Convert all small words (2-3 characters) to upper case with awk or sed

Question

I need all 2-3 character words completely capitalized. 1 character and 4+ character words need to be remain untouched.

Input:

cat Example
Dog
I
Fish
su
Su adm
Amd Cat ignore

Expected output:

CAT Example
DOG
a
Fish
SU
SU ADM
ADM CAT ignore

Answer 1

Using GNU sed

$ sed -E 's/\<[[:alpha:]]{2,3}\>/\U&/g' input_file
DOG
I
Fish
SU
SU ADM
AMD CAT ignore

Answer 2

I would use perl instead:

$ perl -pe 's/\b\w{2,3}\b/uc($&)/eg' file
CAT Example
DOG
I
Fish
SU
SU ADM
AMD CAT ignore

If your file contains non-ASCII characters encoded in UTF-8 and your locale uses UTF-8 as the charmap, for example the string sté that should become STÉ, then use:

$ perl -C -pe 's/\b\w{2,3}\b/uc($&)/eg' file
CAT Example
DOG
I
Fish
SU
SU ADM
AMD CAT ignore
STÉ

Answer 3

This is a solution with awk:

awk '{ for (i=1; i<=NF; i++) { if (length($i) <= 3) { $i=toupper($i) } } }1' infile

Answer 4

Using Raku (formerly known as Perl_6)

raku -pe 's:g/<?wb> \w**2..3 <?wb>/{$/.uc}/;'  

OR

raku -pe 's:g/<|w> \w**2..3 <|w>/{$/.uc}/;'  

OR

raku -pe 's:g/<< \w**2..3 >>/{$/.uc}/;' 

The Raku code above is a fairly direct translation of @terdon's Perl code. Word boundaries are written either <?wb> or <|w> in Raku. These can be negated as <!wb> or <!|w>, respectively. In the last example, a left word-boundary is << and a right word boundary is >>. Raku's match variable is $/, which can also be spelled $<>.

You can change the target class from \w to <alpha> or <alnum> or even to <:Letter> (abbreviated <:L>). Nota bene: \w and <alpha> and <alnum> will match underscore while <:Letter> and <:L> will not.

All the classes mentioned immediately above are Unicode-aware so any sort of "case-folding" shouldn't be a problem. You can write regexes targeting Unicode-defined <:Ll> lowercase letters and/or Unicode-defined <:Lu> uppercase letters, and you can even compare letters with the .fc "foldcase" routine.

Sample Input:

cat Example
Dog
I
Fish
su
Su adm
Amd Cat ignore
sté
a
Xa
Xá
Xå
Xà
Xä
Xb
Xß
Xœ
Xþ

Sample Output:

CAT Example
DOG
I
Fish
SU
SU ADM
AMD CAT ignore
STÉ
a
XA
XÁ
XÅ
XÀ
XÄ
XB
XSS
XŒ
XÞ

https://docs.raku.org/language/regexes#Anchors
https://raku.org