This topic is about Linux Admin – tr Command.
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 single occurrence in SET2 |
| [:alnum:] | Alpha numeric 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 keep 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 caracters into uppper 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]#
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