How do I check if a variable contains characters (regex) other than 0-9a-z and - in pure bash?
I need a conditional check. If the string contains characters other than the accepted characters above simply exit 1.
3 Answers
One way of doing it is using the grep command, like this:
grep -qv "[^0-9a-z-]" <<< $STRING
Then you ask for the grep returned value with the following:
if [ ! $? -eq 0 ]; then
echo "Wrong string"
exit 1
fi
As @mpapis pointed out, you can simplify the above expression it to:
grep -qv "[^0-9a-z-]" <<< $STRING || exit 1
Also you can use the bash =~ operator, like this:
if [[ ! "$STRING" =~ [^0-9a-z-] ]] ; then
echo "Valid";
else
echo "Not valid";
fi
4 Comments
mpapis
you can also
grep ... || exit 1
Justin
Do I need to escape the
- in [^0-9a-z-], so [^0-9a-z\-]? Also, isn't the first case echo "Not valid" instead of echo "Valid".
dinox0r
No, you don't need to escape the
- (not even in the grep solution), the first case should be Valid because the conditional is negated (using the ! operator before the regex test), the condition ask if $STRING contains a character that is not a digit, - or a letter, if this evaluates to false ($STRING contains only letters, digits and/or -) the negation turns the evaluation true
tripleee
Tangentially, see also Why is testing “$?” to see if a command succeeded or not, an anti-pattern?
case has support for matching:
case "$string" in
(+(-[[:alnum:]-])) true ;;
(*) exit 1 ;;
esac
the format is not pure regexp, but it works faster then separate process with grep - which is important if you would have multiple checks.
1 Comment
tripleee
case supports glob patterns, not regular expressions. The example uses extended glob patterns, which are often not enabled out of the box. But if your needs are simple, glob patterns are simpler to write and understand, and quite possibly faster to process than regular expressions.Using Bash's substitution engine to test if $foo contains $bar
bar='[^0-9a-z-]'
if [ -n "$foo" -a -z "${foo/*$bar*}" ] ; then
echo exit 1
fi
if [[ "$string" =~ [^a-z0-9-] ]]; then exit 1; else echo all fine; fi