8

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
5

In bash you could do:

$ str="abcdefgh"
$ foo=${str:2};echo ${str:0:2}${foo^}
abCdefgh

In Perl:

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

Or

$ perl -ple 's/(..)(.)/$1.uc($2)/e; ' <<<$str
abCdefgh
  • 1
    What is purpose of ~ in perl solution? – cuonglm Nov 16 '14 at 5:15
  • @cuonglm a typo. It was left over from a previous versin I tried where I was using $ARGV[0]=~ instead of <<<$str. Thanks. – terdon Nov 16 '14 at 12:16
  • 2
    The bash can be shortened with foo=${str:2} and ${foo^}, which only capitalizes the first character in the string. – chepner Nov 16 '14 at 15:51
7

With GNU sed (possibly others)

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

With awk

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

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.

  • That's really cool, I didn't know that xor-ing an ascii character with space inverts its case. – ryanmjacobs Nov 16 '14 at 7:08

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