Understanding Linux / UNIX tr command

last updated December 23, 2007 in BASH Shell, CentOS, Debian / Ubuntu, HP-UX Unix, Linux, OpenBSD, RedHat and Friends, Suse, Ubuntu Linux, UNIX

Q. Can you explain the tr command and how to use it under Linux / UNIX like oses?

tr command syntax

tr [options] "set1" "set2" echo something | tr "set1" "set2" tr "set1" "set2" < input.txt tr "set1" "set2" < input.txt > output.txt

How do I use tr command under Linux / UNIX?

Translate the word ‘linux’ to upper-case:
$ echo 'linux' | tr "[:lower:]" "[:upper:]" $ echo 'linux' | tr "a-z" "A-Z" $ echo 'I LovE linuX. one is better Than 2' | tr "a-z" "A-Z"
Output:

LINUX
I LOVE LINUX. ONE IS BETTER THAN 2

Create a list of the words in /path/to/file, one per line, enter:
$ tr -cs "[:alpha:]" "\n" < /path/to/file
Where,

-c : Complement the set of characters in string1
-s : Replace each input sequence of a repeated character that is listed in SET1 with a single occurrence of that character

Shell scripting example

In the following example you will get confirmation before deleting the file. If the user responds in lower case, the tr command will do nothing, but if the user responds in upper case, the character will be changed to lower case. This will ensure that even if user responds with YES, YeS, YEs etc; script should remove file:

#!/bin/bash
echo -n "Enter file name : "
read myfile
echo -n "Are you sure ( yes or no ) ? "
read confirmation
confirmation="$(echo ${confirmation} | tr 'A-Z' 'a-z')"
if [ "$confirmation" == "yes" ]; then
   [ -f $myfile ] &&  /bin/rm $myfile || echo "Error - file $myfile not found"
else
   : # do nothing
fi

Remove all non-printable characters from myfile.txt
$ tr -cd "[:print:]" < myfile.txt

Remove all two more successive blank spaces from a copy of the text in a file called input.txt and save output to a new file called output.txt
tr -s ' ' ' ' < input.txt > output.txt

The -d option is used to delete every instance of the string (i.e., sequence of characters) specified in set1. For example, the following would remove every instance of the word nameserver from a copy of the text in a file called /etc/resolv.conf and write the output to a file called ns.ipaddress.txt:
tr -d 'nameserver' < /etc/resolv.conf > ns.ipaddress.txt

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.

33 comment

Planet Lowyat says:
December 23, 2007 at 3:48 pm
Great tips. Typo error -> prodcued
Reply
Marko says:
February 13, 2008 at 3:08 pm
tr -d ‘nameserver’ ns.ipaddress.txt
I think this would delete the word nameserver, but also all occurrences of characters from set {nameserver}, which could probably create big mess.
Proper command should be:
sed ‘s/nameserver//g’ ns.ipaddress.txt
Reply
1. Sergei says:
  September 14, 2014 at 1:18 pm
  Right on.
  Reply
Maher says:
August 23, 2008 at 11:10 am
can you give scripts for these :
Exercise 1: Write a shell script (named checkfiles.sh) that lists
all text files “*.TXT” in a directory and writes the first line of each text-file to a file called Text_Heads.
Exercise 2: Write a shell script (called words-no.sh) that counts the number of distinct words in a text file given as Argument.
Remark: White space characters are spaces, tabs, form feeds, and new lines. Use the tr, sort, grep. wc.
Exercise 3: Write a shell script (called cleancore.sh) that removes unwanted files from a directory and its subdirectories.
Argument 1 is the directory where to start the search. It defaults to your home directory (If there is no directory by this name).
Argument 2 after the directory is standard file-name that match the files that are to be removed, it defaults is ‘core’.
Reply
1. Sara says:
  April 30, 2012 at 2:26 am
  No. Do your homework by yourself.
  Reply
heba says:
September 1, 2008 at 11:45 am
How can I get the Exercises solve??
Please help me
Reply
laoa says:
September 10, 2008 at 11:02 am
Is there any way to do the following questions
1. Replace many different chars with one same char
ab(cde)fg -> ab~cde~fg
echo ab(cde)fg | tr “()” “~~”
echo a1234b | tr “[0-9]” “A”
a1234b ### hope aAAAAb
echo a1234b | tr “[0-9]” “AAAA”
aAAA4b
echo a1234b | tr “[0-9]” “AAAAA”
aAAAAb
2. replace one char with two chars
a~b -> a==b
Thanks
Reply
nixCraft says:
September 10, 2008 at 12:21 pm
laoa,
Avoid shell escape, enter:
echo 'ab(cde)fg' | tr "()" "~~"
OR
echo ab\(cde\fg | tr "()" "~~"
Reply
pham van hai says:
November 11, 2008 at 3:39 pm
please help me
convert file in window into file in linux
I try
cat file_linux | tr -s “\n” “\n\r” ?
but it cannot run
Reply
budoliv says:
February 6, 2009 at 10:36 pm
How do you get only the first letter capitalized?
Reply
Chris de Vidal says:
March 6, 2009 at 10:26 pm
pham van hai: Use the unix2dos program instead.
budoliv: I’d suggest you use sed instead but I don’t know the syntax off-hand.
Reply

Hey!

