File: make.info,  Node: Splitting Recipe Lines,  Next: Variables in Recipes,  Prev: Recipe_Syntax.php">Recipe Syntax,  Up: Recipe_Syntax.php">Recipe Syntax

5.1.1 Splitting Recipe Lines
----------------------------

One of the few ways in which 'make' does interpret recipes is checking
for a backslash just before the newline.  As in normal makefile syntax,
a single logical recipe line can be split into multiple physical lines
in the makefile by placing a backslash before each newline.  A sequence
of lines like this is considered a single recipe line, and one instance
of the shell will be invoked to run it.

   However, in contrast to how they are treated in other places in a
makefile (*note Splitting Long Lines: Splitting Lines.),
backslash/newline pairs are _not_ removed from the recipe.  Both the
backslash and the newline characters are preserved and passed to the
shell.  How the backslash/newline is interpreted depends on your shell.
If the first character of the next line after the backslash/newline is
the recipe prefix character (a tab by default; *note Special
Variables::), then that character (and only that character) is removed.
Whitespace is never added to the recipe.

   For example, the recipe for the all target in this makefile:

     all :
             @echo no\
     space
             @echo no\
             space
             @echo one \
             space
             @echo one\
              space

consists of four separate shell commands where the output is:

     nospace
     nospace
     one space
     one space

   As a more complex example, this makefile:

     all : ; @echo 'hello \
             world' ; echo "hello \
         world"

will invoke one shell with a command of:

     echo 'hello \
     world' ; echo "hello \
         world"

which, according to shell quoting rules, will yield the following
output:

     hello \
     world
     hello     world

Notice how the backslash/newline pair was removed inside the string
quoted with double quotes ('"..."'), but not from the string quoted with
single quotes (''...'').  This is the way the default shell ('/bin/sh')
handles backslash/newline pairs.  If you specify a different shell in
your makefiles it may treat them differently.

   Sometimes you want to split a long line inside of single quotes, but
you don't want the backslash/newline to appear in the quoted content.
This is often the case when passing scripts to languages such as Perl,
where extraneous backslashes inside the script can change its meaning or
even be a syntax error.  One simple way of handling this is to place the
quoted string, or even the entire command, into a 'make' variable then
use the variable in the recipe.  In this situation the newline quoting
rules for makefiles will be used, and the backslash/newline will be
removed.  If we rewrite our example above using this method:

     HELLO = 'hello \
     world'

     all : ; @echo $(HELLO)

we will get output like this:

     hello world

   If you like, you can also use target-specific variables (*note
Target-specific Variable Values: Target-specific.) to obtain a tighter
correspondence between the variable and the recipe that uses it.