linux - simplify semantic versioning script - linux

Question

I have semantic versioning for an app component and this is how I update the major version number and then store it back in version.txt. This seems like a lot of lines for a simple operation. Could someone please help me trim this down? No use of bc as the docker python image I'm on doesn't seem to have that command.
This is extracted from a yml file and version.txt only contains a major and minor number. 1.3 for example. The code below updates only the major number (1) and resets the minor number to 0. So if I ran the code on 1.3, I would get 2.
- echo $(<version.txt) 1 | awk '{print $1 + $2}' > version.txt
VERSION=$(<version.txt)
VERSION=${VERSION%.*}
echo $VERSION > version.txt
echo "New version = $(<version.txt)"

Answer 1

About Simplicity
"Simple" and "short" are not the same thing. echo $foo is shorter than echo "$foo", but it actually does far more things: It splits the value of foo apart on characters in IFS, evaluates each result of that split as a glob expression, and then recombines them.
Similarly, making your code simpler -- as in, limiting the number of steps in the process it goes through -- is not at all the same thing as making it shorter.
Incrementing One Piece, Leaving Others Unmodified
if IFS=. read -r major rest <version.txt || [ -n "$major" ]; then
echo "$((major + 1)).$rest" >"version.txt.$$" && mv "version.txt.$$" version.txt
else
echo "ERROR: Unable to read version number from version.txt" >&2
exit 1
fi
Incrementing Major Version, Discarding Others
if IFS=. read -r major rest <version.txt || [ -n "$major" ]; then
echo "$((major + 1))" >"version.txt.$$" && mv "version.txt.$$" "version.txt"
else
echo "ERROR: Unable to read version number from version.txt" >&2
exit 1
fi
Rationale
Both of the above are POSIX-compliant, and avoid relying on any capabilities not built into the shell.
IFS=. read -r first second third <input reads the first line of input, and splits it on .s into the shell variables first, second and third; notably, the third column in this example includes everything after the first two, so if you had a.b.c.d.e.f, you would get first=a; second=b; third=d.e.f -- hence the name rest to make this clear. See BashFAQ #1 for a detailed explanation.
$(( ... )) creates an arithmetic context in all POSIX-compliant shells. It's only useful for integer math, but since we split the pieces out with the read, we only need integer math. See http://wiki.bash-hackers.org/syntax/arith_expr
Writing to version.txt.$$ and renaming if that write is successful prevents version.txt from being left empty or corrupt if a failure takes place between the open and the write. (A version that was worried about symlink attacks would use mktemp, instead of relying on $$ to generate a unique tempfile name).
Proceeding through to the write only if the read succeeds or [ -n "$major" ] is true prevents the code from resetting the version to 1 (by adding 1 to an empty string, which evaluates in an arithmetic context as 0) if the read fails.