Regular expression to exclude lines?

[Shannon Jacobs]

Sorry to ask what is surely a trivial question. Also sorry that I don't have
my current code version on hand, but... Anyway, must be some problem with
trying to do the negative. It seems like I get into these ruts each time I
try to deal with regular expressions.

All I'm trying to do is delete the lines which don't contain a particular
string. Actually a filter to edit a log file. I can find and replace a thing
with null, but can't figure out how to find the lines which do not contain
the thing.

Going further, I want to generalize and use a JavaScript variable containing
the decision string, but first I need to worry about the not-within-a-line
problem.

[Thomas 'PointedEars' Lahn]

Shannon Jacobs wrote:

Sorry to ask what is surely a trivial question.
Hm, I don't think it is this trivial.
All I'm trying to do is delete the lines which don't contain a
particular string. Actually a filter to edit a log file. I can
find and replace a thing with null, but can't figure out how to
find the lines which do not contain the thing.

Here's a quickhack that filters out of three lines the one that
does not contain the word `line':

alert("this is a line\nthis is a\nthis is a
line".match(/\n*[^\n]*\n*([^\n]*[^l][^i][^n][^e][^\n]*\n)*[^\n]*\n*/)[1])

But there must be a better a better way, IIRC there is something
called `negative lookahead', supported from JavaScript 1.5 on,
which I have yet not worked with.
PointedEars

[Lasse Reichstein Nielsen]

Thomas 'PointedEars' Lahn <Po*********@we b.de> writes:

Shannon Jacobs wrote:

Sorry to ask what is surely a trivial question.
Hm, I don't think it is this trivial.

Neither do I. Negative matches in regular expressions rarely are.
Here's a quickhack that filters out of three lines the one that
does not contain the word `line':

alert("this is a line\nthis is a\nthis is a
line".match(/\n*[^\n]*\n*([^\n]*[^l][^i][^n][^e][^\n]*\n)*[^\n]*\n*/)[1])
That's purely accidental. If you add a line in front, e.g.,
"bad thing\nthis is a line\nthis is a\n this is a line", it matches
the string containing the second and third line.
But there must be a better a better way, IIRC there is something
called `negative lookahead', supported from JavaScript 1.5 on,
which I have yet not worked with.

Negative lookahead might be an easier way to do it.

The hard way:

/^([^l\n]*(l[^i]|li[^n]|lin[^e]))*([^l\n])*$/m
(any "l" is not followed by "ine")

With negative lookahead:
/^([^l\n]*l(?!ine))*[^l\n]*$/m

The "m" at the end makes "^" and "$" match beginning/end of line.

These regexps only check for the letters "line", not whether they
occur as a word. To do that, one must check for word boundaries around it:

Hard:
/^([^l\n]*(\bl([^i]|i[^n]|in[^e]|ine\B)|\Bl))*[^l\n]*$/m
Easy:
/^([^l\n]*(\bl(?!ine\b)| \Bl))*[^l\n]*$/m

Any "l" right after a word boundary is not followed by ine+word boundary.

To test this regexp, try:
---
var regexp = /^([^l\n]*(\bl(?!ine\b)| \Bl))*[^l\n]*$/mg ;
var lines = "nonline\nline\ nlinefeed\nwith line in the middle\n"+
"no l-word here\n\npreviou s l-word was empty\nand ending in line";
var dellines = lines.replace(r egexp,"---DELETED---");
alert(lines);
alert(dellines) ;
---
A longer explanation of:
/^([^l\n]*(\bl(?!ine\b)| \Bl))*[^l\n]*$/m
^ beginning of line
^ some non-l/non-newlines
^ either wordboundary + l not followed by "ine"+wordbound ary
^or l not after word boundary
^any number of times
^ and then some non-l/non-newlines again.

Good luck:)
/L
--
Lasse Reichstein Nielsen - lr*@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'

[Evertjan.]

Lasse Reichstein Nielsen wrote on 24 nov 2003 in comp.lang.javas cript:

Negative lookahead might be an easier way to do it.

What about this non greedy "*?" form:

<script>

function replLine(x,t){
t+="\n"
var re = new RegExp("[^\n]*?"+x+"[^\n]*\n","g");
t = t.replace(re ,"")
return t.replace(/\n$/,"")
}

tx="bad thing\nthis is a line\nthis is a\n this is a line"

alert(replLine( "thing",tx) )
alert(replLine( "line",tx))

</script>


--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

[Evertjan.]

Evertjan. wrote on 24 nov 2003 in comp.lang.javas cript:

Lasse Reichstein Nielsen wrote on 24 nov 2003 in comp.lang.javas cript:

Negative lookahead might be an easier way to do it.

What about this non greedy "*?" form:

<script>

function replLine(x,t){
t+="\n"
var re = new RegExp("[^\n]*?"+x+"[^\n]*\n","g");
t = t.replace(re ,"")
return t.replace(/\n$/,"")
}

tx="bad thing\nthis is a line\nthis is a\n this is a line"

alert(replLine( "thing",tx) )
alert(replLine( "line",tx))

</script>

"All I'm trying to do is delete the lines which don't contain a
particular string. "

Wow, I missed the "n't"

I will try again later.

--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

[Evertjan.]

Evertjan. wrote on 24 nov 2003 in comp.lang.javas cript:

"All I'm trying to do is delete the lines which don't contain a
particular string. "

Wow, I missed the "n't"

I will try again later.

This better?

