Convert to uppercase, except for escaped characters

Question

The methods I found break things further down the line by also affecting linebreaks.
For example...

$ message="First Line\nSecond Line"; 
$ echo "${message^^}"
FIRST LINE\NSECOND LINE

Is there an elegant way to convert a string to uppercase, but leaving escaped characters alone, to get the following output instead?

FIRST LINE\nSECOND LINE

I could just do something convoluted like changing "\n" to 0001 or something along those lines, apply the conversion and then return 0001 to "\n". But maybe there is a better way.

Answer 1

With zsh instead of bash:

$ message="First Line\nSecond Line"
$ set -o extendedglob
$ print -r -- ${message//(#b)((\\?)|(?))/$match[2]$match[3]:u}
FIRST LINE\nSECOND LINE

In bash (or any shell) and with the GNU implementation of sed, you can do the same with:

$ printf '%s\n' "$message" | sed -E 's/(\\.)|(.)/\1\u\2/g'
FIRST LINE\nSECOND LINE

Some potentially more efficient variants as they minimise the number of substitutions:

• zsh

  print -r -- ${message//(#b)((\\?)|([^\\]##))/$match[2]$match[3]:u}
  

  or

  print -r -- ${message//(#b)((\\?)#)([^\\]##)/$match[1]$match[3]:u}
  

• their GNU sed translations:

  printf '%s\n' "$message" | sed -E 's/(\\.)|([^\\]+)/\1\U\2/g'
  

  or

  printf '%s\n' "$message" | sed -E 's/((\\.)*)([^\\]+)/\1\U\3/g'
  

Beware they convert \Mx (Meta-x, an escape sequence supported by zsh's print for instance and that expands to the 0xf8 byte ('x' + 0x80)) to \MX (0xd8). They also convert \x7a to \x7A or \u007a to \u007A or \Cx to \CX but that shouldn't be a problem as those expand to the same.

Answer 2

I'd be tempted to interpret the escape sequences into literal characters:

message="First Line\nSecond Line"
declare -u Message                       # uppercase on assignment
printf -v Message -- "${message//%/%%}"  # assign
declare -p Message                       # inspect

result

declare -u msg="FIRST LINE
SECOND LINE"

Answer 3

echo "First Line\nSecond Line"|sed -e 's/.*/\U&/g' -e 's/\\./\L&/g'

output

FIRST LINE\nSECOND LINE

Answer 4

The variable can be iterated line by line. Then concatenate the output again.

bash:

$ message="First Line\nSecond Line";
$ message=$(echo -e ${message} |while read -r line; do echo -n "${line^^}\n" ; done) && message=${message%??}
$ echo ${message} 
FIRST LINE\nSECOND LINE