The shell separates command line parameters by
whitespace, such as the spaces before -expr.
But escaping a space tells the shell not to process
it as such, instead it gets passed to the invoked
program.
So with “\ -expr” on the command line, the shell
passes " -expr" (with a leading space) to 3dcalc,
not “-expr” (without).
Similarly, if there were yet more space after the '',
as in " \ -expr", then the space would not be
attached to “-expr”, but would still be passed to
3dcalc, this time as a separate option.
rick
The
National Institute of Mental Health (NIMH) is part of the National Institutes of
Health (NIH), a component of the U.S. Department of Health and Human
Services.