LINUX COMMANDS

tr [options] [string1 [string2]]

Translate characters. Copy standard input to standard output, substituting characters from string1 to string2, or deleting characters
in string1.

Options
-c, -C, --complement
Complement characters in string1 with respect to ASCII 001-377.
-d, --delete
Delete characters in string1 from output.
-s, --squeeze-repeats
Squeeze out repeated output characters in string2.
-t, --truncate-set1
Truncate string1 to the length of string2 before translating.
--help
Print help message and then exit.
--version
Print the version number and then exit.

Special characters
Include brackets ([ ]) where shown.
\a Ctrl-G (bell)
\b Ctrl-H (backspace)
\f Ctrl-L (form feed)
\n Ctrl-J (newline)
\r Ctrl-M (carriage return)
\t Ctrl-I (tab)
\v Ctrl-K (vertical tab)
\nnn
Character with octal value nnn
\\ Literal backslash
char1-char2
All characters in the range char1 through char2. If char1 does
not sort before char2, produce an error.
[char*]
In string2, expand char to the length of string1.
[char*number]
Expand char to number occurrences. [x*4] expands to xxxx,
for instance.
[:class:]
Expand to all characters in class, where class can be:
  alnum
Letters and digits
  alpha
Letters

blank
Whitespace
cntrl
Control characters
digit
Digits
graph
Printable characters except space
lower
Lowercase letters
print
Printable characters
punct
Punctuation
space
Whitespace (horizontal or vertical)
upper
Uppercase letters
xdigit
Hexadecimal digits
[=char=]
The class of characters to which char belongs.

Examples:

cat file | tr 'A-Z' 'a-z'                         Change uppercase to lowercase in a file

tr ' ' '\012' < file                              Turn spaces into newlines (ASCII code 012):

cat file | tr -s "" "\012" > new.file       Strip blank lines from file and save in new.file:

echo 'Test' | tr '[:lower:]' '[:upper:]'    Case conversion

tr '\0' '\n' < /proc/$$/environ             Display the startup environment for any process