在前面一篇文章里shell如何模块化和复用——shell深入学习，我介绍了一种shell的模块化做法，但是在实际的代码中我估计很少人会这么处理，相反，有另一种组织方式（或者称为模块化方式吧）在一些开源代码中可以见到，感觉更符合shell的语言特性。
由于shell的source语句（. 语句）本质上是在当前的shell进程中执行script脚本文件，所以如果这个脚本文件中不是单纯的定义子函数被导入上调用（也就是我们所谓的子模块或者库），那么他就类似于VM中的一个子control，仅仅是为了避免重复代码，而且往往需要导入多次（因为导入就是为了执行该子shell）。而对于作为子模块的子shell文件，我们其实是希望他只被导入一次的（因为我们是要导入他定义的子函数）。这种方式其实在很多开源软件中很常见，因为本身shell其实就不是一个模块话的语言，虽然可以通过某些机制让他支持，但是成本高而且没有太大必要。相比之下，后者具有更大的可操作性。比如最简单，而且也是最的常见的做法，就是将一个函数的函数体抽出来，放在一个单独的shell脚本中，如果调用该脚本的话，那么就提交将参数设置好，然后source一下该脚本，这样就相当于调用了该子函数（有个缺点就是参数和返回值是通过约定好的变量进行）。
举个具体的实际例子，nginx的configure脚本就是这么处理的：在总入口configure shell脚本中，大量的调用（导入）在auto目录下的子shell函数（脚本）：
forrest@ubuntu:~/Install/nginx-1.0.12$ tree auto/
auto/
├── cc
│ ├── acc
│ ├── bcc
│ ├── ccc
│ ├── conf
│ ├── gcc
│ ├── icc
│ ├── msvc
│ ├── name
│ ├── owc
│ └── sunc
├── define
├── endianess
├── feature
├── have
├── have_headers
├── headers
├── include
├── init
├── install
├── lib
│ ├── conf
│ ├── geoip
│ │ └── conf
│ ├── google-perftools
│ │ └── conf
│ ├── libatomic
│ │ ├── conf
│ │ └── make
│ ├── libgd
│ │ └── conf
│ ├── libxslt
│ │ └── conf
│ ├── make
│ ├── md5
│ │ ├── conf
│ │ ├── make
│ │ ├── makefile.bcc
│ │ ├── makefile.msvc
│ │ └── makefile.owc
│ ├── openssl
│ │ ├── conf
│ │ ├── make
│ │ ├── makefile.bcc
│ │ └── makefile.msvc
│ ├── pcre
│ │ ├── conf
│ │ ├── make
│ │ ├── makefile.bcc
│ │ ├── makefile.msvc
│ │ └── makefile.owc
│ ├── perl
│ │ ├── conf
│ │ └── make
│ ├── sha1
│ │ ├── conf
│ │ ├── make
│ │ ├── makefile.bcc
│ │ ├── makefile.msvc
│ │ └── makefile.owc
│ ├── test
│ └── zlib
│ ├── conf
│ ├── make
│ ├── makefile.bcc
│ ├── makefile.msvc
│ ├── makefile.owc
│ └── patch.zlib.h
├── make
├── modules
├── nohave
├── options
├── os
│ ├── conf
│ ├── darwin
│ ├── freebsd
│ ├── linux
│ ├── solaris
│ └── win32
├── sources
├── stubs
├── summary
├── types
│ ├── sizeof
│ ├── typedef
│ ├── uintptr_t
│ └── value
└── unix
如其中的. auto/feature在多个shell中都被导入过（而且有些还不只一次，这取决于调用的次数）： 有95个地方调用到了：
forrest@ubuntu:~/study/nginx-1.0.12$ find . | xargs grep -Hn '. auto/feature'
./auto/unix:42:. auto/feature
./auto/unix:61:. auto/feature
./auto/unix:78: . auto/feature
./auto/unix:95: . auto/feature
./auto/unix:125: . auto/feature
./auto/unix:157:. auto/feature
./auto/unix:168: . auto/feature
./auto/unix:183:. auto/feature
./auto/unix:193:. auto/feature
./auto/unix:203:. auto/feature
./auto/unix:217:. auto/feature
./auto/unix:228:. auto/feature
./auto/unix:241:. auto/feature
./auto/unix:253:. auto/feature
./auto/unix:263:. auto/feature
./auto/unix:270: . auto/feature
./auto/unix:285:. auto/feature
./auto/unix:292: . auto/feature
./auto/unix:307:. auto/feature
./auto/unix:317:. auto/feature
./auto/unix:329:. auto/feature
./auto/unix:339:. auto/feature
./auto/unix:352: . auto/feature
./auto/unix:371: . auto/feature
./auto/unix:463: . auto/feature
./auto/unix:474:. auto/feature
./auto/unix:484:. auto/feature
./auto/unix:494:. auto/feature
./auto/unix:505:. auto/feature
./auto/unix:519: . auto/feature
./auto/unix:547: . auto/feature
