Re: Regular expression: option match after a greedy/non-greedy match
When i run this script i get following Error
bash-4.2$ ./regex.pl
feature version v5.16.0 required--this is only version v1.160.0 at ./
regex.pl line 4.
BEGIN failed--compilation aborted at ./regex.pl line 4.
But I am using perl version as swon below.
bash-4.2$ perl -v
This is perl 5, version 16, subversion 3 (v5.16.3) built for i686-linux
Copyright 1987-2012, Larry Wall
Perl may be copied only under the terms of either the Artistic License or
the
GNU General Public License, which may be found in the Perl 5 source kit.
Complete documentation for Perl, including FAQ lists, should be found on
this system using man perl or perldoc perl. If you have access to the
Internet, point your browser at http://www.perl.org/, the Perl Home Page.
On Wed, Sep 17, 2014 at 8:52 AM, Jing Yu logus...@googlemail.com wrote:
Hi Viet-Duc Le,
On 17 Sep 2014, at 10:23, Viet-Duc Le leviet...@kaist.ac.kr wrote:
Greeting from S. Korea !
I am parsing the output of ffmpeg with perl. Particular, I want to print
only
these lines among the output and capturing the resolution, i.e. 1280x720.
Stream #0:0: Video: h264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98
fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
Stream #0:1(jpn): Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
Stream #0:2(eng): Subtitle: ass (default)
.
My code is following:
# INFO is pipe to ffmpeg
# Here, the print $1 $2 $3 $4\n is for debugging .
while ( INFO ) {
if ( regular expression ) {
print $1 $2 $3 $4\n;
}
}
Desirable outputs:
- Video 1280 720
Audio
Subtitle
Regarding the regular expession:
1. /Stream #\d:\d.*(Video|Audio|Subtitle).*(\d+)x(\d+)/ (greedy)
- Video 0 720
Q: why does $2 give 0? I remember .* match backward starting from the end of
the string. Then it should be Video 1280 720 as output.
that '0' is from 128'0', since the '.*' consumes 128. What it does under
the hood is .* first will reach to the end of the target string, and then
backtract according to the following regex. Once the whole regex is
satisfied, it will stop backtracting, although further retracting will
possibly also satisfy the regex.
2. /Stream #\d:\d.*(Video|Audio|Subtitle).*?(\d+)x(\d+)/ (non greedy)
- Video 1280 720
Q: I can understand this, but again I think (1) should work too.
3. /Stream #\d:\d.*(Video|Audio|Subtitle).*?(?:(\d+)x(\d+))?/ ( non-capturing
optional group )
- Video
Audio
Subtitle
Q: It seems that the resolution part
is ignored because it is optional. Otherwise, the output will contains
Video only as (1) and (2). How can I circumvent this ?
that ?: prevents $ variables to capture the matching regex group. I guess
you can get rid of it. The trailing ? already tells the regex group to
match optionally. It is equivalent to {0,1}. The big problem coming with it
is the middle .*?. Since the last part is optional, .*? will just match the
least number of char possible, which is nothing.
4. /Stream #\d:\d.*(Video|Audio|Subtitle).+?(?:(\d+)x(\d+))?.*?$/
- Video
Audio
Subtitle
Q: I tried to match things after the resolution, hoping that it will be
captured.
Again the ?: prevents it being captured. .+? in the middle is better, now
it matches ':'.
5. /Stream #\d:\d.*(Video|Audio|Subtitle).+?(?:(\d+)x(\d+))?(.*?)$/ ( let's
capture the last part)
- Videoh264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98 fps,
23.98 tbr, 1k tbn, 47.95 tbc (default)
Audioac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
Subtitleass (default)
Q: Now $2 and $3 is undef, and the rest of the string went to $4. Again, I am
quite puzzled by the output.
If it is optional, it is non greedy. So everything goes to the (.*?)$.
Please pardon my long email. I hope someone can point out the flaws in my
logic.
Here, I can match and print Video/Audio/Subtitle separately.
But I wish for one expression to match them all, one expression to print
them.
