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How to print the extended regular expression ?

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Top Forums Shell Programming and Scripting How to print the extended regular expression ?
# 1  
Old 09-01-2011
How to print the extended regular expression ?
Hello,
How to print the field separator in awk? please see the following code:
cat a.txt
Code:
a 1s  2s   3s     4s
b  2s    4s

Code:
[river@localhost Desktop]$ awk  'BEGIN{FS==" "} {print $2 $3 }' te 
1s2s
2s4s

I want to get the following output :
Code:
1s  2s
2s    4s

How to realize this ?

Code:
[river@localhost Desktop]$ cat te
a 1s,,2s   3s     4s
b  2s    4s
[river@localhost Desktop]$ awk  'BEGIN{ FS = "[,| ]" } {print $2 $3 }' te 
1s
2s
[river@localhost Desktop]$

I want to get the following result:
Code:
1s,,2s
2s    4s

How to realize it ?
Last edited by 915086731; 09-01-2011 at 04:10 AM..
# 2  
Old 09-01-2011
There is OFS - output field separator in awk. Either change it in BEGIN block, or add FS manually:
Code:
{print $1 FS $2}

# 3  
Old 09-01-2011
However ,
Code:
{print $1 FS $2}

I get the following :
Code:
[river@localhost Desktop]$ awk  ' {print $2 FS  $3 }' te 
1s,,2s 3s                               
2s 4s                                     !!only one space
[river@localhost Desktop]$

In origin file, the content between "2s" and "4s" is 4 spaces, but it only print 1 space.
and I need to specify FS to be "," or " ".
# 4  
Old 09-01-2011
Adjacent characters will be threaded as multiple field separators.

When FS=",", a,,b will be interpreted as a null b.


It would be easy with Perl:

Code:
% cat infile 
a 1s,,2s   3s     4s
b  2s    4s
% perl -nle'
  print +(split /\s(?!\s)/)[1,2]
  ' infile
1s,,2s  3s    
2s   4s

# 5  
Old 09-01-2011
Oh, sorry, I decide not to use perl, thanks.
# 6  
Old 09-01-2011
Why not Perl?

Which operating system and awk version are you using?
# 7  
Old 09-01-2011
I am using fedora 15 , bash environment.
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