Extract substring before dot

Question

I try to substract the first string before a dot (.) in bash.

For instance:

1.2.3 -> 1
11.4.1 -> 11

I used the following command based on the docs:

s=4.5.0
echo "${s%.*}"

But it ouptuts 4.5 instead of 4. I don't get it.

Why is that?

Answer 1

You need to use %% to remove the longest match from the end:

$ echo "${s%%.*}"
4

From the docs:

${parameter%%word}
Remove Largest Suffix Pattern. The word shall be expanded to produce a pattern. The parameter expansion shall then result in parameter, with the largest portion of the suffix matched by the pattern deleted.

Answer 2

You can also use the bash Regular Expressions feature built-in in the recent versions of the shell (since bash 3.0), using the tilde(=~) operator.

$ string="s=4.5.0"
$ [[ $string =~ =([[:alnum:]]+).(.*) ]] && printf "%s\n" "${BASH_REMATCH[1]}"
4
$ string="s=32.5.0"
$ [[ $string =~ =([[:alnum:]]+).(.*) ]] && printf "%s\n" "${BASH_REMATCH[1]}"
32