In general, it is a better practise to add 'x' to your regex to make it
more readable. My regex might not be the best, but it works as expected.
use strict;
use warnings;
use 5.16.0;
while(DATA){
/ (Video|Audio|Subtitle) (?: (?:.) +? (\d+x\d+) || (?:.)+ ) /x
and say $1, $2, $3, $4;
}
__DATA__
Stream #0:0: Video: h264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9,
23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
Stream #0:1(jpn): Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
Stream #0:2(eng): Subtitle: ass (default)
The '||' operator will first check the group before it. It will only look
at the other group if the first group fails. This puts your resolution
group matching as priority, but not necessity.
Hope this helps.
Jing
--
*
Don't ask them WHY they hurt you,
because all they'll tell you is lies and excuses.
Just know they were wrong, and try to move
Re: Regular expression: option match after a greedy/non-greedy match
On 17 Sep 2014, at 17:08, Uday Vernekar vernekaru...@gmail.com wrote: When i run this script i get following Error bash-4.2$ ./regex.pl feature version v5.16.0 required--this is only version v1.160.0 at ./regex.pl line 4. BEGIN failed--compilation aborted at ./regex.pl line 4. But I am using perl version as swon below. bash-4.2$ perl -v This is perl 5, version 16, subversion 3 (v5.16.3) built for i686-linux Copyright 1987-2012, Larry Wall Perl may be copied only under the terms of either the Artistic License or the GNU General Public License, which may be found in the Perl 5 source kit. Complete documentation for Perl, including FAQ lists, should be found on this system using man perl or perldoc perl. If you have access to the Internet, point your browser at http://www.perl.org/, the Perl Home Page. Strange... I only used 5.16.0 for the feature 'say'. You can of course omit that part and change 'say' to 'print', and hang a \n at the end instead. Cheers, Jing
Re: Regular expression: option match after a greedy/non-greedy match
when i change
use 5.16.0; to use feature ':5.10';
it works i get following output
bash-4.2$ ./regex.pl
Use of uninitialized value $3 in say at ./regex.pl line 7, DATA line 1.
Use of uninitialized value $4 in say at ./regex.pl line 7, DATA line 1.
Video1280x720
Use of uninitialized value $2 in say at ./regex.pl line 7, DATA line 2.
Use of uninitialized value $3 in say at ./regex.pl line 7, DATA line 2.
Use of uninitialized value $4 in say at ./regex.pl line 7, DATA line 2.
Audio
Use of uninitialized value $2 in say at ./regex.pl line 7, DATA line 3.
Use of uninitialized value $3 in say at ./regex.pl line 7, DATA line 3.
Use of uninitialized value $4 in say at ./regex.pl line 7, DATA line 3.
Subtitle
how these two use statements differ.
use 5.16.0;
perl regex.pl works
why ./regex.pl doesnt work.
it gives following error
feature version v5.16.0 required--this is only version v1.160.0 at ./
regex.pl line 4.
BEGIN failed--compilation aborted at ./regex.pl line 4.
On Wed, Sep 17, 2014 at 2:38 PM, Uday Vernekar vernekaru...@gmail.com
wrote:
When i run this script i get following Error
bash-4.2$ ./regex.pl
feature version v5.16.0 required--this is only version v1.160.0 at ./
regex.pl line 4.
BEGIN failed--compilation aborted at ./regex.pl line 4.
But I am using perl version as swon below.
bash-4.2$ perl -v
This is perl 5, version 16, subversion 3 (v5.16.3) built for i686-linux
Copyright 1987-2012, Larry Wall
Perl may be copied only under the terms of either the Artistic License or
the
GNU General Public License, which may be found in the Perl 5 source kit.
Complete documentation for Perl, including FAQ lists, should be found on
this system using man perl or perldoc perl. If you have access to the
Internet, point your browser at http://www.perl.org/, the Perl Home Page.
On Wed, Sep 17, 2014 at 8:52 AM, Jing Yu logus...@googlemail.com wrote:
Hi Viet-Duc Le,
On 17 Sep 2014, at 10:23, Viet-Duc Le leviet...@kaist.ac.kr wrote:
Greeting from S. Korea !
I am parsing the output of ffmpeg with perl. Particular, I want to print
only
these lines among the output and capturing the resolution, i.e. 1280x720.
Stream #0:0: Video: h264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98
fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
Stream #0:1(jpn): Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
Stream #0:2(eng): Subtitle: ass (default)
.
