash | html/css | java | javascript |
mobile dev | .net | perl | php | python | ruby | software dev | vb.net | visual basic | xml
it questions:
access | apache | careers | db2 | iis | macosx | mysql | networking | oracle | postgresql | sql server | unix | windows

About Bytes | Copyright 1995-2009 BYTES. All rights Reserved