Original author(s) |
Douglas McIlroy ( AT&T Bell Laboratories) |
---|---|
Developer(s) | Various open-source and commercial developers |
Initial release | November 1973 |
Repository | |
Written in | C |
Operating system | Unix, Unix-like, Plan 9, Inferno, OS-9, MSX-DOS, IBM i |
Platform | Cross-platform |
Type | Command |
License |
coreutils:
GPLv3+ Plan 9: MIT License |
tr is a command in Unix, Plan 9, Inferno, and Unix-like operating systems. It is an abbreviation of translate or transliterate, indicating its operation of replacing or removing specific characters in its input data set.
The utility reads a byte stream from its standard input and writes the result to the standard output. As arguments, it takes two sets of characters (generally of the same length), and replaces occurrences of the characters in the first set with the corresponding elements from the second set. For example,
tr 'abcd' 'jkmn'
maps all characters a to j, b to k, c to m, and d to n.
The character set may be abbreviated by using character ranges. The previous example could be written:
tr 'a-d' 'jkmn'
In
POSIX-compliant versions of tr
, the set represented by a character range depends on the
locale's
collating order, so it is safer to avoid character ranges in scripts that might be executed in a locale different from that in which they were written. Ranges can often be replaced with
POSIX character sets such as [:alpha:].
The s
flag causes tr
to compress sequences of identical adjacent characters in its output to a single token. For example,
tr -s '\n'
replaces sequences of one or more newline characters with a single newline.
The d
flag causes tr
to delete all tokens of the specified set of characters from its input. In this case, only a single character set argument is used. The following command removes carriage return characters.
tr -d '\r'
The c
flag indicates the complement of the first set of characters. The invocation
tr -cd '[:alnum:]'
therefore removes all non-alphanumeric characters.
The original version of tr
was written by
Douglas McIlroy and was introduced in
Version 4 Unix.
[1]
The version of tr
bundled in
GNU
coreutils was written by Jim Meyering.
[2] The command is available as a separate package for
Microsoft Windows as part of the
UnxUtils collection of
native
Win32
ports of common GNU Unix-like utilities.
[3] It is also available in the
OS-9 shell.
[4] A tr
command is also part of
ASCII's MSX-DOS2 Tools for
MSX-DOS version 2.
[5] The tr command has also been ported to the
IBM i operating system.
[6]
Most versions of tr
, including GNU tr
and classic Unix tr
, operate on single-byte characters and are not
Unicode compliant. An exception is the
Heirloom Toolchest implementation, which provides basic Unicode support.
Ruby and Perl also have an internal tr operator, which operates analogously. [7] [8] Tcl's string map command is more general in that it maps strings to strings while tr maps characters to characters. [9]