Remove numbers (strip numeric characters) from the string variable

Question

I want to strip all numeric characters from a String variable, eg from:

VARIABLE=qwe123rty567

to:

echo $VARIABLE
> qwerty

I've searched many posts but they either use sed to output to file/file names, or output to echo. I was not able to get it working with because of the white space:

VARIABLE=$VARIABLE | sed 's/[0-9]*//g'

Answer 1

With bash:

$ printf '%s\n' "${VARIABLE//[[:digit:]]/}"
qwerty

[:digit:] can contain other characters than 0 to 9 depend on your locale. If you want only to remove 0 to 9, use C locale instead.

Answer 2

For variety, here's methods using

tr:

VARIABLE=$(printf '%s' "$VARIABLE" | tr -d '0123456789')

sed:

VARIABLE=$(printf '%s' "$VARIABLE" | sed 's/[0-9]//g')

Bash expansion, by far the most terse:

VARIABLE=${VARIABLE//[0-9]/}

and finally Bash expansion again, this time using the [[:digit:]] character class.

VARIABLE=${VARIABLE//[[:digit:]]/} 

Note that (as others have pointed out) [[:digit:]], should cover anything defined as a digit in your locale.

Answer 3

VARIABLE=qwe123rty567
IFS=0123456789
set -f # Disable glob
printf %s $VARIABLE

---

qwerty

further manipulation is possible.

VARIABLE=qwe123rty567
IFS=0123456789
set -f # Disable glob
set -- $VARIABLE
IFS=;   VARIABLE=$*
printf "replaced $# numbers in \$VARIABLE. RESULT:\t%s\n" "$*"

---

replaced 6 numbers in $VARIABLE. RESULT:    qwerty

Answer 4

White space (actually, failure to quote your variables) was only part of the problem.

You can't just pipe a variable through sed like that, it doesn't work. More precisely, it doesn't pipe the value of "$VARIABLE" through sed, the shell will try to execute the value of "$VARIABLE" and pipe the output of that through sed. BTW, this is not a bug - this is useful if $VARIABLE happens to contain a valid command like ls or rsync or whatever.

Also, if you want to assign the ouput of a command or pipeline to a variable, you need to surround that command/pipeline with $().

So, to modify a variable with sed, you need to do something like this:

VARIABLE=$(printf '%s' "$VARIABLE" | sed 's/[0-9]*//g')

You could use echo there instead of printf but echo will interpret and act on certain character sequences in $VARIABLE (e.g. \t, \n, \r, etc), while printf won't. You'll run across a lot of examples using echo...replace them with printf '%s', it's much safer.