[SOLVED] 'configure_file' incorrectly expands a variable

Issue

I have the following codes in mylib.pc.in, and want to use the CMake command configure_file(mylib.pc.in mylib.pc) to generate a correct mylib.pc file which is expanded from mylib.pc.in; but this doesn't work.

prefix=$ENV{HOME}/xcompiled-root/
exe_prefix=${prefix}
libdir=${prefix}/lib
includedir=${prefix}/include

Name: @PROJECT_NAME@
Description: @PROJECT_DESCRIPTION@
Version: @PROJECT_VERSION@

Requires:
Libs: -L@{libdir} -lpthread -lrt -ldl  -lm
Cflags: -I@{includedir}

I just want the mylib.pc be something like this:

prefix=/home/myusr/xcompiled-root/
exe_prefix=/home/myusr/xcompiled-root/
libdir=/home/myusr/xcompiled-root/lib
includedir=/home/myusr/xcompiled-root/include
...

but I get this:

prefix=/home/myusr/xcompiled-root/
exe_prefix=
libdir=/lib
includedir=/include
...

what should I do?!

Solution

Construction ${prefix} is a variable reference both in CMake scripting and in .pc file scripting. So you need to choose at which stage you want to expand this reference:

1. If you want CMake to expand this reference, you need to have a CMake variable named prefix when you use configure_file:

   # File: CMakeLists.txt
   set(prefix "$ENV{HOME}/xcompiled-root/")
   configure_file(mylib.pc.in mylib.pc)
   

   Note, that with such setting you no longer need to define prefix variable in .pc file:

   # File: mylib.pc.in
   exe_prefix=${prefix}
   libdir=${prefix}/lib
   includedir=${prefix}/include
   

   Resulted mylib.pc file will be:

   exe_prefix=/home/myusr/xcompiled-root/
   libdir=/home/myusr/xcompiled-root/lib
   includedir=/home/myusr/xcompiled-root/include
   

2. If you want to expand variable reference ${prefix} only when pkg-config is called, you need to prevent CMake to expand this reference. E.g. you may insert ${} construction, which expanded by CMake to nothing, between $ and { characters:

   # File: mylib.pc.in
   prefix=$ENV{HOME}/xcompiled-root/
   exe_prefix=$${}{prefix}
   libdir=$${}{prefix}/lib
   includedir=$${}{prefix}/include
   

   Then, with common configure_file

   # File: CMakeLists.txt
   configure_file(mylib.pc.in mylib.pc)
   

   you will have following mylib.pc file:

   prefix=/home/myusr/xcompiled-root/
   exe_prefix=${prefix}
   libdir=${prefix}/lib
   includedir=${prefix}/include
   

   When this file will be processed by pkg-config, ${prefix} will be expanded (internally) to /home/myusr/xcompiled-root/.

3. If you do not want to bother about escaping ${} construction, use @ONLY option for configure_file. With that option CMake only expands @VAR@ but leaves ${var} unchanged:

   # File: CMakeLists.txt
   # Construction @VAR@ doesn't support reference to environment variable.
   # So prepare pure CMake variable which contains $ENV{HOME}.
   set(user_home "$ENV{HOME}")
   configure_file(mylib.pc.in mylib.pc @ONLY)
   

   With @ONLY option you may simply use $ in the .in:

   prefix=@user_home@/xcompiled-root/
   exe_prefix=${prefix}
   libdir=${prefix}/lib
   includedir=${prefix}/include
   
   Name: @PROJECT_NAME@
   Description: @PROJECT_DESCRIPTION@
   Version: @PROJECT_VERSION@
   
   Requires:
   Libs: -L@{libdir} -lpthread -lrt -ldl  -lm
   Cflags: -I@{includedir}
   

   Note, that CMake leaves unchanged @{var} construction too. This is because { character is not valid for a variable's name in CMake.

Answered By - Tsyvarev

Answer Checked By - Marie Seifert (WPSolving Admin)