CODEWITHSUNDEEP
linux
Neon Flash
Neon Flash

Reputation: 3233

Removing Control Characters from a File

I want to delete all the control characters from my file using linux bash commands.

There are some control characters like EOF (0x1A) especially which are causing the problem when I load my file in another software. I want to delete this.

Here is what I have tried so far:

this will list all the control characters:

cat -v -e -t file.txt | head -n 10

^A+^X$
^A1^X$
^D ^_$
^E-^D$
^E-^S$
^E1^V$
^F%^_$
^F-^D$
^F.^_$
^F/^_$
^F4EZ$
^G%$

This will list all the control characters using grep:

$ cat file.txt | head -n 10 | grep '[[:cntrl:]]'
+
1

-
-
1
%
-
.
/

matches the above output of cat command.

Now, I ran the following command to show all lines not containing control characters but it is still showing the same output as above (lines with control characters)

$ cat file.txt | head -n 10 | grep '[^[:cntrl:]]'
+
1

-
-
1
%
-
.
/

here is the output in hex format:

$ cat file.txt | head -n 10 | grep '[[:cntrl:]]' | od -t x2
0000000 2b01 0a18 3101 0a18 2004 0a1f 2d05 0a04
0000020 2d05 0a13 3105 0a16 2506 0a1f 2d06 0a04
0000040 2e06 0a1f 2f06 0a1f
0000050

as you can see, the hex values, 0x01, 0x18 are control characters.

I tried using the tr command to delete the control characters but got an error:

$ cat file.txt | tr -d "\r\n" "[:cntrl:]" >> test.txt
tr: extra operand `[:cntrl:]'
Only one string may be given when deleting without squeezing repeats.
Try `tr --help' for more information.

If I delete all control characters, I will end up deleting the newline and carriage return as well which is used as the newline characters on windows. How do I delete all the control characters keeping only the ones required like "\r\n"?

Thanks.

Upvotes: 35

Views: 59879

Answers (4)

UKMonkey
UKMonkey

Reputation: 6983

A little late to the party: cat -v <file> which I think is the easiest to remember of the lot!

Upvotes: 6

Stephen Boston
Stephen Boston

Reputation: 1189

Based on this answer on unix.stackexchange, this should do the trick:

$ cat scriptfile.raw | col -b > scriptfile.clean

Upvotes: 16

kenorb
kenorb

Reputation: 166389

Try grep, like:

grep -o "[[:print:][:space:]]*" in.txt > out.txt

which will print only alphanumeric characters including punctuation characters and space characters such as tab, newline, vertical tab, form feed, carriage return, and space.

To be less restrictive, and remove only control characters ([:cntrl:]), delete them by:

tr -d "[:cntrl:]"

If you want to keep \n (which is part of [:cntrl:]), then replace it temporarily to something else, e.g.

cat file.txt | tr '\r\n' '\275\276' | tr -d "[:cntrl:]" | tr "\275\276" "\r\n"

Upvotes: 14

Kyle Barbour
Kyle Barbour

Reputation: 1035

Instead of using the predefined [:cntrl:] set, which as you observed includes \n and \r, just list (in octal) the control characters you want to get rid of:

$ tr -d '\000-\011\013\014\016-\037' < file.txt > newfile.txt

Upvotes: 35

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