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Multiple substitutions in one expression using sed

 
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# 1  
Old 05-19-2014
Multiple substitutions in one expression using sed
Hi, I'm trying to get multiple substitutions in one expression using sed:

Code:
echo "-foo-_-bar--foo-_bar_-_foo_bar_-foo_-_bar_-" | sed -e "s/[_-|-_|--]/-/g"

So, as you can see I'm trying to replace all instances of _-, -_, -- with - (dash)

I have provided bad example. The question is how to use multiple substitutions in one expression. Post updated.
Last edited by useretail; 05-19-2014 at 05:27 PM.. Reason: updated question
# 2  
Old 05-19-2014
How about something simpler replace all _ with - This gives the result you want:
Code:
echo "--_----__-___-_-__-" | sed -e 's/_/-/g'

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useretail
# 3  
Old 05-19-2014
The question is how to use multiple substitutions in one expression. I just provided bad example.
# 4  
Old 05-19-2014
Try removing the pipe (|) symbols from your sed expression.

Also, if the goal is to have just a line of dashes, you could just globally replace the underscore character.

Code:
echo "--_----__-___-_-__-" | sed 's|_|-|g'
-------------------

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useretail
# 5  
Old 05-19-2014
Standard sed cannot do it like that, you could use 3 separate passes, but it is not the same:
Code:
sed 's/_-/-/g; s/-_/-/g; s/--/-/g' file

But that would not give the same result, since it would also depend on the order of the substitution passes..

With extended regular expressions there you can use alternation, which is provided by BSD sed -E or GNU sed -r
Code:
sed -E 's/_-|-_|--/-/g' file

awk can do it standard:
Code:
awk '{gsub(/_-|-_|--/,"-")}1' file

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# 6  
Old 05-19-2014
Scrutinizer
yeah, first command replaces to the desired result in three passes:
Code:
-foo-bar-foo-bar-foo_bar-foo-bar-

Is it possible to replace to that result using multiple substitutions in one expression?
# 7  
Old 05-19-2014
Yes. Use his awk solution. Most sed versions do not support ERE - what you want. awk does support it. I'm reasonably sure no other sed solution that is a single command and can be generalized with regular expressions. So, No. You cannot do what you ask with sed. Unless you use gnu sed or BSD sed.



ERE == extended regular expressions
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