Removing words comprised of upper and lowercase letters?

Question

I have file called file.txt. In this file there are words composed of upper and lowercase letters, also there are words consist of upper or lowercase letters and numbers. I would like to filter this file, so the output is free of the words that contain both upper and lower case letters. For example, the input file.txt:

Aaa
aBb
aB
Aa12
12aA
123
123Ab
AAA
aaa

In this file there are words with upper and lowercase letters (e.g. Aaa, aBp), and words contain upper/lower case letters AND digits (e.g. 123Ab). In addition, to words contain only small letters (e.g. aaa), or only capital letters (e.g. AAA). I would like to remove only the words that contain upper AND lowercase letters (e.g. Aaa, aBp), so the output is as follows:

Aa12
12aA
123
123Ab
AAA
aaa

Any ideas?

Answer 1

grep -Exv '[A-Za-z]*([A-Z][a-z]|[a-z][A-Z])[A-Za-z]*'

Explanation

• The idea is to match the opposite of what you want first, i.e. those lines that contain only upper- and lower-case letters. This uses grep -Ex, i.e. grep with extended regex, match the whole line. The -v flag then negates the regex, i.e. return those lines that do not match the following regex.
• The central part ([A-Z][a-z]|[a-z][A-Z]) matches a single upper-case letter followed by a lower-case letter, or vice versa.
• The outer part [A-Za-z]*...[A-Za-z]* means that the rest of the line must comprise upper- or lower-case letters only.

Answer 2

With grep and assuming one word per line:

grep -E '[[:digit:]]|^([[:lower:]]+|[[:upper:]]+)$'

To report all the matching words in a text, with potentially several words per lines, words delimited by non-word characters:

<text tr -cs '[:alnum:][:digit:]_' '[\n*]' |
  grep -E '[[:digit:]]|^([[:lower:]]+|[[:upper:]]+)$'

Note that you need a POSIX compliant tr implementation, GNU tr won't do. On GNU systems, you can use sed instead:

<text sed -E 's/\W+/\n/g' |
  grep -E '[[:digit:]]|^([[:lower:]]+|[[:upper:]]+)$'

Answer 3

To restate your requirements, you want to keep a word if:

• it contains a digit non-letter, or
• it is all uppercase letters, or
• it is all lowercase letters

Then

awk '/[^[:alpha:]]/ || /^[[:upper:]]+$/ || /^[[:lower:]]+$/' file

Answer 4

Using sed:

$ sed -E -e '/[0-9]/b' -e '/^[A-Z]+$/b' -e '/^[a-z]+$/b' -e 'd' <file
Aa12
12aA
123
123Ab
AAA
aaa

Annotated sed script:

/[0-9]/b        # Digits are present, branch to end
/^[A-Z]+$/b     # Only uppercase characters present, branch to end
/^[a-z]+$/b     # Only lowercase characters present, branch to end
d               # Delete line, start next cycle
                # (at end, implicit print)

Alternatively,

sed -E -e '/[[:digit:]]/b' -e '/^[[:upper:]]+$/b' -e '/^[[:lower:]]+$/b' -e 'd' <file

There may be a difference between this and the first sed script depending on your locale.