Convert all text from uppercase to lowercase and vice versa?

Question

My question is how can I convert all text from uppercase to lowercase and vice versa? That is to change the cases of all the letters. It has to be done with a sed replacement somehow.

Answer 1

Here is a straight way in sed:

$ echo qWeRtY | sed -e 'y/abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ/ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz/'
QwErTy

or a shorter way with GNU sed, working with any character for which a lowercase<->uppercase conversion exists in your locale:

$ echo qWeRtY | sed -E 's/([[:lower:]])|([[:upper:]])/\U\1\L\2/g'
QwErTy

if you can use another tools, like:

perl (limited to ASCII letters):

$ echo qWeRtY | perl -pe 'y/[a-z][A-Z]/[A-Z][a-z]/'
QwErTy

perl (more generally):

$ echo 'αΒγ' | perl -Mopen=locale -pe 's/(\p{Ll})|(\p{Lu})/uc($1).lc($2)/ge'
ΑβΓ

Answer 2

POSIXly, that can't be done with sed except by providing the complete set of letters you want to transliterate as @cuonglm has shown.

It could be done with tr though, and that's what tr is for (transliterate):

tr '[:lower:][:upper:]' '[:upper:][:lower:]'

However, on Linux, it's got limitations. Of the 3 tr implementations commonly found on Linux-based systems:

• with GNU tr, that only works for single-byte character sets. For instance, on Stéphane Chazelas in UTF-8 locales, that gives sTéPHANE cHAZELAS instead of sTÉPHANE cHAZELAS. That's a known limitation of GNU tr.
• with tr from the heirloom toolchest, that doesn't work (you get stéphane chazelas).
• That's not the kind of thing busybox tr will do.

On FreeBSD that works OK though. You'd expect it to work OK in certified Unix systems as well.

---

The bash shell has a dedicated operator for that:

in=AbCdE
out=${in~~}

With zsh -o extendedglob:

out=${in//(#b)(([[:lower:]])|([[:upper:]]))/${(U)match[2]}${(L)match[3]}}

Answer 3

If your main objective is to convert a file from lowerclass to upperclass, why dont you use tr and STDOUT to convert your file:

$cat FILENAME | tr a-z A-Z > FILENAME2

Where FILENAME is your original file. Where FILENAME2 is your converted output file.

Answer 4

Though this has the same limitations already mentioned as the tr solution offered by Stéphane Chazelas, it is another way to do it:

{   echo QWERTYqwerty | dd conv=lcase
    echo QWERTYqwerty | dd conv=ucase 
} 2>/dev/null

OUTPUT

qwertyqwerty
QWERTYQWERTY

I dump stderr into /dev/null there because dd also provides statistics of all its operations on the 2 file descriptor. This can be useful depending on what you're doing, but wasn't for this demonstration. All of the other stuff you can do with dd still applies, for instance:

echo QWERTYqwerty | dd bs=1 cbs=6 conv=unblock,ucase 2>/dev/null

OUTPUT:

QWERTY
QWERTY

Answer 5

using awk:

awk '{print tolower($0)}' file.txt | tee file.txt

Answer 6

ruby has a string method for that, similar usage from command line like perl

$ echo 'qWeRtY' | ruby -pe '$_.swapcase!'
QwErTy

See also ruby-doc Encoding

$ ruby -e 'puts Encoding.default_external'
UTF-8
$ echo 'αΒγ'  | ruby -pe '$_.swapcase!'
ΑβΓ

Answer 7

Keep simple thing simple. The filter designed to translate characters is tr.

echo 1ude1UDE | tr [:upper:][:lower:] [:lower:][:upper:]