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sed replace command

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# 1  
Old 01-13-2017
sed replace command
Hi.

I need to append/prefix an & character to every 'single' & character (not when there are 2 or more grouped together) I find in a file. I can do it using this cmd:
Code:
cat ${file} | sed -e 's/&/&&/g' > ${new_file}

How can I modify this to ensure I only replace single &'s and not operate on multiple groupings like && or &&& etc.?

Many thanks.
Last edited by rbatte1; 01-13-2017 at 09:45 AM.. Reason: Added ICODE tags
# 2  
Old 01-13-2017
Try
Code:
sed 's/\([^&]\)\(&\)\([^&]\)/\1\2\2\3/g' file

# 3  
Old 01-13-2017
Thanks Rudi. It only seems to partially work for me. looks like it only updates single &s if they're on a line with other &s.
Here's the output:

Code:
[oracle@xtest54 bin]$ cat test1
&

&

&&

&&&

& & &
&& && &&&&&&
[oracle@xtest-54 bin]$ sed 's/\([^&]\)\(&\)\([^&]\)/\1\2\2\3/g' test1
&

&

&&

&&&

& && &
&& && &&&&&&
[oracle@xtest-54 bin]$

# 4  
Old 01-13-2017
Had you posted a meaningful input sample, a better solution could have been offered. Try
Code:
sed ':L; s/\(^\|[^&]\)\(&\)\([^&]\|$\)/\1\2\2\3/g; tL' file
&&

&&

&&

&&&

&& && &&
&& && &&&&&&

This User Gave Thanks to RudiC For This Post:
user052009
# 5  
Old 01-13-2017
Perfect. Yes, I should've added an example to be clear. Sorry for that and thanks for the solution.
# 6  
Old 01-13-2017
I find sed scripts with a lot of escapes much more readable if other separator is used.


Same code Rudi posted is much more readable and does the same :
Code:
sed ':L; s#\(^\|[^&]\)\(&\)\([^&]\|$\)#\1\2\2\3#g; tL'

In this case it's hash, but it can be anything but the patterns required for transformation.
These 2 Users Gave Thanks to Peasant For This Post:
rbatte1 user052009
# 7  
Old 01-13-2017
With perl's lookbehind and lookahead:
Code:
perl -pe 's/(?<!&)&(?!&)/&&/g' file

This User Gave Thanks to MadeInGermany For This Post:
Scrutinizer
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