Bash: How to feed a command with the multiple results generated by one subcommand

Question

Hi,

I want to process each source code file after it has been preprocessed:

myprocess `gcc -E file1.c`  
myprocess `gcc -E file2.c`  
...  
myprocess `gcc -E fileN.c`

This gets tedious so how do I make this a single command?
That is, something along the line:

myprocess SOMETHINGMAGIC(gcc -E file*.c)

Thanks in advance!

Answer 1

You mean like

   for i in file*.c ; do
        myprocess `gcc -E $i`
    done

Answer 2

If this is part of an ongoing processes (as opposed to a one time thing), use make, it is good at automating work pipelines.

In particular use suffix rules with traditional make or gmake style implicit rules.

Here is an outline for a suffix rule implementation:

.c.cpre:
         $(CC) -E $(CPPFLAGS) -o $@ $<
.cpre.cmy:
         $(MY_PROCESS) $<
         # Or whatever syntax you support..
         #
         # You could 
         # $(RM) $<
         # here, but I don't recommend it
.cmy.o:
         $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@ $<
         # $(RM) $<

Answer 3

Perhaps this is what you're looking for?:

for i in file*.c ; do 
    echo "Header for myprocess: $i" 
    gcc -E $i 2>&1 
done | myprocess

2>&1 assumes you want to grab stderr, too
echo ... gives myprocess a starting point for each compilation

Answer 4

How about:

myprocess {$(gcc -E file1.c),$(gcc -E file2.c),$(gcc -E file3.c)}

Or if you pipe it:

{$(gcc -E file1.c),$(gcc -E file2.c),$(gcc -E file3.c)} | myprocess

It's been a while since I've used bash, so, please, point out my mistakes!

Answer 5

No magic nedded, just

my_process $(gcc -E *.c)

Note that I used the $(command) form because backticks are deprecated.

As an aside: are you sure you want to do that? You are putting the whole output of gcc -E as command line parameters of my_process. Not sure this is what you want. Maybe you want to use a simple pipe

gcc -E file.c | my_process

so that the output of gcc becomes the input of my_process.

In the latter case something like

for c_file in *.c ; do
    gcc -E $c_file | myprocess > ${c_file}.processed
done

would do the trick.

Answer 6

I think Paul's simple loop and dmckee's Makefile solution suit my needs best! Thanks for all your suggestions!

Answer 7

ls file*.c | xargs --replace myprocess $(gcc -E {})