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I have a file ~/foo.txt that has instances of each of the following strings

alpha-1
alpha-2
alpha-3
alpha-4
alpha-5
alpha-6
alpha-7
alpha-8
alpha-9

I would like to replace each of these alpha-X with beta-X. Simply replacing alpha- with beta- will not suffice as there are other instances of alpha- that I want to preserve.

I imagine this can be accomplished with something like

perl -p -i -e `s/alpha-SOMETHING/beta-SOMETHING/g'

but I'm not sure what SOMETHING should be. Is there a solution here?

(Of course, I could run nine one-liners but this seems very inefficient.)

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  • 1
    Replace SOMETHING like s/alpha(-[[:digit:]])\b/beta$1/g Commented Jan 15, 2016 at 22:47
  • @brian, you will have to be painfully explicit: which alphas should be replaced and which should be kept? Commented Jan 16, 2016 at 1:30
  • @Costas, perl offers the shorthand \d for [[:digit:]] Commented Jan 16, 2016 at 1:31
  • I don't see 0 in the list, so [1-9] might be appropriate here. Commented Jan 16, 2016 at 2:32
  • Note, that you're first quote is not correct. Commented May 15, 2019 at 14:05

2 Answers 2

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perl -p -i -e 's/alpha-(\d)/beta-$1/g'
  • \d matches 0...9
  • (\d) captures (saves) what was matched and assigns it to the $1 variable (if you add another capture it would be assigned to the next variable $2)
  • if the number can have more than one digit you can use \d+ to match one-or-more digits.
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1

This is the perfect use-case for a lookahead:

's/alpha(?=-\d)/beta/'

This will replace alpha with beta only if it is followed by -\d.

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