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.

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]#