CODEWITHSUNDEEP
bashtr
Jan Vorcak
Jan Vorcak

Reputation: 20019

tr '[z-a]' '[a-z]' yields error message

I want to emulate rev command (on alphabet) with the tr command

So I did this

echo abcdefghijklmnopqrstuvxyz | tr '[z-a]' '[a-z]'

That gives me

tr: range-endpoints of `z-a' are in reverse collating sequence order

So I tried 

echo abcdefghijklmnopqrstuvxyz | tr 'abcdefghijklmnopqrstuvxyz' 'zyxvutsrqponmlkjihgfedcba'

and it works ok, output is zyxvutsrqponmlkjihgfedcba

That is wrong with tr '[z-a]' '[a-z]'?

If I specify tr '[a-c]' '[c-a]' it also works fine.

Any help would be appreciated

Thank you

Upvotes: 4

Views: 2881

Answers (1)

shellter
shellter

Reputation: 37298

I think your lucky with the '[c-a]' thing, My tr says tr: [c-a]: invalid destination string, which is what I would expect.

Character ranges, i.e. [a-z], in all the languages I've dealt with, need to ascend in value. Be happy that you've already figured out your solution.

Or write a function that you can use like tr "[a-z]" "[$( revCharRange a-z )]" (which would be more expensive due to the sub-shells required to create the reverse character range.

Edit where revCharRange a-z would output zyxw...cba

I hope this helps.

Upvotes: 4

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