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 "$message"  |  sed -e 's/^[[:lower:]]/\u&/' -e 's/\([^\]\)\([[:lower:]]\)/\1\u\2/g' \
                                                 -e 's/\([^\]\)\([[:lower:]]\)/\1\u\2/g'

• -e 's/^[[:lower:]]/\u&/'  If the first character in the string (or, more generally, the first character on a line) is a lower-case letter, capitalize it.  Because the first character on a line can’t be escaped.  Duh.  That’s a no-brainer.

• -e 's/\([^\]\)\([[:lower:]]\)/\1\u\2/g'  Look at the line two characters at a time.  If a lower-case letter is preceded by something other than a backslash, leave the preceding character alone, and capitalize the lower-case letter.

  You might think that this would be enough to process the entire line.  Unfortunately, since it processes the line two characters at a time, it gets only every other letter:

  $ echo "first line\nsecond line" | sed -e 's/\([^\]\)\([[:lower:]]\)/\1\u\2/g'
  fIrSt LiNe\nSeCoNd LiNe
  

  so,

• -e 's/\([^\]\)\([[:lower:]]\)/\1\u\2/g'  Do the exact same thing a second time.  This will pick up the letters that were skipped on the first pass.

---

Alternative version:

echo "$message" | sed -e 's/^[[:lower:]]/\u&/' \
                                  -e ': loop; s/\([^\]\)\([[:lower:]]\)/\1\u\2/g; t loop'

Basically the same as the first version, but, instead of repeating the second s command, it iterates it with a loop.

---

Unfortunately, this will not work correctly for double backslashes:  foo\\bar will become FOO\\bAR, even though the b should be capitalized, since the \\ is an escaped backslash, and so should not cause the b to be escaped.

Answer 4

I'd consider evaluating the \n and other escape sequences at the point that the variable was defined. Here $message actually contains a newline.

message=$(printf '%b' 'First Line\nSecond Line')
echo "${message^^}"

Output

FIRST LINE
SECOND LINE

Answer 5

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

Answer 6

Using Raku (formerly known as Perl_6)

~$ echo 'a\nb'
a\nb
~$ echo 'a\nb' | raku -pe 's:g/ <!after "\\"> (.) /{$0.uc}/;'
A\nB
~$ echo "a\\nb"
a\nb
~$ echo "a\\nb" | raku -pe 's:g/ <!after "\\"> (.) /{$0.uc}/;'
A\nB

Above uses a negative look-behind assertion, <!after "\\">, to select out all characters except those immediately after a \ backslash. Selected characters are then uppercased with Raku's .uc routine.

Certainly it's safer to provide the regex with a custom <-[ … ]> negative character class, sparing backslashed characters like \n and \t from being uppercased. (FYI, custom positive character classes are written <+[ … ]> or more simply <[ … ]> in Raku).

Below, using Raku's "Q-lang" (quoting language) to feed the substitution operator a string. In all four examples below \n is returned (not uppercase \N). Note in the third example how \n is operationally-interpreted as a newline character, and this remains unchanged in the fourth example, telling us that \n still exists in that string (i.e. it has NOT been uppercased to \N):

~$ raku -e 'put Q<a\nb>'
a\nb
~$ raku -e 'put Q<a\nb>' | raku -pe 's:g/ <!after "\\"> (<-[nt]>) /{$0.uc}/;'
A\nB
~$ raku -e 'put Q:b<a\nb>'
a
b
~$ raku -e 'put Q:b<a\nb>' | raku -pe 's:g/ <!after "\\"> (<-[nt]>) /{$0.uc}/;'
A
B

NOTE, see: "Place an escape sign before every non-alphanumeric characters" for Raku answers to a related question on StackOverflow.

References:
https://docs.raku.org/language/quoting
https://docs.raku.org/language/regexes#Literals_and_metacharacters
https://raku.org