My code is following:
# INFO is pipe to ffmpeg
# Here, the print $1 $2 $3 $4\n is for debugging .
while ( INFO ) {
if ( regular expression ) {
print $1 $2 $3 $4\n;
}
}
Desirable outputs:
- Video 1280 720
Audio
Subtitle
Regarding the regular expession:
1. /Stream #\d:\d.*(Video|Audio|Subtitle).*(\d+)x(\d+)/ (greedy)
- Video 0 720
Q: why does $2 give 0? I remember .* match backward starting from the end
of the string. Then it should be Video 1280 720 as output.
that '0' is from 128'0', since the '.*' consumes 128. What it does under
the hood is .* first will reach to the end of the target string, and then
backtract according to the following regex. Once the whole regex is
satisfied, it will stop backtracting, although further retracting will
possibly also satisfy the regex.
2. /Stream #\d:\d.*(Video|Audio|Subtitle).*?(\d+)x(\d+)/ (non greedy)
- Video 1280 720
Q: I can understand this, but again I think (1) should work too.
3. /Stream #\d:\d.*(Video|Audio|Subtitle).*?(?:(\d+)x(\d+))?/ (
non-capturing optional group )
- Video
Audio
Subtitle
Q: It seems that the resolution part
is ignored because it is optional. Otherwise, the output will contains
Video only as (1) and (2). How can I circumvent this ?
that ?: prevents $ variables to capture the matching regex group. I guess
you can get rid of it. The trailing ? already tells the regex group to
match optionally. It is equivalent to {0,1}. The big problem coming with it
is the middle .*?. Since the last part is optional, .*? will just match the
least number of char possible, which is nothing.
4. /Stream #\d:\d.*(Video|Audio|Subtitle).+?(?:(\d+)x(\d+))?.*?$/
- Video
Audio
Subtitle
Q: I tried to match things after the resolution, hoping that it will be
captured.
Again the ?: prevents it being captured. .+? in the middle is better, now
it matches ':'.
5. /Stream #\d:\d.*(Video|Audio|Subtitle).+?(?:(\d+)x(\d+))?(.*?)$/ ( let's
capture the last part)
- Videoh264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98 fps,
23.98 tbr, 1k tbn, 47.95 tbc (default)
Audioac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
Subtitleass (default)
Q: Now $2 and $3 is undef, and the rest of the string went to $4. Again, I am
quite puzzled by the output.
If it is optional, it is non greedy. So everything goes to the (.*?)$.
Please pardon my long email. I hope someone can point out the flaws in my
logic.
Here, I can match and print
RE: Re: Regular expression: option match after a greedy/non-greedy match
Dear Jing,
I was confused when I started out the regular expression. Many thanks for the
kind and detailed explanation.
After reading more on perl regex, I think I have a better grasp of the
greedy/non-greedy concept now.
Your code also worked well for my task.
Regards,
Viet-Duc
---Original Message---
From: Jing Yu logus...@googlemail.com
To: Viet-Duc Le leviet...@kaist.ac.kr
Sent date: 2014-09-17 12:20:29 GMT +0900 (Asia/Seoul)
Subject: Re: Regular expression: option match after a greedy/non-greedy match
Hi Viet-Duc Le,
On 17 Sep 2014, at 10:23, Viet-Duc Le leviet...@kaist.ac.kr wrote:
Greeting from S. Korea !
I am parsing the output of ffmpeg with perl. Particular, I want to print only
these lines among the output and capturing the resolution, i.e. 1280x720.
Stream #0:0: Video: h264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98
fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
Stream #0:1(jpn): Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
Stream #0:2(eng): Subtitle: ass (default)
.
My code is following:
# INFO is pipe to ffmpeg
# Here, the print $1 $2 $3 $4\n is for debugging .
while ( INFO ) {
if ( regular expression ) {
print $1 $2 $3 $4\n;
}
}
Desirable outputs:
- Video 1280 720
Audio
Subtitle
Regarding the regular expession:
1. /Stream #\d:\d.*(Video|Audio|Subtitle).*(\d+)x(\d+)/ (greedy)
- Video 0 720
Q: why does $2 give 0? I remember .* match backward starting from the end of
the string. Then it should be Video 1280 720 as output.
that '0' is from 128'0', since the '.*' consumes 128. What it does under the
hood is .* first will reach to the end of the target string, and then backtract
according to the following regex. Once the whole regex is satisfied, it will
stop backtracting, although further retracting will possibly also satisfy the
regex.
