Tr (Unix)

tr (abbreviated from translate or transliterate) is a command in Unix-like operating systems. When executed, the program reads from the standard input and writes to the standard output. It takes as parameters two sets of characters, and replaces occurrences of the characters in the first set with the corresponding elements from the other set.

Examples

Translate "\n" to "\r\n":

$ tr -A "\12" "\15\12" < input1  > output1
$ tr -A "^M" "\15\12"  < output1 > output2

The following inputs shift the input letters of the alphabet back by one character.

$ echo "ibm 9000" >computer.txt
$ tr a-z za-y <computer.txt
hal 9000

In some older versions of tr (not POSIX-compliant), the character ranges must be enclosed in brackets, which must then be quoted against interpretation by the shell:

$ tr "[a-z]" "z[a-y]" <computer.txt

If it's not known in advance which variant of tr is being invoked, then in this example one would have to write the ranges in unabbreviated form (tr abcdefghijklmnopqrstuvwxyz zabcdefghijklmnopqrstuvwxy). For some applications, a single invocation is portable despite containing ranges: ROT13 can be portably implemented as tr "[A-M][N-Z][a-m][n-z]" "[N-Z][A-M][n-z][a-m]". (This works because the brackets, which are not part of the range syntax in POSIX tr, align properly in the two strings, and hence will be safely interpreted as a request to map the bracket character to itself.) Ruby and Perl also have an internal tr operator, which operates analogously.

See also

• Sed
• List of Unix programs

External links

• The tr Command - by The Linux Information Project (LINFO)
• [1] The program's manpage