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Eytan
Asked: 2012-05-15 14:33:57 +0800 CST

linux + sed - replace only the right most side char of string

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I have linux machine red-hat 5.1

how to replace only the right single char (most side of string)

example from my sed syntax (not good because its replaced both "a" chars) l

 echo machine1a | sed s'/a/b/g'

 mbchine1b

But the requested answer should be - machine1b and not mbchine1b

linux sed

3 Answers

  1. Best Answer

    You can use the end-of-pattern-space pattern. The pattern $ matches the null string at the end of the pattern space. With this pattern you can avoid using rev as advised above.

      $ echo machine1a | sed 's/a$/b/'
  machine1b
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  2. % echo machine1a | rev | sed s'/a/b/' | rev
machine1b

    I can't find a way to do this with sed alone. There is a flag to the s operation specifies to only replace the Nth match, but counting from the end doesn't work.

    % echo machine1a | sed s'/a/b/2'
machine1b
    • 2

  3. this is not possible using one simple sed expression. Instead do something like this ie. use bash's string manipulation capabilities:

    var=machine1a; echo "${var%?}b"

    But if you REALLY need sed then you can run the following command:

    echo machine1a | sed s'/\(.*\)\(.\)$/\1b/g'

    Sorry for confusion above by saying that it was not possible. I normally do this kind of stuff in bash using bash's string handling capabilities.

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