Introduction to the use of tr command

tr

translate or delete characters

I understand this to mean converting characters or deleting unwanted characters

tr [OPTION]... SET1 [SET2]

Convert characters from standard input from SET1 to SET2

Example: Convert all upper case to lower case

#echo "HELLO HOW ARE YOU? " | tr 'A-Z' 'a-z'

Note: This can only be used for stdin.

Common options:

-c: Complement set, the so-called complement set is all the characters except the given character. This option cannot be used alone.

-d: Delete specified character

-s: compresses specified duplicate characters

Examples of usage:

-d: For example, you can see that the specified collection has been deleted

#echo "Hello 1 how 2 are 3 you 4 ? " |tr -d '[0-9]' (brackets can be omitted)

-c: As you can see from the example, the specified set is all numbers, spaces, newlines, and because of the-d option, everything except the set is deleted.

#echo "Hello 1 how 2 are 3 you 4 ? " | tr -d -c '0-9 \n'

-s: As you can see from the example, the redundant spaces in the middle are compressed and only one is displayed

# echo "Hello 1 how 2 are 3 you 4 ? " | tr -s ' '

Definition set:

'A-Z' and 'a-z' are both sets, we can append characters or character classes as needed to construct sets

'Start character-end character': the way in which the meaning of a continuous set must be continuous, if not continuous, it is defined as 3 single elements, i.e. the start character,'-','end character';

Special characters: '\t' for tabs,'\n' for newlines

Character class:

alnum: all letters and numbers

digit: all numbers

alpha: all letters

space: white space character

upper: all upper case characters

lower: all lowercase characters

punct: punctuation

xdigit: hexadecimal character

How to use:

tr [: Character class:] [: Character class:]