(make.info.gz) Splitting Lines

(make.info.gz) Variables in Commands
 
 5.1.1 Splitting Command Lines
 -----------------------------
 
 One of the few ways in which `make' does interpret command lines is
 checking for a backslash just before the newline.  As in normal
 makefile syntax, a single command can be split into multiple lines in
 the makefile by placing a backslash before each newline.  A sequence of
 lines like this is considered a single command, 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, backslash-newline pairs are _not_ removed from the command.
 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 a tab, then that tab (and only that tab) is
 removed.  Whitespace is never added to the command.
 
    For example, 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 run one shell with a command script 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 command.  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 (
 Target-specific Variable Values Target-specific.) to obtain a tighter
 correspondence between the variable and the command that uses it.
Info Catalog
(make.info.gz) Command Syntax
(make.info.gz) Variables in Commands
automatically generated byinfo2html