In the Makefile each action line is a separate invocation of a shell child process and any shell variables or current working directory changes are independent of each other.

The following table shows how to compress the various Bourne shell statements onto a single logical line. However, it's a good idea to break up the statements with white-space formatting on to separate lines. This can be done by escaping the new-line.

Other hints:

• Set the macro SHELL=/bin/sh to make sure which shell will be invoked. (If you pick some other shell there's no guarantee that the implementation of make will honor it.)
• Use $$variable to reference a shell variable (such as in the for loop). The ``$$'' tells make to not do any macro expansion.
• Use test instead of [ and ], since errors occur when there is inadequate spacing given for the brackets.
• Either quote or rely on string catenation for comparisons, e.g.
  test "$$x" = "abc"     or
  test x$$x = xabc
  test doesn't handle empty arguments too well!
• Become familiar with expr for doing simple math operations and parsing.
• Likewise with basename and dirname for parsing out parts of the file name and path.
• Understand when to use quotes (") or apostrophes (').

Bourne Shell conditional and looping statements

Expanded	Condensed
if com1 then com2 fi	if com1 ; then com2 ; fi
if com1 then com2 else com3 fi	if com1 ; then com2 ; else com3 ; fi
if com1 then com2 elif com3 then com4 else com5 fi	if com1 ; then com2 ; elif com3 ; \ then com4 ; else com5 ; fi
case value in pattern1) com1 ;; pattern2) com2 ;; pattern3) com3 ;; esac	case value in pattern1) com1 ;; \ pattern2) com2 ;; \ pattern3) com3 ;; esac
for variable in list do command done	for variable in list; do command ; done
while com1 do com2 done	while com1 ; do com2 ; done
until com1 do com2 done	until com1 ; do com2 ; done