Makefile Notes

Notes on using GNU Makefiles: hints, tips & tricks, and peculiarities.

Whitespace

• Variable names
All characters are valid except for the colon (:), pound sign (#), and equals sign (=). Leading and trailing whitespace is ignored. However, intermediate whitespace in a variable name is allowed when using the define directive or the loop variable of the foreach directive. For example:

  define MY VAR
  abcd,123
  endef
  ...
  all: ; echo $(MY VAR)

• Variable assignments

  <var>  = <value>
  <var> := <value>
  <var> ?= <value>

Whitespace between the equal sign ("=" or ":=") and <value> is ignored. Whitespace trailing <value> is not ignored.

• Functions general

Whitespace between the function name and the first parameter is ignored.

• addsuffix suffix, names...

Leading or trailing whitespace around names is ignored as is leading whitespace before suffix. However, trailing whitespace after suffix is reduced to one space after the entire expansion.

• foreach var, list, commands

Words in list are stripped from leading and trailing whitespace when they are assigned to var.

• subst from,to,text

All whitespace counts, except between subst and <from>.

• sort list

Removes leading, trailing, and intermediate whitespace.

• findstring find,in

Whitespace following find up until the comma is part of the search string. This means words in in have to be separated by this same amount of trailing whitespace else it won't match.

• basename names...

Removes leading, trailing, and intermediate whitespace.

• dir names...

Removes leading, trailing, and intermediate whitespace.

• notdir names...

Removes leading, trailing, and intermediate whitespace.

• if condition,then-part[,else-part]

Leading and trailing whitespace around condition is removed before expansion.