Linux shell tr command details

Linux shell tr command details

1. Use

tr, short for translate, is used to compress duplicate characters, delete control characters in files, and perform character conversion operations.

2. Grammar

tr [OPTION]... SET1 [SET2]

3. The parameters

3.1 -s compressed duplicate characters

replace each input sequence of character repeated is SET1 with with occurrence occurrence that character

xiaosi@Qunar:~/test$ echo "aaabbbaacccfddd" | tr -s [abcdf] // abacfd

You can use this feature to delete the blank lines in the file, essentially replacing the corresponding duplicate characters with the characters specified by SET1, as shown in figure 1 above

xiaosi@Qunar:~/test$ cat b.txt
I like football
Football is very fun!
Hello
xiaosi@Qunar:~/test$ cat b.txt | tr -s ["\n"]
I like football
Football is very fun!
Hello

3.2 -d delete characters

-d: delete, delete all characters specified in SET1, do not convert (delete characters in SET1, do not translate)

xiaosi@Qunar:~/test$ echo "a12HJ13fdaADff" | tr -d "[a-z][A-Z]"
1213
xiaosi@Qunar:~/test$ echo "a1213fdasf" | tr -d [adfs]
1213

3.3 character substitution

-t: truncate, replace the characters in SET1 with the characters corresponding to SET2, and the default value of 1 is -t

xiaosi@Qunar:~/test$ echo "a1213fdasf" | tr -t [afd] [AFO] // A1213FOAsF

The code above converts a to A, f to F, and d to O.

Can use this 1 characteristic, realizes the size letter conversion

xiaosi@Qunar:~/test$ echo "Hello World I Love You" |tr -t [a-z] [A-Z]
HELLO WORLD I LOVE YOU
xiaosi@Qunar:~/test$ echo "HELLO WORLD I LOVE YOU" |tr -t [A-Z] [a-z]
hello world i love you

You can also use character sets for conversion

xiaosi@Qunar:~/test$ echo "Hello World I Love You" |tr -t [:lower:] [:upper:]
HELLO WORLD I LOVE YOU
xiaosi@Qunar:~/test$ echo "HELLO WORLD I LOVE YOU" |tr -t [:upper:] [:lower:]
hello world i love you

Remark:

The set of characters is as follows

\NNN 8 Character of base value  NNN (1 to 3  for 8 Character of base value )
\\  The backslash 
\a Ctrl-G  The bell 
\b Ctrl-H  Back space 
\f Ctrl-L  The left page breaks 
\n Ctrl-J  A new row 
\r Ctrl-M  enter 
\t Ctrl-I tab key 
\v Ctrl-X  Horizontal tabs 
CHAR1-CHAR2  from CHAR1  to  CHAR2 All characters according to ASCII Sequence of characters 
[CHAR*] in SET2, copies of CHAR until length of SET1
[CHAR*REPEAT] REPEAT copies of CHAR, REPEAT octal if starting with 0
[:alnum:]  All the letters and Numbers 
[:alpha:]  All the letters 
[:blank:]  Horizontal tabs, whitespace, etc 
[:cntrl:]  All control characters 
[:digit:]  All the Numbers 
[:graph:]  All printable characters, excluding Spaces 
[:lower:]  All lowercase characters 
[:print:]  All printable characters, including Spaces 
[:punct:]  All punctuation characters 
[:space:]  All horizontal or vertical white space 
[:upper:]  All capital letters 

3.4 character complement substitution

-c: complement, replacing characters not included in SET1 with SET2

xiaosi@Qunar:~/test$ cat a.txt
Monday   09:00
Tuesday  09:10
Wednesday 10:11
Thursday  11:30
Friday   08:00
Saturday  07:40
Sunday   10:00
xiaosi@Qunar:~/test$ cat a.txt | tr -c "[a-z][A-Z]" "#" | tr -s "#" | tr -t "#" "\n"
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Sunday

In the code above, tr-c "[a-z][A-Z]" "#" indicates that all characters except the size letters are replaced with #.

The above code can be optimized as:

xiaosi@Qunar:~/test$ cat a.txt | tr -cs "[a-z][A-Z]" "\n"
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Sunday

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