Remove non printing chars from bash variable

Question

I have some variable $a. This variable have non printing characters (carriage return ^M).

>echo $a
some words for compgen
>a+="END"
>echo $a
ENDe words for compgen

How I can remove that char? I know that echo "$a" display it correct. But it's not a solution in my case.

Answer 1

You could use tr:

tr -dc '[[:print:]]' <<< "$var"

would remove non-printable character from $var.

$ foo=$'abc\rdef'
$ echo "$foo"
def
$ tr -dc '[[:print:]]' <<< "$foo"
abcdef
$ foo=$(tr -dc '[[:print:]]' <<< "$foo")
$ echo "$foo"
abcdef

Answer 2

To remove just the trailing carriage return from a, use

a=${a%$'\r'}

Answer 3

I was trying to send a notification via libnotify, with content that may contain unprintable characters. The existing solutions did not quite work for me (using a whitelist of characters using tr works, but strips any multi-byte characters).

Here is what worked, while passing the 💩 test:

message=$(iconv --from-code=UTF-8 -c <<< "$message")

Answer 4

As an equivalent to the tr approach using only shell builtins:

cleanVar=${var//[![:print:]]/}

...substituting :print: with the character class you want to keep, if appropriate.