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Bash to ash port, character-matching problem

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Operating Systems Linux Ubuntu Bash to ash port, character-matching problem
# 1  
Old 07-22-2014
Bash to ash port, character-matching problem
I'm trying to convert this working bash script into an Ash script,

Code:
 read -p "Username:" _username
   if ! [[ "$_username" =~ [^a-zA-Z0-9] ]]; then
   	 echo "Valid"
   else
    	 echo "INVALID"
   fi

However, Ash does not recognize the "=~" character.

How can I do this?
Also, is there a good reference guide, so I don't need to post all my questions here? I can't find anything!

Moderator's Comments:
Mod Comment edit by bakunin: please use the CODE-tags for code and/or terminal output. Thank you.

Furthermore, please place different questions into different threads. It is perfectly OK to open several threads for several distinct problems and i can assure you, we have empty threads in abundance, without any threat of a shortage.
Last edited by bakunin; 07-23-2014 at 11:36 AM..
# 2  
Old 07-22-2014
The bash shell provides lots of extensions above and beyond what the POSIX standards require. The ash shell doesn't provide nearly as many extensions. If you use the standard as your shell programming guide, you should get by OK. A straight translation (getting rid of bash extensions) for your script would be:
Code:
printf "Username:"
read _username
if [ "$_username" = "${_username%[^a-zA-Z0-9]*}" ]
then    echo "Valid"
else    echo "INVALID"
fi

If your system allows alphanumeric characters other than characters in the Portable Filename Character Set in user names, you might want:
Code:
printf "Username:"
read _username
if [ "$_username" = "${_username%[^[:album:]]*}" ]
then    echo "Valid"
else    echo "INVALID"
fi

# 3  
Old 07-23-2014
Hi.

This may be useful ... cheers, drl

checkbashisms | Free Development software downloads at SourceForge.net
# 4  
Old 07-23-2014
I'd like to add that in any case, letting variable names start with underscores is a problematic practice, even if it is allowed. Consider:

Code:
_foo="bar"
echo $_foo

_="bar"
echo $_

I hope this helps.

bakunin
# 5  
Old 07-23-2014
Code:
printf "Username:"; read _username
   if [[ "$_username" != *[!a-zA-Z0-9]* ]]; then
      echo "Valid"
   else
      echo "INVALID"
   fi

Last edited by MadeInGermany; 07-23-2014 at 12:55 PM.. Reason: [^ ] replaced by [! ]
# 6  
Old 07-23-2014
A case statement will work in any Bourne type shell. This also makes it easy to test for an empty variable..
Code:
printf "Username: "
read _username
case $_username in 
  (*[![:alnum:]]*|"") 
    echo "invalid" ;;
  (*) 
    echo "valid"
esac

Note that will also allow letters with accents like é and ã
To exclude those, you could use (*[!a-zA-Z0-9]*|"") but that may not work properly because of a locale collation order...

--
Also note hat the proper negation character with character sets used in patterns is ! not ^ (even though it probably will work too)
Last edited by Scrutinizer; 07-23-2014 at 02:34 PM..
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