2. /Stream #\d:\d.*(Video|Audio|Subtitle).*?(\d+)x(\d+)/ (non greedy)
- Video 1280 720
Q: I can understand this, but again I think (1) should work too.
3. /Stream #\d:\d.*(Video|Audio|Subtitle).*?(?:(\d+)x(\d+))?/ ( non-capturing
optional group )
- Video
Audio
Subtitle
Q: It seems that the resolution part is ignored because it is optional.
Otherwise, the output will contains Video only as (1) and (2). How can I
circumvent this ?
that ?: prevents $ variables to capture the matching regex group. I guess you
can get rid of it. The trailing ? already tells the regex group to match
optionally. It is equivalent to {0,1}. The big problem coming with it is the
middle .*?. Since the last part is optional, .*? will just match the least
number of char possible, which is nothing.
4. /Stream #\d:\d.*(Video|Audio|Subtitle).+?(?:(\d+)x(\d+))?.*?$/
- Video
Audio
Subtitle
Q: I tried to match things after the resolution, hoping that it will be
captured.
Again the ?: prevents it being captured. .+? in the middle is better, now it
matches ':'.
5. /Stream #\d:\d.*(Video|Audio|Subtitle).+?(?:(\d+)x(\d+))?(.*?)$/ ( let's
capture the last part)
- Videoh264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98 fps, 23.98
tbr, 1k tbn, 47.95 tbc (default)
Audioac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
Subtitleass (default)
Q: Now $2 and $3 is undef, and the rest of the string went to $4. Again, I am
quite puzzled by the output.
If it is optional, it is non greedy. So everything goes to the (.*?)$.
Please pardon my long email. I hope someone can point out the flaws in my
logic. Here, I can match and print Video/Audio/Subtitle separately.
But I wish for one expression to match them all, one expression to print them.
In general, it is a better practise to add 'x' to your regex to make it more
readable. My regex might not be the best, but it works as expected.
use strict;use warnings;use 5.16.0;
while(DATA){/ (Video|Audio|Subtitle) (?: (?:.) +? (\d+x\d+) || (?:.)+ )
/xand say $1, $2, $3, $4;}
__DATA__Stream #0:0: Video: h264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9,
23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)Stream #0:1(jpn): Audio: ac3,
48000 Hz, stereo, fltp, 192 kb/s (default)Stream #0:2(eng): Subtitle: ass
(default)
The '||' operator will first check the group before it. It will only look at
the other group if the first group fails. This puts your resolution group
matching as priority, but not necessity.
Hope this helps.Jing
Regular expression: option match after a greedy/non-greedy match
p{margin:0;padding:0;}
Greeting from S. Korea !
I am parsing the output of ffmpeg with perl. Particular, I want to print only
these lines among the output and capturing the resolution, i.e. 1280x720.
Stream #0:0: Video: h264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98
fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
Stream #0:1(jpn): Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
Stream #0:2(eng): Subtitle: ass (default)
.
My code is following:
# INFO is pipe to ffmpeg
# Here, the print $1 $2 $3 $4\n is for debugging .
while ( INFO ) {
if ( regular expression ) {
print $1 $2 $3 $4\n;
}
}
Desirable outputs:
- Video 1280 720
Audio
Subtitle
Regarding the regular expession:
1. /Stream #\d:\d.*(Video|Audio|Subtitle).*(\d+)x(\d+)/ (greedy)
- Video 0 720
Q: why does $2 give 0? I remember .* match backward starting from the end of
the string. Then it should be Video 1280 720 as output.
2. /Stream #\d:\d.*(Video|Audio|Subtitle).*?(\d+)x(\d+)/ (non greedy)
- Video 1280 720
Q: I can understand this, but again I think (1) should work too.
3. /Stream #\d:\d.*(Video|Audio|Subtitle).*?(?:(\d+)x(\d+))?/ ( non-capturing
optional group )
- Video
Audio
Subtitle
Q: It seems that the resolution part is ignored because it is optional.
Otherwise, the output will contains Video only as (1) and (2). How can I
circumvent this ?
4. /Stream #\d:\d.*(Video|Audio|Subtitle).+?(?:(\d+)x(\d+))?.*?$/
- Video
Audio
Subtitle
Q: I tried to match things after the resolution, hoping that it will be
captured.
