Linux tr command - replace, abbreviate and/or delete characters from standard input

Linux tr command: replace, abbreviate and/or delete characters from standard input

Linux tr command Function Description

Use the tr command to replace, reduce and/or delete characters from standard input and write the result to standard output. Replacement is performed only when both string 1 and string 2 are specified and there is no -d option.

The tr command can replace, compress, and delete characters from standard input. It can turn one set of characters into another, and is often used to write beautiful one-line commands that are very powerful.

Linux tr command Syntax

tr [Option] [String 1] [String 2]

The meaning of each option in the command is shown in the following table.

Option	Description
-c or –complerment	First complete the string 1
-d or –delete	Delete the content of match string 1, and do not replace it
-s or –squeeze-repeats	If there are consecutive repetitions of characters matching string 1 in the input sequence, they are uniformly reduced to the length of one character when replaced
-t or –truncate-set1	First truncate the length of string 1 to be equal to that of string 2

Strings can generally be understood literally. The parsing sequence shown in the following table can be used in the tr command.

• String 1: Specifies the original character set to be converted or deleted. When performing the conversion operation, you must use the parameter String 2 to specify the target character set for conversion. However, when performing a delete operation, the parameter String 2 is not required.
• String 2: Specifies the target character set to be converted.

Parsing Sequence	Description
\NNN	Octal value of NNN characters (1 to 3 digits)
\\	Backslash
\a	Terminal chirp
\b	Backspace
\f	Change page
\n	A newline
\r	enter
\t	Horizontal TAB characters
\v	Vertical TAB characters
Character 1- Character 2	All characters experienced in ascending order from Character 1 to Character 2
character *	For Character 2, the specified characters will be copied continuously until they match the length of Character 1.
Characters * times	The character is copied a specified number of times, and if the number starts with 0, it is considered as an octal number.
[:alnum:]	All letters and numbers
[:alpha:]	All letters
[:blank:]	All horizontally aligned blank characters
[:cntrl:]	All control characters
[:digit:]	All numbers
[:graph:]	All printable characters, excluding spaces
[:lower:]	All lowercase letters
[:print:]	All printable characters, including spaces
[:punct:]	All punctuation characters
[:space:]	All blank characters in horizontal or vertical alignment
[:upper:]	All capital letters
[:xdigit:]	All hexadecimal numbers
[=characters=]	All characters equal to the specified character

Linux tr command Example

Display the /root/apidemos.com.txt file and replace lowercase letters with uppercase letters in the output

Display the contents of the /root/a file, replacing the character a with d in the output

[root@rhel ～]# cat /root/a|tr a d
d
A
b
B

Converts input characters from uppercase to lowercase

echo "HELLO WORLD" | tr 'A-Z' 'a-z'
hello world

‘A-Z’ and ‘a-z’ are sets, and sets can be formulated by themselves, for example: ‘ABD-}’, ‘bB.,’, ‘a-de-h’, ‘a-c0-9’ are all sets, and ‘\n’, ‘\t’ can be used in sets, and other ASCII characters can be used.

Use tr to delete characters

echo "hello 123 world 456" | tr -d '0-9'
hello  world 

Converting tabs to spaces

cat text | tr '\t' ' '

Character set complement, remove all characters from the input text that are not in the complement

echo aa.,a 1 b#$bb 2 c*/cc 3 ddd 4 | tr -d -c '0-9 \n'
 1  2  3  4

In this example, the complement set contains the numbers 0~9, spaces and the line break \n, so they are not deleted, and all other characters are deleted.

Compress characters with tr to compress repetitive characters in the input

echo "thissss is      a text linnnnnnne." | tr -s ' sn'
this is a text line.

Clever use of tr for number summation

echo 1 2 3 4 5 6 7 8 9 | xargs -n1 | echo [(tr '\n' '+') 0 ]

Remove the ‘^M’ character from the Windows file "caused by"

cat file | tr -s "\r" "\n" > new_file
or
cat file | tr -d "\r" > new_file

The character classes that tr can use

[:alnum:]: letters and numbers
[:alpha:]: letters
[:cntrl:]: control (non-printing) characters
[:digit:]: numbers
[:graph:]: graph characters
[:lower:]: lowercase letters
[:print:]: printable characters
[:punct:]: punctuation characters
[:space:]: blank characters
[:upper:]: uppercase letters
[:xdigit:]: hexadecimal characters  

Usage:

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