Removing all special characters from a string in Bash

Question

I have a lot of text in lowercase, only problem is, that there is a lot of special characters, which I want to remove it all with numbers too.

Next command it's not strong enough:

tr -cd '[alpha]\n '

In case of éćščž and some others it returns "?" But I want to remove all of them. Is there any stronger command?

I use linux mint 4.3.8(1)-release

Answer 1

You can use tr to print only the printable characters from a string like below. Just use the below command on your input file.

tr -cd "[:print:]\n" < file1   

The flag -d is meant to the delete the character sets defined in the arguments on the input stream, and -c is for complementing those (invert what's provided). So without -c the command would delete all printable characters from the input stream and using it complements it by removing the non-printable characters. We also keep the newline character \n to preserve the line endings in the input file. Removing it would just produce the final output in one big line.

The [:print:] is just a POSIX bracket expression which is a combination of expressions [:alnum:], [:punct:] and space. The [:alnum:] is same as [0-9A-Za-z] and [:punct:] includes characters ! " # $ % & ' ( ) * + , - . / : ; < = > ? @ [ \ ] ^ _ ` { | } ~

Answer 2

I am not exactly certain where the text is coming from in your question but lets just say that the "lot of text in lowercase" is in the file called special.txt you could do something like the following but focused more on the characters you want to keep:

cat special.txt | sed 's/[^a-z  A-Z]//g'

It is a bit like doing surgery with an axe though.

Another possible solution in the post Remove non-ascii characters from ...

If the above don't solve your question, please try to provide a bit more details and I might be able to provide a more actionable answer.