I need help with how to compare bash variable to a specific format.
i will read user input with read command
for example:
MyComputer:~/Home$ read interface
eth1
MyComputer:~/Home$ echo $interface
eth1
Now i need to check if "$interface" variable with IF loop(it should have "eth" in beginning and should contains numbers 0-9):
if [[ $interface=^eth[0-9] ]]
then
echo "It looks like an interface name"
fi
Thanks in advance
You can use regular expressions for this:
if [[ $interface =~ ^eth[0-9]+$ ]]
then
...
fi
if [[ $interface =~ ^eth[0-9]+$ ]] however could you please explain use of ~ and +$ in bash
=~ is the matching operator and + says that the stuff in the former [] should appear 1 or more times. I think the [[ ]] style isn't portable so one should avoid this?!You can use bash's globs for this:
if [[ $interface = eth+([[:digit:]]) ]]; then
echo "It looks like an interface name"
fi
(avoiding regexps removes one problem). Oh, and mind the spaces around the = sign, and also before and after [[ and ]].
You could use bash V3+ operator =~ as Andrew Logvinov said :
[[ $interface =~ ^eth[0-9]+$ ]] && # ...
Or :
if [[ $interface =~ ^eth[0-9]+$ ]]; then
# ...
fi
Otherwise, you could use too egrep or grep -E (which is useful with older shells like sh...) :
echo "$interface"|egrep "^eth[0-9]+$" > /dev/null && # ...
Or :
if echo "$interface"|egrep "^eth[0-9]+$" > /dev/null; then
# ...
fi
