`tr` command¶

The tr command is very useful command in deleteing or replaceing character

Replace Newline with Comma¶

Let starts a new session and assigns it a name:

cat <<EOF > test.txt
c1 c2 c3 c4 
1 2 3 4
1 2 3 4
1 2 3 4
EOF

Run cat test.txt | tr -s '\n' ',', the -s flag determina what you wan to replace, here we interestted in new line \n

% cat test.txt | tr -s '\n' ','
c1 c2 c3 c4 ,1 2 3 4,1 2 3 4,1 2 3 4,%

We use tr -s ' ' to convert any repeated spaces into a single space:

cat <<EOF > test2.txt
c1 c2 c3    c4 
1 2 3 4
1 2 3 4
1 2 3 4
EOF

cat test.txt | tr -s ' '

$ cat   test2.txt
c1 c2 c3    c4 
1 2 3 4
1 2 3 4
1 2 3 4
$ cat test.txt | tr -s ' '
c1 c2 c3 c4 
1 2 3 4
1 2 3 4
1 2 3 4
samamiri@beluga1:~$

$ cat test.txt | tr  "c1" "C5"
C5 C2 C3 C4 
5 2 3 4
5 2 3 4
5 2 3 4

Let drop the digitals from file

 cat test.txt | tr -d [:digit:]
c c c c

Or invertly keep the digital

 cat test.txt | tr -cd [:digit:]
 1234123412341234

To convert characters from lower case to upper case, you can either specify a range of characters or use the predefined character classes.

echo "hello" | tr [:lower:] [:upper:]
HELLO
echo "Hello" | tr [:upper:] [:lower:] 
hello