./auto/unix:558:. auto/feature
./auto/unix:568:. auto/feature
./auto/unix:578:. auto/feature
./auto/unix:591:. auto/feature
./auto/unix:606:. auto/feature
./auto/unix:620:. auto/feature
./auto/unix:632:. auto/feature
./auto/unix:640: . auto/feature
./auto/unix:653: . auto/feature
./auto/unix:668:. auto/feature
./auto/unix:679:. auto/feature
./auto/unix:689:. auto/feature
./auto/unix:699:. auto/feature
./auto/unix:709:. auto/feature
./auto/lib/openssl/conf:52: . auto/feature
./auto/lib/geoip/conf:13: . auto/feature
./auto/lib/geoip/conf:28: . auto/feature
./auto/lib/geoip/conf:45: . auto/feature
./auto/lib/geoip/conf:62: . auto/feature
./auto/lib/libgd/conf:13: . auto/feature
./auto/lib/libgd/conf:29: . auto/feature
./auto/lib/libgd/conf:46: . auto/feature
./auto/lib/libgd/conf:63: . auto/feature
./auto/lib/sha1/conf:52: . auto/feature
./auto/lib/sha1/conf:63: . auto/feature
./auto/lib/md5/conf:62: . auto/feature
./auto/lib/md5/conf:72: . auto/feature
./auto/lib/md5/conf:86: . auto/feature
./auto/lib/google-perftools/conf:13: . auto/feature
./auto/lib/google-perftools/conf:28: . auto/feature
./auto/lib/libatomic/conf:30: . auto/feature
./auto/lib/pcre/conf:98: . auto/feature
./auto/lib/pcre/conf:113: . auto/feature
./auto/lib/pcre/conf:124: . auto/feature
./auto/lib/pcre/conf:140: . auto/feature
./auto/lib/pcre/conf:156: . auto/feature
./auto/lib/zlib/conf:54: . auto/feature
./auto/lib/libxslt/conf:22: . auto/feature
./auto/lib/libxslt/conf:38: . auto/feature
./auto/lib/libxslt/conf:55: . auto/feature
./auto/lib/libxslt/conf:72: . auto/feature
./auto/lib/libxslt/conf:101: . auto/feature
./auto/lib/libxslt/conf:116: . auto/feature
./auto/lib/libxslt/conf:133: . auto/feature
./auto/lib/libxslt/conf:150: . auto/feature
./auto/os/linux:61:. auto/feature
./auto/os/linux:85:. auto/feature
./auto/os/linux:106:. auto/feature
./auto/os/linux:120:. auto/feature
./auto/os/linux:133:. auto/feature
./auto/os/linux:146:. auto/feature
./auto/os/solaris:39:. auto/feature
./auto/os/solaris:55:. auto/feature
./auto/os/darwin:54:. auto/feature
./auto/os/darwin:81:. auto/feature
./auto/os/darwin:100:. auto/feature
./auto/os/darwin:116:. auto/feature
./auto/cc/gcc:30:. auto/feature
./auto/cc/name:15: . auto/feature
./auto/cc/conf:120: . auto/feature
./auto/cc/conf:144: . auto/feature
./auto/cc/conf:160: . auto/feature
./auto/cc/conf:174: . auto/feature
./auto/cc/conf:184:# . auto/feature
forrest@ubuntu:~/study/nginx-1.0.12$ find . | xargs grep '. auto/feature' | wc -l
95
有如下17个文件使用到了：
forrest@ubuntu:~/study/nginx-1.0.12$ find . | xargs grep -l '. auto/feature'
./auto/unix
./auto/lib/openssl/conf
./auto/lib/geoip/conf
./auto/lib/libgd/conf
./auto/lib/sha1/conf
./auto/lib/md5/conf
./auto/lib/google-perftools/conf
./auto/lib/libatomic/conf
./auto/lib/pcre/conf
./auto/lib/zlib/conf
./auto/lib/libxslt/conf
./auto/os/linux
./auto/os/solaris
./auto/os/darwin
./auto/cc/gcc
./auto/cc/name
./auto/cc/conf
forrest@ubuntu:~/study/nginx-1.0.12$ find . | xargs grep -l '. auto/feature' | wc -l
