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The tr command is useful for translating characters from one set to another. The syntax of the command is tr SET1 [SET2].

For example, the following will capitalize the output of the date command:

[student@localhost dictionary]$ date
Sat Dec 3 20:15:05 PST 2016
[student@localhost dictionary]$ date | tr 'a-z' 'A-Z'
SAT DEC 3 20:15:18 PST 2016

Note that in order to use the tr command on a file, you must redirect the file into the tr command, like so, because the tr command does not accept files as arguments:

tr 'a-z' 'A-Z' < file

Important options include the following:

Option Description
-d Used when the second set is omitted; it deletes the matching characters. For example, the following deletes all numbers from the output of the date command: date | tr -d '0-9'.
-s Repeated matching characters are converted into a single character before being translated. Thus, “aaabc” would be converted into “abc” and then translated to “Abc” if the command tr -s 'a' 'A' were executed.
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