Change case of n-th letter in a string

Question

I want to change the case of the n-th letter of a string in BASH (or any other *nix tools, e.g. sed, awk, tr, etc).

I know that you can change the case a whole string using:

${str,,} # to lowercase
${str^^} # to uppercase

Is it possible to change the case of the 3rd letter of "Test" to uppercase?

$ export str="Test"
$ echo ${str^^:3}
TeSt

Solution 1

In bash you could do:

$ str="abcdefgh"
$ foo=${str:2}  # from the 3rd letter to the end
echo ${str:0:2}${foo^} # take the first three letters from str and capitalize the first letter in foo.
abCdefgh

In Perl:

$ perl -ple 's/(?<=..)(.)/uc($1)/e; ' <<<$str
abCdefgh

Or

$ perl -ple 's/(..)(.)/$1.uc($2)/e; ' <<<$str
abCdefgh

Solution 2

With GNU sed (possibly others)

sed 's/./\U&/3' <<< "$str"

With awk

awk -vFS= -vOFS= '{$3=toupper($3)}1' <<< "$str"

Solution 3

Another perl:

$ str="abcdefgh"
$ perl -pe 'substr($_,2,1) ^= " "' <<<"$str"
abCdefgh

• The general form is substr($_,n,1) where n is the position of letter you want to invert the case (0-based index).

• When you xor an ASCII character with space, you invert its case.

Comments

[cuonglm]

What is purpose of ~ in perl solution?

[terdon]

@cuonglm a typo. It was left over from a previous versin I tried where I was using $ARGV[0]=~ instead of <<<$str. Thanks.

[chepner]

The bash can be shortened with foo=${str:2} and ${foo^}, which only capitalizes the first character in the string.