Nice Tutorial. I tried to write a small shell script to rename my mp3-files, but it doesn’t work. What is wrong with it? Can someone help me?

Greets, Andy

for i in "*.[mM][pP]3";
do
        # convert uppercase to lowercase
        $n="$(echo ${i} | tr [:upper:] [:lower:])"

        # replace whitespaces with underscores
        $n="$(echo ${n} | tr [:blank:] '_')"

        # replace dots with underscores
        $n="$(echo ${n} | tr '.' '_')"

        # replace hypens with underscores
        $n="$(echo ${n} | tr '-' '_')"

        # replace multiple underscores
        $n="$(echo ${n} | tr -s '_')"

        # remove numbers at the beginning
        $n="$(echo ${n} | sed 's/^[0-9]*//')"

        # remove underscores at the beginning
        $n="$(echo ${n} | sed 's/^\_//')"

        # correct file ending
        $n="$(echo ${n} | sed 's/\_mp3/\.mp3/')"

        # rename file
        mv -v "$i" "$n";
done

Have you tried rename command to rename multiple files? It also support regex.. Try find command to generate a file list:

find /path/to/dir -iname "*.mp3" -print0 | while read -d $'\0' file; do your-script.sh "$file"; done

Create your-script.sh to rename each file:

#!/bin/sh
       i="$@"
        # convert uppercase to lowercase
        $n="$(echo ${i} | tr [:upper:] [:lower:])"

        # replace whitespaces with underscores
        $n="$(echo ${n} | tr [:blank:] '_')"

        # replace dots with underscores
        $n="$(echo ${n} | tr '.' '_')"

        # replace hypens with underscores
        $n="$(echo ${n} | tr '-' '_')"

        # replace multiple underscores
        $n="$(echo ${n} | tr -s '_')"

        # remove numbers at the beginning
        $n="$(echo ${n} | sed 's/^[0-9]*//')"

        # remove underscores at the beginning
        $n="$(echo ${n} | sed 's/^\_//')"

        # correct file ending
        $n="$(echo ${n} | sed 's/\_mp3/\.mp3/')"

        # rename file
        mv -v "$i" "$n";

HTH

kiran says:
June 30, 2009 at 10:11 am
try this it will work
for i in *.
do
# convert uppercase to lowercase
n=”$(echo ${i} | tr [:lower:] [:upper:])”
# replace whitespaces with underscores
n=”$(echo “${n}” | tr [:blank:] ‘_’)”
# replace dots with underscores
n=”$(echo “${n}” | tr ‘.’ ‘_’)”
# replace hypens with underscores
n=”$(echo “${n}” | tr ‘-‘ ‘_’)”
# replace multiple underscores
n=”$(echo “${n}” | tr -s ‘_’)”
# remove numbers at the beginning
n=”$(echo “${n}” | sed ‘s/^[0-9]*//’)”
# remove underscores at the beginning
n=”$(echo “${n}” | sed ‘s/^\_//’)”
# correct file ending
n=”$(echo “${n}” | sed ‘s/\_mp3/\.mp3/’)”
# rename file
mv -v “$i” “$n”;
done
Reply
Velava says:
June 29, 2010 at 10:48 am
To replace comma’s in .csv file by the single space i used the below script,
tr ‘,’ ‘ ‘ output.csv
After the above script has been executed, its giving the “Unable to Read” error message when i was trying to open the converted file such “output.csv”.
For the small file its not giving any error, but when i m trying to covert the 8mb file it gives the above error message..
Please help me ASAP
thanks in advance
Reply
velava says:
June 29, 2010 at 10:51 am
The script used for the above is,
tr ‘,’ ‘ ‘ output.csv
In the previous comment i did mistake while typing .
Reply
d1t1 says:
March 21, 2011 at 6:46 pm
i have a html file with only a line and i want the output to be only the NAME and the NUMBERS
example:

change output like:
NAME 542103541
Can someone tell me how,! thx in advance!
Reply
d1t1 says:
March 21, 2011 at 6:48 pm
i once tried this but it also isnt too useful:
cat s | tr -cs “[:digit:]” “\n” > s.new0
Reply
pat-r says:
September 13, 2011 at 7:56 pm
I have the following examples:
Input Output
AJ22 0022
aK12 0012
0082 0082
Can somebody post a tr command to accomplish this.
–Thanks
Reply
1. Billy Baroo says:
  November 16, 2011 at 3:19 pm
  Use asterisk in set2 to let set2 & set1 have equal length, e.g.
  echo “AJ22 aK12 0082″|tr ‘[:alpha:]’ ‘[0*]’
  Reply
2. Lynx says:
  February 27, 2014 at 12:25 am
  tr [:alpha:] 0 < filename.txt
  Reply
rajiv says:
November 4, 2011 at 6:30 pm
tr [A-Z][a-z] 0
Reply
pritam says:
September 12, 2012 at 11:14 am
[root@localhost ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda8 40G 4.5G 34G 12% /
tmpfs 2.0G 100K 2.0G 1% /dev/shm
/dev/sda7 485M 39M 421M 9% /boot
/dev/sda9 23G 3.3G 19G 16% /usr
/dev/sda10 23G 323M 22G 2% /var
/dev/mapper/vg1-lv1 3.9M 24K 3.7M 1% /root/pri
/dev/mapper/vg1-lv2 3.9M 24K 3.7M 1% /root/prit
/dev/mapper/vg1-lv3pritampatil
3.9M 24K 3.7M 1% /root/prita
i used awk but still not working…i want to separate “mounted on” column…
but i fell.. here is output what i did…!!! but one more mounted directory nt seen why…????
[root@localhost ~]# df -h | awk -F ” ” ‘{print $6}’
Mounted
/
/dev/shm
/boot
/usr
/var
/root/pri
/root/prit
Reply
Charlie says:
March 24, 2013 at 8:11 pm
Hi,
Can somebody help me to transform this kind of expressions, like 01:22:12:345 into 01:22:12,345, please.
I wrote this expression : tr -s ‘:[0-9][0-9][0-9]’ ‘,[0-9][0-9][0-9]’ but i had all the colons replace by commas. If I erase the -s command, the result is the same.
If somebody can give me an help, thanks.
Reply
vishal says:
March 1, 2014 at 4:40 am
Write shell script that do equivalent to tr ‘is’ ‘are’ utility.
Reply
Sergei says:
September 14, 2014 at 1:21 pm
It’s a great article until:
tr -d ‘nameserver’ ns.ipaddress.txt
is given as an example of how to remove nameserver from /etc/resolv.conf. This should be removed from the article lest somebody does it in production somewhere.
Reply
bob says:
September 30, 2014 at 3:09 pm
Input Output
a?$ ?tg
Translation a?$ / ?tg / ttg
How can I convert back with a second command in script? without using opposing script or aligning both translations.
If in/out abcd/dcba translation works either way.
I could switch in/out with a second script.
Looking for something like
tr a?$ ?tg
maybe && or : with $input or echo tr ?tg a?$ in the same script.
Reply
1. bob says:
  September 30, 2014 at 7:16 pm
  Ex: input1output1 “print” output1output2 “print”
  I’m calling my script from terminal, but unable to pickup the printed output1 with tr2.
  I’m expecting to find a double output.
  Ex:hello/12334/hello or 12334/hello/12334
  Reply
Wanderer says:
October 26, 2014 at 1:51 pm
Thank you :)
Reply
barsita ray says:
May 12, 2015 at 1:45 pm
write a shell program to find the initial of any name and display it using tr commnd.
example:Rabindra NAth Tagore is given as input .
Output will be R.N.Tagore.
I cannot solve this and on friday(15.5.15) I have lab exam on this shell.
Reply
Diego says:
October 22, 2016 at 2:13 pm
Hi, can you explain me why this code doesn’t work ??
$ echo hola que tal 12344 >> file
$ tr "[:alpha:]" "[:upper:]" < file
I want to replace all lower case in the file into upper case.
Thanks
Reply
1. Vivek Gite says:
  October 22, 2016 at 2:56 pm
  $ tr "[:lower:]" "[:upper:]" < file
  Reply
  1. Diego says:
    October 22, 2016 at 3:46 pm
    Thanks, i already now that , is just that can’t explain why my code it’s wrong
    Reply

nixCraft

nixCraft

Understanding Linux / UNIX tr command

tr command syntax

How do I use tr command under Linux / UNIX?

Shell scripting example

Recommended readings:

Posted by: Vivek Gite

33 comment

Leave a Comment Cancel reply

tr command syntax

How do I use tr command under Linux / UNIX?

Shell scripting example

Recommended readings:

Posted by: Vivek Gite

<img class="comments-image" src="https://www.cyberciti.biz/faq/wp-content/themes/cybercity/assets/images/comment.png" title="Comments"> 33 comment

Leave a Comment Cancel reply

33 comment