understanding .sh file terminology and cmake

Question

I am trying to use cmake and OpenGL to learn computer graphics, and the tutorial included a run.sh file that is supposed to compile/build the cpp programs. Here is the code:

#!/bin/bash
#calls cd build 
#cmake .. -DSRC<argument> && make argument

EMBEDDED=`echo $2`
DIRECTORY=`echo $1 |cut -d'/' -f1`
FILENAME=`echo $1 |cut -d'/' -f2 |cut -d'.' -f1 | sed -e "s|/|_|g"`
TARGET=${FILENAME}

mkdir build
cd build
rm bin/${TARGET}
cmake .. -DSRC=../$1
make VERBOSE=1
bin/${TARGET}

From my understanding, mkdir creates a build directory, then we 'cd' into that directory, remove something from the previous build, cmake the actual file, I have no idea what make "VERBOSE=1" does, and then I am thinking we access the executable in the last line.

I do not understand what the middle block of code that starts with EMBEDDED does, neither am I sure about what the third comment "#cmake ..." does. I am using cpp files, and I think I have to pass the file as a command line argument along with ./run.sh.

Answer 1

overly complicated assignment

EMBEDDED=`echo $2`

This takes the second argument to the script and performs a split and a glob on it (surprise!) and passes the result of that to echo and then assigns the result of whatever echo does (which, owing to creeping featurism, may not be an echo) to EMBEDDED. This is probably more sensibly written using a simple

EMBEDDED=$2

assignment statement.

overly complicated file path component determination

DIRECTORY=`echo $1 |cut -d'/' -f1`

This could be more intentfully written using the dirname(1) command with also "" to eliminate the POSIX split and glob as one probably does not want whatever results from the (surprise!) split and glob gunking up what gets assigned to DIRECTORY.

DIRECTORY=`dirname "$1"`

However, dirname and cut -d'/' -f1 are not the same unless the only input is somedirectory/somefile. Someone would need to understand the inputs to the code to know whether the simplification to dirname can be made. The expected inputs are not documented in the script posted in the question—are they documented anywhere?

On a related note there is a basename(1) command that may help with

FILENAME=`echo $1 |cut -d'/' -f2 |cut -d'.' -f1 | sed -e "s|/|_|g"`

though it appears this pipeline with cut -d'.' -f1 attempts to obtain a prefix from prefix.whatever, and I have no idea what the sed -e "s|/|_|g" is for, as / cannot appear in filenames. If there are _ in the argument being passed it would be more sensible to pass them as _ and not add extra code to change / into _. So probably the above could be simplified to

FILENAME=`basename "$1" | cut -d'.' -f1`

needlessly dangerous commands

mkdir build
cd build
rm bin/${TARGET}

This sequence may or may not create a build directory and then will try to delete various things from either the new build directory or on failure the parent of that. This is sloppy and indeterminate. And by various things I mean that ${TARGET} will be expanded with the POSIX shell split and glob so may contain quite unexpected filenames—luckily the rm is not the usual "oh yeah, about that filesystem you just lost" rm -rf so the hilarity will be limited to various (still surprising!) filenames, possibly from the wrong directory.

(Some might argue that configuration management or at least guarded commands should be used instead of fragile and error prone shell scripts, but here we are...)

[ -d build ] || { mkdir build; [ -d build ] || exit 1; }
cd build || exit 1
rm bin/"${TARGET}"
cmake .. -DSRC=../"$1" && make VERBOSE=1 && bin/"${TARGET}"

Here build is a directory, is made as a directory, or failing that the script bails (you could also add a custom error message though mkdir typically makes noise). This is not atomic in that something else could touch build between the -d check and subsequent mkdir, so another approach is to "make the directory and then inspect the result to see whether it was a failure (not ok) or EEXIST on a directory (ok). cd is also checked for failures, and $TARGET quoted to prevent the POSIX split and glob thing.