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3.4 Staying below the command line length limit

Traditionally, most unix-like systems have a length limitation for the command line arguments and environment contents when creating new processes (see for example for an overview on this issue), which of course also applies to commands spawned by make. POSIX requires this limit to be at least 4096 bytes, and most modern systems have quite high limits (or are unlimited).

In order to create portable Makefiles that do not trip over these limits, it is necessary to keep the length of file lists bounded. Unfortunately, it is not possible to do so fully transparently within Automake, so your help may be needed. Typically, you can split long file lists manually and use different installation directory names for each list. For example,

data_DATA = file1 … fileN fileN+1 … file2N

may also be written as

data_DATA = file1 … fileN
data2dir = $(datadir)
data2_DATA = fileN+1 … file2N

and will cause Automake to treat the two lists separately during make install. See The Two Parts of Install for choosing directory names that will keep the ordering of the two parts of installation Note that make dist may still only work on a host with a higher length limit in this example.

Automake itself employs a couple of strategies to avoid long command lines. For example, when ‘${srcdir}/’ is prepended to file names, as can happen with above $(data_DATA) lists, it limits the amount of arguments passed to external commands.

Unfortunately, some system’s make commands may prepend VPATH prefixes like ‘${srcdir}/’ to file names from the source tree automatically (see Automatic Rule Rewriting in The Autoconf Manual). In this case, the user may have to switch to use GNU Make, or refrain from using VPATH builds, in order to stay below the length limit.

For libraries and programs built from many sources, convenience archives may be used as intermediates in order to limit the object list length (see Libtool Convenience Libraries).

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