17
那么auto/feature里面到底定义了什么了：
forrest@ubuntu:~/Install/nginx-1.0.12$ cat auto/feature
# Copyright (C) Igor Sysoev
# Copyright (C) Nginx, Inc.
echo $ngx_n "checking for $ngx_feature ...$ngx_c"
cat << END >> $NGX_AUTOCONF_ERR
----------------------------------------
checking for $ngx_feature
END
ngx_found=no
if test -n "$ngx_feature_name"; then
ngx_have_feature=`echo $ngx_feature_name \
| tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ`
fi
if test -n "$ngx_feature_path"; then
for ngx_temp in $ngx_feature_path; do
ngx_feature_inc_path="$ngx_feature_inc_path -I $ngx_temp"
done
fi
cat << END > $NGX_AUTOTEST.c
#include <sys/types.h>
$NGX_INCLUDE_UNISTD_H
$ngx_feature_incs
int main() {
$ngx_feature_test;
return 0;
}
END
ngx_test="$CC $CC_TEST_FLAGS $CC_AUX_FLAGS $ngx_feature_inc_path \
-o $NGX_AUTOTEST $NGX_AUTOTEST.c $NGX_TEST_LD_OPT $ngx_feature_libs"
ngx_feature_inc_path=
eval "/bin/sh -c \"$ngx_test\" >> $NGX_AUTOCONF_ERR 2>&1"
if [ -x $NGX_AUTOTEST ]; then
case "$ngx_feature_run" in
yes)
# /bin/sh is used to intercept "Killed" or "Abort trap" messages
if /bin/sh -c $NGX_AUTOTEST >> $NGX_AUTOCONF_ERR 2>&1; then
echo " found"
ngx_found=yes
if test -n "$ngx_feature_name"; then
have=$ngx_have_feature . auto/have
fi
else
echo " found but is not working"
fi
;;
value)
# /bin/sh is used to intercept "Killed" or "Abort trap" messages
if /bin/sh -c $NGX_AUTOTEST >> $NGX_AUTOCONF_ERR 2>&1; then
echo " found"
ngx_found=yes
cat << END >> $NGX_AUTO_CONFIG_H
#ifndef $ngx_feature_name
#define $ngx_feature_name `$NGX_AUTOTEST`
#endif
END
else
echo " found but is not working"
fi
;;
bug)
# /bin/sh is used to intercept "Killed" or "Abort trap" messages
if /bin/sh -c $NGX_AUTOTEST >> $NGX_AUTOCONF_ERR 2>&1; then
echo " not found"
else
echo " found"
ngx_found=yes
if test -n "$ngx_feature_name"; then
have=$ngx_have_feature . auto/have
fi
fi
;;
*)
echo " found"
ngx_found=yes
if test -n "$ngx_feature_name"; then
have=$ngx_have_feature . auto/have
fi
;;
esac
else
echo " not found"
echo "----------" >> $NGX_AUTOCONF_ERR
cat $NGX_AUTOTEST.c >> $NGX_AUTOCONF_ERR
echo "----------" >> $NGX_AUTOCONF_ERR
echo $ngx_test >> $NGX_AUTOCONF_ERR
echo "----------" >> $NGX_AUTOCONF_ERR
fi
rm $NGX_AUTOTEST*
我们看到，它其实是根据传递过来的变量，生成一个测试$NGX_AUTOTEST.c文件，然后调用CC编译器编译看是否通过（设置ngx_found变量），如果设置了$ngx_feature_run为yes，那么还会执行编译后的测试文件。如果通过说明当前操作系统支持这个feature，否则就是不支持。
同样，auto/have也被调用（导入）了多次。
—EOF—
