Tr is used to convert characters from standard input through replacement or deletion. Tr is mainly used to delete control characters in a file or convert characters.
Note: tr can only replace, contract, and delete characters, but cannot replace strings.
Tr command format:
Tr-c-d-s ["string1_to_translate_from"] ["string2_to_translate_to"] file
Here:
-C: replace this character set with the supplement set of Character Set 1. the character set must be ASCII.
-D: delete all input characters in string 1.
-S: deletes all recurring character sequences. Only the first string is retained. The duplicate string is compressed into one string.
File: conversion file name. Although other formats can be used for input, this format is the most commonly used.
Character range:
When specifying the content of string 1 or string 2, you can only use a single character or string range or list.
A string consisting of characters in a-z.
[A-Z] A string consisting of characters within the A-Z.
[0-9] numeric string.
\ Octal is a three-digit octal number, which corresponds to valid ASCII characters.
[O * n] indicates the repeated occurrence of the character O for a specified number of times. Therefore, [O * 2] matches the OO string.
Different expressions of specific control characters in tr
Shorthand meaning octal
\ A Ctrl-G ringtone \ 007
\ B Ctrl-H return character \ 010
\ F Ctrl-L line feed \ 014
\ N Ctrl-J New Line \ 012
\ R Ctrl-M press enter \ 015
\ T Ctrl-I tab key \ 011
\ V Ctrl-X \ 030
Example
(1 remove repeated lower-case characters in oops.txt (#-s retains the first character)
[Root @ localhost ~] # Cat oops.txt
Ddddfffabccccc
Lerrrrdddd
[Root @ localhost ~] # Tr-s "[a-z]" <oops.txt> result.txt
[Root @ localhost ~] # Cat result.txt
Dfabc
Lerd
(2) Delete empty rows
[Root @ localhost ~] # Cat oops.txt
Ddddfffabccccc
Lerrrrdddd
[Root @ localhost ~] # Tr-s "[\ 012]" <oops.txt> result.txt
[Root @ localhost ~] # Cat result.txt
Ddddfffabccccc
Lerrrrdddd
(3) Delete all empty rows
[Root @ localhost ~] # Cat oops.txt
Ddddfffabccccc
Lerrrrdddd
[Root @ localhost ~] # Tr-d "[\ 012]" <oops.txt> result.txt
[Root @ localhost ~] # Cat result.txt
Ddddfffabccccclerrrrdddd
(4) small to uppercase
[Root @ localhost ~] # Cat oops.txt
Ddddfffabccccc
Errrrdddd
[Root @ localhost ~] # Cat oops.txt | tr "[a-z]" "[A-Z]"> result.txt
[Root @ localhost ~] # Cat result.txt
DDDDFFFABCCCCC
ERRRRDDDD
(5) Delete the specified characters (#-d is different from-s,-d is deleted, but-s retains the first character)
[Root @ localhost ~] # Cat oops.txt
Ddddfffabccccc
Errrrdddd
[Root @ localhost ~] # Cat oops.txt | tr-d "[bd]"> result.txt
[Root @ localhost ~] # Cat result.txt
Fffaccccc
Errrr
[Root @ localhost ~] # Cat oops.txt | tr-s "[bd]"> result.txt
[Root @ localhost ~] # Cat result.txt
Dfffabccccc
Errrrd
(6) Replace the specified character (# One-to-one replacement)
[Root @ localhost ~] # Cat oops.txt
Ddddfffabccccc
Errrrdddd
[Root @ localhost ~] # Cat oops.txt | tr "[bd]" "[BD]"> result.txt
[Root @ localhost ~] # Cat result.txt
DDDDfffaBccccc
ErrrrDDDD
