3.7 Build-Script Problems: The cd and set commands

Each build-script line is executed in a separate shell and each build-script line starts in omake's current directory. This causes special problems for some commands. For example, suppose you want to change directory to subdir and run omake recursively. If you use this line

recursion :
chdir subdir
omake $(MFLAGS)

omake $(MFLAGS) is executed from the current directory.

Similarly, setting environment variables does not work as expected because the environment variable is set in one shell, the shell exits back to omake, and the next command is executed in a new shell that doesn't have the variable set. For example, this line

does not echo dgk.

NOTE: In NMAKE emulation mode, omake handles internally any commands that start by setting an environment variable, rather than calling the shell.

Both of these problems can be avoided by using a multiple-command build-script line.

Using Multiple-Command Build-Script Lines

The syntax for executing more than one command in the same shell is

( command [ & command ] ... )

The build-script line is enclosed in parentheses, and the commands are separated by a semicolon (;). (Use \; to specify a literal semicolon). In terms of implementation, omake writes each command to a batch file and uses the shell program named by the .SHELL directive to execute the batch file.

The recursion examples now become

recursion :
( chdir subdir & omake $(MFLAGS) )

Simultaneous support of all operating systems is possible with a conditional macro definition such as this:

%if $(OS) == NT
; = & $; is "&"
%else
; = ; $; is ";"
%endif

The multiple-command build-script line is now written as

After the macros are expanded, the build-script line becomes

Using Directives: %chdir and %setenv

Rather than use a multiple-command build script to work around the change-directory problem, you can use a directive. The %chdir directory directive causes omake to change to directory, where it stays until the next %chdir directive or until omake exits. The recursion example becomes

Likewise, to work around the environment-variable problem you can use a directive. The %setenv name val directive sets environment variable NAME to the value val. Like %chdir, %setenv has effect until the next %setenv or until omake exits. The setenv example becomes

For more information and recommendations on using the %setenv directive, see the %setenv entry in Table 14 here