read a variable character by character, substitute characters with something else

vipervenom25 · #1 (**permalink**) 06-06-2008

im having trouble doing this:

i have a variable with 2 characters repeating e.g. aababbbaaaababaabbaabbba

is there a way i can search the variable for a's and b's and then change a's to b's and b's to a's?

im guessing its like getting the 1's compliment of the string

im doing this in BASH, and ive looked into seeing if sed or awk could help but i got nothing

any help would be greatly appreciated
thanks

fabtagon · #2 (**permalink**) 06-06-2008

echo $var | tr a z | tr b a | tr z b

more info: man tr
we use z as temporary placeholder as we can only transform one character a time

joeyg · #3 (**permalink**) 06-06-2008

In order to switch things, the first cannot immediately be switched to the second. Take a look at the following where I ...
translate a to z
translate b to a
translate z to b

Code:

> echo $var1
aababbbaaaababaabbaabbba
> var2=$(echo $var1 | tr a z)
> var3=$(echo $var2 | tr b a)
> var4=$(echo $var3 | tr z b)
> echo $var4
bbabaaabbbbababbaabbaaab

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