CODEWITHSUNDEEP
shell
Praveen
Praveen

Reputation: 61

What is this line of shell script doing

This question may be pretty simple, but i dont find exact answers ..

in shell script i have a line like this,

export CFLAGS=" -w -Iinc/ -Isrc/"

I dont know what is that -w and -I options doing here??

All i know is this line includes the directories inc and src

Any help would be great

Upvotes: 0

Views: 162

Answers (3)

Jens
Jens

Reputation: 72639

CFLAGS is the name of an environment variable. It gets set to the value -w -Iinc/ -Isrc/ (the initial space is useless, and so are the slashes, btw).

The mechanism how this affects compilation with a C compiler is through the make program. The make utility by default uses this rule to compile a C program to an object file:

.c.o:
    $(CC) $(CFLAGS) -c $<

and imports the make variable $(CFLAGS) from the environment variable $CFLAGS (they are distinct; don't confuse 'em).

You can read all about make variables, make rules and their default values on http://pubs.opengroup.org/onlinepubs/9699919799/utilities/make.html

For enlightenment try this: create an empty Makefile, place the familiar helloworld.c in the same directory and type make helloworld. What happens? Why? If you understand this, you have made a giant leap towards becoming a make guru :-)

Upvotes: 0

Quentin
Quentin

Reputation: 943569

This just sets an environment variable. I'm guessing that it gets used to set flags for GCC.

From man gcc:

   -I dir
       Add the directory dir to the list of directories to be searched for
       header files.  Directories named by -I are searched before the
       standard system include directories.  If the directory dir is a
       standard system include directory, the option is ignored to ensure
       that the default search order for system directories and the
       special treatment of system headers are not defeated .

   -w  Suppress all warnings, including those which GNU CPP issues by
       default.

Upvotes: 2

Michael Petrotta
Michael Petrotta

Reputation: 60902

They're arguments to your compiler. If gcc, then:

  • -w: Inhibit all warning messages.
  • -I: Add the directory dir to the list of directories to be searched for header files. Directories named by '-I' are searched before the standard system include directories. If the directory dir is a standard system include directory, the option is ignored to ensure that the default search order for system directories and the special treatment of system headers are not defeated (see System Headers).

Upvotes: 0

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