cope with spaces in an environment variable

[Masahiro Yamada]

Hi.

I'd like to know the proper handling of an environment variable
when the value may contain spaces (with quoting).

Here is my question.

You have the environment variable 'CC', which contains a compiler path.

For example, how to write a shell script to
compile a C file with ${CC}?


Here are two prerequisites:

[1] The compiler installation path may contain spaces.
For example, if the compiler is located in '/tmp/a b/',

 export CC="'/tmp/a b/gcc'"

[2] The 'CC' may not be a single word.
    If ccache is used, it can be two words.

  export CC="ccache gcc"



If it were Makefile, the code would be very simple.

  all:
           $(CC) helloworld.c



If you try to do something equivalent in a shell script,
it looks more complex.


Ans1)

  #!/bin/sh
  "${CC}" helloworld.c


This does not work with [2].

  $ export CC="ccache gcc"
  $ ./build-helloworld.sh
  ./build-helloworld.sh: 2: ccache gcc: not found


Ans2)

  #!/bin/sh
  ${CC} helloworld.c

This works with [2], but not [1].

  $ export CC="'/tmp/a b/gcc'"
  $ ./build-helloworld.sh
  ./build-helloworld.sh: 2: '/tmp/a: not found


Ans3)

  #!/bin/sh
  eval "${CC} helloworld.c"

This works with [1], [2], and the combination of them.

  $ mkdir -p '/tmp/a b'
  $ ln -s /usr/bin/gcc '/tmp/a b/gcc'
  $ export CC="ccache '/tmp/a b/gcc'"
  $ ./build-helloworld.sh


So, using 'eval' seems to work for me, but
it is somewhat tedious to repeat 'eval' in each line
that uses ${CC}.

Is this a proper way, or is there a better way?


-- 
Best Regards
Masahiro Yamada