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Regular Expression In Sed

 
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# 1  
Old 05-12-2011
Regular Expression In Sed
Hi ,
I am learing sed

Code:
 echo  abc 123 def 456  |  sed 's|\([a-z]*\) \([0-9]*\)|\1|'

is returning
Code:
abc def 456

i was hoping
Code:
abc def

"\1" should only print the occurence of the first pattern
but according to my understanding it is just removing the first occurence of the second pattern Smilie

Please can some onle explain what's really happing here and if i want to get only first patternt using "\( \)" how to achieve that
# 2  
Old 05-12-2011
sed's s command only hits the first match unless you add a g flag:

Code:
$ echo  abc 123 def 456  |  sed 's|\([a-z]*\) \([0-9]*\)|\1|'
abc def 456
$ echo  abc 123 def 456  |  sed 's|\([a-z]*\) \([0-9]*\)|\1|g'
abcdef
$

This User Gave Thanks to Perderabo For This Post:
max_hammer
# 3  
Old 05-12-2011
Quote:
Originally Posted by Perderabo
sed's s command only hits the first match unless you add a g flag:
Only partially true :
... Or until you specify another match number ...

Code:
# echo 'ABCDEFG'
ABCDEFG
# echo 'ABCDEFG' | sed 's/././'
.BCDEFG
# echo 'ABCDEFG' | sed 's/././1'
.BCDEFG
# echo 'ABCDEFG' | sed 's/././2'
A.CDEFG
# echo 'ABCDEFG' | sed 's/././3'
AB.DEFG
# echo 'ABCDEFG' | sed 's/././5'
ABCD.FG
# echo 'ABCDEFG' | sed 's/././g'
.......
#

---------- Post updated at 09:48 PM ---------- Previous update was at 09:36 PM ----------

Regarding your case, i would suggest you target the unwanted pattern and delete it (substitute it with empty string)
Code:
# echo  abc 123 def 456  | sed 's/ [0-9][0-9]*//g'
abc def

This User Gave Thanks to ctsgnb For This Post:
max_hammer
# 4  
Old 05-13-2011
Quote:
Originally Posted by Perderabo
sed's s command only hits the first match unless you add a g flag:
Code:
$ echo  abc 123 def 456  |  sed 's|\([a-z]*\) \([0-9]*\)|\1|'
abc def 456

This is really incredible Smilie, I thought it would print 'abc 123 def' omitting '456' for the \1, because of the greedy matching nature of sed's regular expression. This is really a new thing I learnt today..
# 5  
Old 05-13-2011
Thank you Perderabo and ctsgnb now the things are clear to me
# 6  
Old 05-13-2011
Code:
# echo  abc 123 def 456  |  sed 's|\([a-z]*\) \([0-9]*\)|\1|'
abc def 456
# echo  abc 123 def 456  |  sed 's|\([a-z]*\) \([0-9]*\)|\1|2'
abc 123 def
# echo  abc 123 def 456  |  sed 's|\([a-z]*\) \([0-9]*\)|\1|g'
abc def

# 7  
Old 05-13-2011
Quote:
Originally Posted by ctsgnb
Code:
# echo  abc 123 def 456  |  sed 's|\([a-z]*\) \([0-9]*\)|\1|2'
abc 123 def
# echo  abc 123 def 456  |  sed 's|\([a-z]*\) \([0-9]*\)|\1|g'
abc def

But, I am getting different ouput on GNU sed version 4.1.5
Code:
echo abc 123 def 456 | sed 's|\([a-z]*\) \([0-9]*\)|\1|2'

# Ans: abc 123def 456
 
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