Shell Programming and Scripting

# cat myfile
Bb2$£¤µ%§\°~`!@#$%^&*()_-+={[}]|:;"'<,>.?/
# a="@#+="
# sed 's/[^'$a'[:alnum:]]*//g' myfile
Bb2µ@#+=
#

# a="#@|_%"
# sed 's/[^'$a'[:alnum:]]*//g' myfile
Bb2µ%@#%_|
#

sed 's/[^'$a'" "[:alnum:]]*//g' ${a[j]} > revised.txt

sed 's/[^'$a'[:space:][:alnum:]]*//g' myfile

sed 's/[^'$a' [:alnum:]]*//g' myfile

sed 's/[^'${a// /}' [:alnum:]]*//g' myfile

$ a="# @ %"
$ echo $a
# @ %
$ echo ${a// /}
#@%
$ sed 's/[^'$a'[:space:][:alnum:]]*//g' myfile
sed: -e expression n°1, caractère 5: Commande `s' inachevée
$ sed 's/[^'${a// /}'[:space:][:alnum:]]*//g' myfile
Bb2µ%@ #%
$

a='list' # The variable a specifies the set of punctuation characters that are not to be deleted.
sed 's/[^'$a' [:alnum:][:space:][:cntrl:]]*//g'