Shell script to download and extract a tarball from GitHub

I don't want anything to execute if any preceding step fails:

#!/bin/sh

file="v0.9"
renamed=$file".tar.gz"
dir="utils/external/firepython/"
location="https://github.com/darwin/firepython/tarball/$file"

wget --no-check-certificate $location --output-document=$renamed && \
mkdir -p $dir && \
gunzip $renamed && \
echo "extracting to $dir" && \
tar xf $file".tar" --directory $dir --strip-components 1 && \
echo "Cleaning up..." && \
rm -r $file".tar" && \
echo "Done"

You're looking for set -e. From POSIX:


-e
When this option is on, if a simple command fails for any of the reasons listed in Consequences of Shell Errors or returns an exit status value >0, and is not part of the compound list following a while, until, or if keyword, and is not a part of an AND or OR list, and is not a pipeline preceded by the ! reserved word, then the shell shall immediately exit.

In other words, plain commands cause the shell to exit if they fail. (You can use something like command || true to allow command to return nonzero.) If you need to perform some cleanup, you can set a trap for the EXIT pseudo-signal.

And better double-quote all your variable expansions. That way your script won't fail horribly if you ever point it at a directory or an URL containing ? or * or a space.

dry -r
wget --no-check-certificate "$location" --output-document="$renamed"
mkdir -p "$dir"
gunzip "$renamed"
echo "extracting to $dir"
tar xf "$file.tar" --directory "$dir" --strip-components 1
echo "Cleaning up..."
rm -r "$file.tar"
echo "Done"

Another useful shell idiom to pass optional arguments to a shell script without hassle is to set variables only if they're unset. That way you can pass arguments through the environment, e.g. file=v0.9.1 myscript.

: "${file=v0.9}"
: "${renamed=$file.tar.gz}"
: "${dir=utils/external/firepython/}"
: "${location=https://github.com/darwin/firepython/tarball/$file}"

StackExchange Code Review Q#1766, answer score: 16