BASH script to compile multiple C++ files - OpenCV

Question

Please see Call functions in other files in C++ and OpenCV for initial problem. The code I am using is given there in detail. This is a subproblem.

I have a BASH script:

echo "compiling $1"
if [[ $1 == *.c ]]
then
    gcc -ggdb `pkg-config --cflags opencv` -o `basename $1 .c` $1 `pkg-config --libs opencv`;
elif [[ $1 == *.cpp ]]
then
    g++ -ggdb `pkg-config --cflags opencv` -o `basename $1 .cpp` $1 `pkg-config --libs opencv`;
else
    echo "Please compile only .c or .cpp files"
fi
echo "Output file => ${1%.*}"

The above BASH script is used to compile OpenCV code using ./script.sh input.cpp.
My doubt is how can I modify it to compile multiple files at the same time, like another file with some functions I am using in my main code like:
./script.sh input.cpp functions.cpp

---

EDIT
As suggested by John B, I modified my BASH script to

for f in "$@"; do
    echo "compiling $f"
    if [[ $f == *.c ]]
    then
        gcc -ggdb `pkg-config --cflags opencv` -o `basename "$f" .c` "$f" `pkg-config --libs opencv`
    elif [[ $f == *.cpp ]]
    then
        g++ -ggdb `pkg-config --cflags opencv` -o `basename "$f" .cpp` "$f" `pkg-config --libs opencv`
    else
        echo "$f is not .c or .cpp file"
    fi
    echo "Output file => ${f%.*}"
done

But now, I get the following error:

compiling draw_shapes.cpp
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status
Output file => draw_shapes
compiling test.cpp
/tmp/ccW65wuP.o: In function `main':
/home/kanishka/Desktop/opencv test/test.cpp:31: undefined reference to `draw_line(cv::Mat, cv::Point_<int>, cv::Point_<int>, int, int, int)'
collect2: error: ld returned 1 exit status
Output file => test

Answer 1

As Jonathan Leffler suggests, it's better practice to use a makefile. But if you want to use a Bash script, you could call all the arguments with $@ and iterate over each.

for f in "$@"; do
    echo "compiling $f"
    if [[ $f == *.c ]]
    then
        gcc -ggdb `pkg-config --cflags opencv` -o `basename "$f" .c` "$f" `pkg-config --libs opencv`
    elif [[ $f == *.cpp ]]
    then
        g++ -ggdb `pkg-config --cflags opencv` -o `basename "$f" .cpp` "$f" `pkg-config --libs opencv`
    else
        echo "$f is not .c or .cpp file"
    fi
    echo "Output file => ${f%.*}"
done

Answer 2

To problem stated in edit:

To get files compiled when they don't have the "main" function, You will need to use -c switch, so compiler produces objects instead of executables. The proces should look like this:

g++ $src_file1 $src_file2 -Iincludes_directory -c -o obj/object1.o
g++ $src_file3 $src_file4 -Iincludes_directory -c -o obj/object2.o
g++ $src_file5 $src_file6 -Iincludes_directory -c -o obj/object3.o
....
g++ $srcfileX $src_file_containing_main_function -Iincludes_directory -c -o obj/object_with_main.o

When You have the objects done, it is time for linking them together

g++ obj/* -o my_awesome_executable

Answer 3

A straightforward and simplistic solution:

Create another script file with the following content:

./script.sh input.cpp
./script.sh functions.cpp

Then, run it without arguments:

./doit.sh

Your new script, doit.sh, must reside in the same folder as your existing script.sh.

Please consider investing time into learning a decent build system, such as cmake. It could be an overkill for a small project, but it becomes worth the investment when your projects grow in size.

Answer 4

Rather than debug, it's easier to just write. Give this a go:

#!/bin/bash

test -n "$1" || { echo "error: insufficient input, usage :${0##*/} filename.c (cpp)"; exit 1; }

for source in "$@"; do

    ext="${source##*\.}"  # file extension
    fname="${source##*/}" 
    fname="${fname%\.*}"  # base filename (no extension)

    if test "$ext" == "c" ; then

        gcc -ggdb `pkg-config --cflags opencv` \
        -o "$fname" "$source" \
        `pkg-config --libs opencv`

    elif test "$ext" == "cpp" ; then

        g++ -ggdb `pkg-config --cflags opencv` \
        -o "$fname" "$source" \
        `pkg-config --libs opencv`

    else
        echo "Please compile only .c or .cpp files"

    fi

done

exit 0