Following is the syntax for tr. This command translates or deletes characters.
tr [OPTION] SET1 [SET2]
Following are the commonly used switches and character classes with tr.
| Command | Action |
| -d | Delete |
| -s | Squeeze repeated text in SET1 with a single occurrence in SET2 |
| [:alnum:] | Alphanumeric characters |
| [:alpha:] | All letters |
| [:digit:] | All digits |
| [:blank:] | All horizontal whitespace |
| [:space:] | All horizontal or vertical whitespace |
| [:graph:] | All printable characters, not including spaces |
| [:print:] | All printable characters, including spaces |
| [:punct:] | All punctuation characters |
| [:lower:] | All lowercase characters |
| [:upper:] | All uppercase characters |
tr is commonly used to translate or delete characters in a string. Think of tr as a simpler alternative to sed’s substitute command. Reading from stdin versus a file.
When thinking should one go with “use sed” or “use tr“, it is better to go with keeping it simple philosophy. If an operation is simple in tr; use it. However, once you start thinking about using tr recursively, it is better to use sed’s substitution command.
Typically, tr will replace [SET1] with characters in [SET2] unless the -d switch is used. Then, the characters from the stream in [SET1] will be deleted.
Using tr on our names.txt file to turn all lower case characters into an upper case −
[root@centosLocal Documents]# tr [:lower:] [:upper:] < names.txt
TED:DANIEL:101
JENNY:COLON:608
DANA:MAXWELL:602
MARIAN:LITTLE:903
BOBBIE:CHAPMAN:403
NICOLAS:SINGLETON:203
DALE:BARTON:901
AARON:DENNIS:305
SANTOS:ANDREWS:504
JACQUELINE:NEAL:102
[root@centosLocal Documents]#
Let’s turn the “:” character back into a Tab −
[root@centosLocal Documents]# tr [:] [\\t] < names.txt
Ted Daniel 101
Jenny Colon 608
Dana Maxwell 602
Marian Little 903
Bobbie Chapman 403
Nicolas Singleton 203
Dale Barton 901
Aaron Dennis 305
Santos Andrews 504
Jacqueline Neal 102
[root@centosLocal Documents]#
What if wanted to save the results? Pretty easy using redirection.
[root@centosLocal Documents]# tr [:] [\\t] < names.txt >> tabbedNames.txt
[root@centosLocal Documents]# cat tabbedNames.txt
Ted Daniel 101
Jenny Colon 608
Dana Maxwell 602
Marian Little 903
Bobbie Chapman 403
Nicolas Singleton 203
[root@centosLocal Documents]#
Let’s use the -s or squeeze option on poorly formatted text −
[root@centosLocal Documents]# cat lines.txt
line 1
line 2
line 3
line 4
line 5
[root@centosLocal Documents]# tr -s [:blank:] ‘ ‘ < lines.txt >> linesFormat.txt
[root@centosLocal Documents]# cat linesFormat.txt
line 1
line 2
line 3
line 4
line 5
[root@centosLocal Documents]#