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Conditional search and delete using SED / Shell script

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# 1  
Old 12-20-2011
Conditional search and delete using SED / Shell script

I want to perform a conditional search and remove my search string.

Input string: "abcdaabcadgfaarstab"
Character to search: "a"
Condition: Remove all "a" in the input string except if it is "aa"
Output string: "bcdaabcdgfaarstb"

Can you please help me in this?
# 2  
Old 12-20-2011
echo "abcdaabcadgfaarstaba" | perl -e '$x=<>; $x=~s/([^a])a([^a])/$1$2/g; $x=~s/^a([^a])|([^a])a$/$1$2/g; print "$x"'

This User Gave Thanks to balajesuri For This Post:
# 3  
Old 12-20-2011
But is there a solution without using perl. Something using sed, awk as we do not have perl in target.
# 4  
Old 12-20-2011
echo "abcdaabcadgfaarstab" | sed 's/\(^\|[^a]\)a\([^a]\|$\)/\1\2/g'

This User Gave Thanks to Ygor For This Post:
# 5  
Old 12-20-2011
@Ygor: I too tried that initially. But it wouldn't work if there was an 'a' at the end, as in "abcdaabcadgfaarstaba". Surprising, but it isn't considering "a" in the end even though the regex has a $.. So, I wrote one to check and substitute separately.

@dominiclajs: Try this:
echo "abcdaabcadgfaarstaba" | sed "s:\([^a]\)a\([^a]\):\1\2:g" | sed "s:^a\([^a]\)\|\([^a]\)a$:\1\2:g"

Last edited by balajesuri; 12-20-2011 at 02:40 AM..
# 6  
Old 12-20-2011
Little tricky .. Smilie
$ echo "abcdaabcadgfaarstab" | sed 's,aa,?,g;s,a,,g;s,?,aa,g'

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