I would like to check the local version of Hugo.
$ hugo version
Hugo Static Site Generator v0.49 linux/amd64 BuildDate: 2018-09-24T10:03:17Z
What would be a safe and future-proof method to extract v0.49 from the output above with a bash script?
Maybe you're better off using grep like this:
$ hugo version
Hugo Static Site Generator v0.59.0-DEV/extended linux/amd64 BuildDate: unknown
$ version=v0.59
$ hugo version | grep -q "${version//./\\.}" && echo "correct version"
correct version
$ version=v0.43
$ hugo version | grep -q "${version//./\\.}" || echo "incorrect version"
incorrect version
grep -q exits successfully if the regex matches, so can be used with shell conditional constructs. I am using a parameter expansion to replace . with \., so that the version number can be used in a regular expression (otherwise the . would match any character).
The bash docs explain how parameter expansion works (see ${parameter/pattern/string}). Basically, ${version//./\\.} globally (/) replaces a . with a \.. Two \ are required in the replacement string, because the first one escapes the second one.
"${version//./\\.}" for someone who is unfamiliar with bash.
A sed expression can be fairly general and still work so long as you version remains in the form of
v[any number of digits].[any number of digits]
To use sed, you can simply pipe the output of hugo version to your sed expression, e.g.
$ hugo version | sed 's/^.*\(v[0-9][0-9]*[.][0-9][0-9]*\).*$/\1/'
Example Use/Output
With your output that would result in:
$ hugo version | sed 's/^.*\(v[0-9][0-9]*[.][0-9][0-9]*\).*$/\1/'
v0.49
You can capture the result in a variable using command substitution, e.g.
hversion=$(hugo version | sed 's/^.*\(v[0-9][0-9]*[.][0-9][0-9]*\).*$/\1/')
Explanation of sed Expression
The breakdown of the sed expression is the normal substitution s/find/replace/ where:
find is:
^.* - and number of characters from the beginning,\( - begin a capture group to save what follows,v - the character 'v',[0-9][0-9]* - at least 1 digit followed by zero or more digits,[.] - a decimal point (or period), followed by[0-9][0-9]* - at least 1 digit followed by zero or more digits,\) - end the capture group saving the captured content,.*$ - all characters to the end of the string.replace is:
\1 a single backreference to the text from the first capture group.That is the extent of it. A normal substitution using a single backreference which will work the same for v0.49 as it will for v243.871.
I'd probably use Bash's builtin read like this:
read -r _ _ _ _ hugo_version _ < <(hugo version)
hugoyou can't guarantee that anything would be future-proof.hugo versionon my system isHugo Static Site Generator v0.59.0-DEV/extended linux/amd64 BuildDate: unknown, so you might want to be careful with any solutions posted here.