5. /Stream #\d:\d.*(Video|Audio|Subtitle).+?(?:(\d+)x(\d+))?(.*?)$/ ( let's
capture the last part)
- Videoh264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98 fps, 23.98
tbr, 1k tbn, 47.95 tbc (default)
Audioac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
Subtitleass (default)
Q: Now $2 and $3 is undef, and the rest of the string went to $4. Again, I am
quite puzzled by the output.
Please pardon my long email. I hope someone can point out the flaws in my
logic. Here, I can match and print Video/Audio/Subtitle separately.
But I wish for one expression to match them all, one expression to print them.
Best regards,
Viet-Duc
Re: Regular expression: option match after a greedy/non-greedy match
Hi Viet-Duc Le,
On 17 Sep 2014, at 10:23, Viet-Duc Le leviet...@kaist.ac.kr wrote:
Greeting from S. Korea !
I am parsing the output of ffmpeg with perl. Particular, I want to print only
these lines among the output and capturing the resolution, i.e. 1280x720.
Stream #0:0: Video: h264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98
fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
Stream #0:1(jpn): Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
Stream #0:2(eng): Subtitle: ass (default)
.
My code is following:
# INFO is pipe to ffmpeg
# Here, the print $1 $2 $3 $4\n is for debugging .
while ( INFO ) {
if ( regular expression ) {
print $1 $2 $3 $4\n;
}
}
Desirable outputs:
- Video 1280 720
Audio
Subtitle
Regarding the regular expession:
1. /Stream #\d:\d.*(Video|Audio|Subtitle).*(\d+)x(\d+)/ (greedy)
- Video 0 720
Q: why does $2 give 0? I remember .* match backward starting from the end of
the string. Then it should be Video 1280 720 as output.
that '0' is from 128'0', since the '.*' consumes 128. What it does under the
hood is .* first will reach to the end of the target string, and then backtract
according to the following regex. Once the whole regex is satisfied, it will
stop backtracting, although further retracting will possibly also satisfy the
regex.
2. /Stream #\d:\d.*(Video|Audio|Subtitle).*?(\d+)x(\d+)/ (non greedy)
- Video 1280 720
Q: I can understand this, but again I think (1) should work too.
3. /Stream #\d:\d.*(Video|Audio|Subtitle).*?(?:(\d+)x(\d+))?/ ( non-capturing
optional group )
- Video
Audio
Subtitle
Q: It seems that the resolution part is ignored because it is optional.
Otherwise, the output will contains Video only as (1) and (2). How can I
circumvent this ?
that ?: prevents $ variables to capture the matching regex group. I guess you
can get rid of it. The trailing ? already tells the regex group to match
optionally. It is equivalent to {0,1}. The big problem coming with it is the
middle .*?. Since the last part is optional, .*? will just match the least
number of char possible, which is nothing.
4. /Stream #\d:\d.*(Video|Audio|Subtitle).+?(?:(\d+)x(\d+))?.*?$/
- Video
Audio
Subtitle
Q: I tried to match things after the resolution, hoping that it will be
captured.
Again the ?: prevents it being captured. .+? in the middle is better, now it
matches ':'.
5. /Stream #\d:\d.*(Video|Audio|Subtitle).+?(?:(\d+)x(\d+))?(.*?)$/ ( let's
capture the last part)
- Videoh264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98 fps,
23.98 tbr, 1k tbn, 47.95 tbc (default)
Audioac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
Subtitleass (default)
Q: Now $2 and $3 is undef, and the rest of the string went to $4. Again, I am
quite puzzled by the output.
If it is optional, it is non greedy. So everything goes to the (.*?)$.
Please pardon my long email. I hope someone can point out the flaws in my
logic. Here, I can match and print Video/Audio/Subtitle separately.
But I wish for one expression to match them all, one expression to print
them.
In general, it is a better practise to add 'x' to your regex to make it more
readable. My regex might not be the best, but it works as expected.
use strict;
use warnings;
use 5.16.0;
while(DATA){
/ (Video|Audio|Subtitle) (?: (?:.) +? (\d+x\d+) || (?:.)+ ) /x
and say $1, $2, $3, $4;
}
__DATA__
Stream #0:0: Video: h264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98
fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
Stream #0:1(jpn): Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
Stream #0:2(eng): Subtitle: ass (default)
The '||' operator will first check the group before it. It will only look at
the other group if the first group fails. This puts your resolution group
matching as priority, but not necessity.
Hope this helps.
Jing