<script>

function replLine(x,t){
var re = new RegExp(x,"");
t+="\n"
t = t.replace(
/.*?\n/g,
function($0,$1, $2)
{return (!re.test($0))? $0:""}
)
return t.replace(/\n$/,"")
}

tx="bad thing\nthis is a line\nthis is a\n this is a line"

alert(replLine( "thing",tx) )
alert(replLine( "line",tx))

</script>

--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

[Evertjan.]

Evertjan. wrote on 24 nov 2003 in comp.lang.javas cript:

Evertjan. wrote on 24 nov 2003 in comp.lang.javas cript:

"All I'm trying to do is delete the lines which don't contain a
particular string. "

Wow, I missed the "n't"

I will try again later.

This better?

<script>

function replLine(x,t){
var re = new RegExp(x,"");
t+="\n"
t = t.replace(
/.*?\n/g,
function($0,$1, $2)
{return (!re.test($0))? $0:""}
)
return t.replace(/\n$/,"")
}

tx="bad thing\nthis is a line\nthis is a\n this is a line"

alert(replLine( "thing",tx) )
alert(replLine( "line",tx))

</script>

Monologue follows.

Damn, forgot to remove the "!"

<script>

function replLine(x,t){
var re = new RegExp(x,"");
t+="\n"
t = t.replace(
/.*?\n/g,
function($0,$1, $2)
{return (re.test($0))?$ 0:""}
)
return t.replace(/\n$/,"")
}

tx="bad thing\nthis is a line\nthis is a\n this is a line"

alert(replLine( "thing",tx) )
alert(replLine( "line",tx))

</script>

--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

[Lasse Reichstein Nielsen]

"Evertjan." <ex************ **@interxnl.net > writes:

Evertjan. wrote on 24 nov 2003 in comp.lang.javas cript:

This better?

Monologue follows.

Damn, forgot to remove the "!" function replLine(x,t){
var re = new RegExp(x,"");
t+="\n"
t = t.replace(
/.*?\n/g,
function($0,$1, $2)
{return (re.test($0))?$ 0:""}
)
return t.replace(/\n$/,"")
}

This first splits the string into lines, and then replaces each line
based on a second test.
It should work (and seems to).

I don't think you need a non-greedy match (.*?) since . doesn't match
a newline character.
Maybe you can get around adding the extra "\n" by using multiline
matching: /^.*$/gm,
It doesn't remove the newlines in the string though. None of my
attempts have done that so far.

This method uses several regexp matches, not just one (which is
sometimes the better approach :), but the first is really just
splitting into lines. You can use the split method for that.

How about this:

// returns new array containing only those elements that match re
Array.prototype .filter = function filter(re) {
var res = [];
for (var i=0;i<this.leng th;i++) {
if (re.test(this[i])) {res.push(this[i]);}
}
return res;
}

var tx="bad thing\nthis is a line\nthis is a\n this is a line";
alert(tx.split( "\n").filte r(/line/).join("\n"));

Sadly, adding properties to Array.prototype means that you can't
(easily) use
for (var i in this)
to iterate through a sparse array. The filter method is enumerable,
so it is also included.

/L
--
Lasse Reichstein Nielsen - lr*@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'

[Evertjan.]

Lasse Reichstein Nielsen wrote on 24 nov 2003 in comp.lang.javas cript:

I don't think you need a non-greedy match (.*?) since . doesn't match
a newline character.

True !

--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

[Dr John Stockton]

JRS: In article <3F************ **@PointedEars. de>, seen in
news:comp.lang. javascript, Thomas 'PointedEars' Lahn
<Po*********@we b.de> posted at Mon, 24 Nov 2003 16:39:25 :-

Shannon Jacobs wrote:

Sorry to ask what is surely a trivial question.

Hm, I don't think it is this trivial.

All I'm trying to do is delete the lines which don't contain a
particular string. Actually a filter to edit a log file. I can
find and replace a thing with null, but can't figure out how to
find the lines which do not contain the thing.

Here's a quickhack that filters out of three lines the one that
does not contain the word `line':

alert("this is a line\nthis is a\nthis is a
line".match(/\n*[^\n]*\n*([^\n]*[^l][^i][^n][^e][^\n]*\n)*[^\n]*\n*/)[1])

But there must be a better a better way, IIRC there is something
called `negative lookahead', supported from JavaScript 1.5 on,
which I have yet not worked with.

AIUI, the OP wants a file which is the previous file minus those lines
which do not contain the string. That code, after broken-string
correction, pops up a box showing the first unwanted line.

Javascript "alone" is not capable of file handling, AFAICS.

If the OP can read and write the file line by line, controlled by
javascript, and apply script to each line, then it is only necessary to
do (pseudo-code follows)

while not EoF(FI) do begin Readln(FI, S) ; // pascal
if ( ! /«string»/.test(S) ) continue // javascript
Writeln(FO, S) end ; // pascal


The OP has MSOE, which suggests Windows. If the job is to be run in
DOS, Windows, or UNIX, then the task is trivial using MiniTrue, which
IMHO is a most valuable tool. Example :

mtr -no~ jt.htm - e

will put, on standard output, all those lines of jt.htm which do not
contain the letter e. A RegExp can be used for the search, in place
of e. There may be a way of doing it without using standard output.

--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 MIME. ©
Web <URL:http://www.merlyn.demo n.co.uk/> - FAQish topics, acronyms, & links.
I find MiniTrue useful for viewing/searching/altering files, at a DOS prompt;
free, DOS/Win/UNIX, <URL:http://www.idiotsdelig ht.net/minitrue/> Update soon?