Editing SCons (section)

=== Command-line options ===

{|class="wikitable" align="center" cellspacing="0" border="1"
|-
! colspan="2" style="background:#ffdead;"|Command-line options
|-
| '''Name''' || '''Meaning'''
|-
| TIMER || Whether to time execution
|-
| CHECKPAR || Whether to check parameters
|-
| ENVIRON || Additional environment settings
|-
| CLUSTER || Nodes available on a cluster
|-
| MPIRUN || mpirun command
|}

Running the example above with <tt>TIMER=y</tt> produces
<syntaxhighlight lang="bash">
bash$ scons -Q TIMER=y
/usr/bin/time < wind.rsf /RSF/bin/sfmutter v0=0.32 half=n > mute.rsf
0.09user 0.03system 0:00.13elapsed 94%CPU (0avgtext+0avgdata 383744maxresident)k
0inputs+0outputs (1513major+0minor)pagefaults 0swaps
/usr/bin/time < mute.rsf /RSF/bin/sfpow pow1=2 | /RSF/bin/sfgrey > mute.vpl
0.10user 0.00system 0:00.18elapsed 59%CPU (0avgtext+0avgdata 384256maxresident)k
0inputs+0outputs (1515major+0minor)pagefaults 0swaps
/usr/bin/time /RSF/bin/vppen yscale=2 vpstyle=n gridnum=2,1 wind.vpl mute.vpl > Fig/denmark.vpl
0.06user 0.03system 0:00.06elapsed 135%CPU (0avgtext+0avgdata 444416maxresident)k
0inputs+0outputs (1739major+0minor)pagefaults 0swaps
</syntaxhighlight>
In other words, every shell command is preceded by the Unix [http://en.wikipedia.org/wiki/Time_%28Unix%29 time] utility to measure the CPU time of the process.

Running the example above with <tt>CHECKPAR=y</tt>, we will not see any difference. Suppose, however, that we made a typo in specifying one of the parameters, for example, by using <tt>v1=</tt> instead of <tt>v0=</tt> in the arguments to <tt>sfmutter</tt>.
<syntaxhighlight lang="bash">
bash$ sed -i s/v0=0.31/v1=0.31/ SConstruct
bash$ scons -Q CHECKPAR=y
No parameter "v1" in sfmutter
Failed on "mutter v1=0.31 half=n"
</syntaxhighlight>
The parameter error gets detected by <tt>scons</tt> before anything is executed.