Skip to content
Pit

tr command in UNIX

Terminal window
tr [OPTION]... SET1 [SET2]

Introduction

Section titled “Introduction”

Translate, squeeze, and/or delete characters from standard input, writing to standard output.

Options

Section titled “Options”

The most useful options are:

  • -c, -C, --complement: use the complement of SET1
  • -d, --delete: delete characters in SET1 (do not translate)
  • -s, --squeeze-repeats: replace each sequence of a repeated character that is listed in the last specified SET, with a single occurrence of that character
  • -t, --truncate-set1: first truncate SET1 to length of SET2

SETs are strings of characters. The most useful interpreted sequences are:

  • \NNN: character with octal value NNN (1 to 3 octal digits)
  • \\: backslash
  • \b: backspace
  • \n: new line
  • \t: horizontal tab
  • \v: vertical tab
  • CHAR1-CHAR2: all characters from CHAR1 to CHAR2 in ascending order
  • [CHAR*]: in SET2, copies of CHAR until length of SET1
  • [:alnum:]: all letters and digits
  • [:alpha:]: all letters
  • [:blank:]: all horizontal whitespace
  • [:digit:]: all digits
  • [:graph:]: all printable characters, not including space
  • [:lower:]: all lower case letters
  • [:punct:]: all punctuation characters
  • [:upper:]: all upper case letters
  • [:xdigit:]: all hexadecimal digits
  • [=CHAR=]: all characters which are equivalent to CHAR.

Please refer to the manual to see all the sequences.

However, translation occurs if -d is not given and both SET1 and SET2 appear.

The option -t may be used only when translating. SET2 is extended to length of SET1 by repeating its last character as necessary. Excess characters of SET2 are ignored.

Option -s uses the last specified SET, and occurs after translation or deletion.

Examples

Section titled “Examples”

Here are some examples:

Terminal window
my_string="rock,paper,scissor"
echo $my_string
rock,paper,scissor


echo $my_string | tr ',' ' '
rock paper scissor


# enclose comma sign between single quotes is not mandatory
# echo $my_string | tr , '\n'
echo $my_string | tr ',' '\n'
rock
paper
scissor


echo $my_string | tr -d ,
rockpaperscissor


# transform ',' into '\n' and 'r' into 'X'
echo $my_string | tr ',r' '\nX'
Xock
papeX
scissoX


# transform lowercase letters to uppercase
echo $my_string | tr [:lower:] [:upper:]
ROCK,PAPER,SCISSOR


# transform lowercase letters to uppercase and spaces to dashes
echo " William Shakespeare" | tr '[:upper:] ' '[:lower:]-'
-william-shakespeare


# override the variable
my_string="I am 20 years old"
# transform digits to 'N'
echo $my_string | tr [:digit:] 'N'
I am NN years old


# transform all punctuation characters to '\'
my_string="Hi! How are you? I'm 20 years old."
echo $my_string | tr [:punct:] '\\'
Hi\ How are you\ I\m 20 years old\


# HEX values are the digits from 0 to 9 and letters from 'A' (or 'a') to 'F' (or 'f')
my_string="The color is: A3"
# transform all hexadecimal characters to '@'
echo $my_string | tr [:xdigit:] '@'
Th@ @olor is: @@

tr command works as well with files.

Lets’ download silvia.txt poem by William Shakespeare and put it in your /Desktop directory.

Terminal window
cd Desktop/
# redirect standard input to 'silvia.txt' file
tr [:lower:] [:upper:] < silvia.txt
WHO IS SILVIA? WHAT IS SHE?
THAT ALL OUR SWAINS COMMEND HER?
HOLY, FAIR, AND WISE IS SHE;
# ... (the rest of the file)


# redirect standard input to 'silvia.txt' file
# and redirect standard output to 'uppercase-silvia.txt'
tr [:lower:] [:upper:] < silvia.txt > uppercase-silvia.txt
cat uppercase-silvia.txt
WHO IS SILVIA? WHAT IS SHE?
# ...

Quotes

Section titled “Quotes”

Manual reference: