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Match Character Classes

Vowels​

echo abcdefghijk | grep -e "[aeiou]"
# will find a,e,i

Range​

echo abcdefghijkAC04 | grep -e "[a-zA-D0-9]"

Negation character ^ - don't match​

echo abcdefghijkAC04 | grep -e "[^a-zA-D0-9]"
# AC04

select with or (alternation)​

echo "cat dog" | grep -e "[cat|fish]" # selects cat

Using metacharacters​

select only characters (including _)​

echo "P45SW0%$#_#2#4RD" | grep -e "\w" # selects P45SW0RD

select only special characters​

echo "P45SW0%$#_#2#4RD" | grep -e "\W" # selects %$#_##

select all digits (-P flag enables perl regex)​

echo "P45SW0%$#_#2#4RD" | grep -P "\d" 
# matches

select all except digits (-P flag enables perl regex)​

echo "P45SW0%$#_#2#4RD" | grep -P "\D" # matches

select tabs, newlines​

echo "some text with tab" | grep -P "\t" 
# matches tab  

echo "some text with tab" | grep -P "\n" 
# matches newline

echo "some text with tab" | grep -P "\s" 
# matches spaces

echo "some text with tab" | grep -P "\S" 
# matches sometextwiththab

# match square brackets
echo "[]" | grep -e "\[\]"