Shell Programming and Scripting

It's the awk range pattern, from Effective AWK Programming:

In the above code it means:

from the record that matches the _2$ pattern to the end of the input (0 -> false -> never -> eof).

And of course, we exit prematurely because of the previous action.

Just a few words about the beauty of the programming code ...
We often try to play golf[1] here and we're doing it for fun.
In my opinion, a piece of code or a program is beautiful when:

- it's self documenting (!)
- concise and simple (simple as possible)
- it takes advantage of the full functionality/potential of the given programming language

That said, at least as far as my posts are concerned, you should take those obfuscated and golfed samples for what they are.
Try to understand them, use them on the command line, but don't use them in scripts and/or production code.
Think about the next maintainer of that code.


1. en.wikipedia.org/wiki/Perl_golf#Perl_golf

Thanks thats good advice about the readability.What prompted me to join this forum is the need to learn to write code that runs as quickly as possible. At work I am now writing tools that run against gigabytes of data written in ksh and nawk. I have been learning to optimise code recently and am astonished by the improvement in speed that can be achieved, particularly when creating extra processes in a loop.One script I optimised recently went from 5+hrs to 20 mins run time simply by minimising the processes being kicked off in two loops!Hence my interest in writing "lean" code....Cheers

Hi danmero,

My input file:
Code:
>sequence_1
ASSSSSSSSSSSDDDDDDDDDDDCCCCCCC
ASDSFDFFDFDFFWERERERERFSDFESFSFD
>sequence_2
ASDFDFDFFDDFFDFDSFDSFDFSDFSDFDSFASDSADSADASD
ASDFFDFDFASFASFASFAFSFFSDASFASFASFAFS
>sequence_3
VEDFGSDGSDGSDGSDGSDGSDGSDG
dDFSDFSDFSDFSDFSDFSDFSDFSDF
SDGFDGSFDGSGSDGSDGSDGSDGSDG
>ABC_6
SAASASASASASASTSDGSDGSDGSDG
dDFSDFSDFSDFSDFSDFSDFSDFSDF
>SDF_7
TASDASDAFSDFSDFSDFSDFSDFSDF
SDGFDGSFDGSGSDGSDGSDGSDGSDG


My desired output file:
Code:
>sequence_2
ASDFDFDFFDDFFDFDSFDSFDFSDFSDFDSFASDSADSADASD
ASDFFDFDFASFASFASFAFSFFSDASFASFASFAFS
>ABC_6
SAASASASASASASTSDGSDGSDGSDG
dDFSDFSDFSDFSDFSDFSDFSDFSDF
>SDF_7
TASDASDAFSDFSDFSDFSDFSDFSDF
SDGFDGSFDGSGSDGSDGSDGSDGSDG

If I got a long list of file, how I can use your script or program to extract only the contents of sequence_2,ABC_6,SDF_7?
Do you have any idea how I can extract specific content only from a long list of file?
As I try, the awk script that you suggested only can extract sequence_2 from a long list of file.
Thanks again

Code:

awk '$1~ /sequence_2|ABC_6|SDF_7/{$1=">"$1;print}' RS=">" ORS="" FS=OFS="\n" file

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Hi, danmero.
I just found out that by using the code that you suggested:

Code:

awk '$1~ /sequence_2|ABC_6|SDF_7/{$1=">"$1;print}' RS=">" ORS="" FS=OFS="\n" file

If my file also got the content header like ABC_61,ABC_605,SDF_750.
All of them, the code that you suggested also will extract.
Do you have any better idea just specific and extract only sequence_2,ABC_6 and SDF_7. Really thanks for your suggestion ^^

Let's try to work around

Code:

awk '$1~">"{f=0}$1~">" && $1~/[sequence_2|ABC_6|SDF_7]$/{f=1}f'  file

seem like it is no work as well