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Operating Systems Linux Ubuntu Bash to ash port, character-matching problem Post 302910165 by Don Cragun on Tuesday 22nd of July 2014 10:48:37 PM
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

 

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RBASH(1)						      General Commands Manual							  RBASH(1)

NAME
rbash - restricted bash, see bash(1) RESTRICTED SHELL
If bash is started with the name rbash, or the -r option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environment more controlled than the standard shell. It behaves identically to bash with the exception that the follow- ing are disallowed or not performed: o changing directories with cd o setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV o specifying command names containing / o specifying a file name containing a / as an argument to the . builtin command o specifying a filename containing a slash as an argument to the -p option to the hash builtin command o importing function definitions from the shell environment at startup o parsing the value of SHELLOPTS from the shell environment at startup o redirecting output using the >, >|, <>, >&, &>, and >> redirection operators o using the exec builtin command to replace the shell with another command o adding or deleting builtin commands with the -f and -d options to the enable builtin command o using the enable builtin command to enable disabled shell builtins o specifying the -p option to the command builtin command o turning off restricted mode with set +r or set +o restricted. These restrictions are enforced after any startup files are read. When a command that is found to be a shell script is executed, rbash turns off any restrictions in the shell spawned to execute the script. SEE ALSO
bash(1) GNU Bash-4.0 2004 Apr 20 RBASH(1)
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