bash 如何在 Makefile 中使用 shell 命令
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How to use shell commands in Makefile
提问by Adam Matan
I'm trying to use the result of lsin other commands (e.g. echo, rsync):
我正在尝试使用ls其他命令（例如 echo、rsync）中的结果：
all:
<Building, creating some .tgz files - removed for clarity>
FILES = $(shell ls)
echo $(FILES)
But I get:
但我得到：
make
FILES = Makefile file1.tgz file2.tgz file3.tgz
make: FILES: No such file or directory
make: *** [all] Error 1
I've tried using echo $$FILES, echo ${FILES}and echo $(FILES), with no luck.
我试过使用echo $$FILES,echo ${FILES}和echo $(FILES)，但没有运气。
回答by torek
With:
和：
FILES = $(shell ls)
indented underneath alllike that, it's a build command. So this expands $(shell ls), then tries to run the command FILES ....
all像这样在下面缩进，这是一个构建命令。所以这会展开$(shell ls)，然后尝试运行命令FILES ...。
If FILESis supposed to be a makevariable, these variables need to be assigned outside the recipe portion, e.g.:
如果FILES应该是make变量，则需要在配方部分之外分配这些变量，例如：
FILES = $(shell ls)
all:
echo $(FILES)
Of course, that means that FILESwill be set to "output from ls" beforerunning any of the commands that create the .tgz files. (Though as Kaz notesthe variable is re-expanded each time, so eventually it will include the .tgz files; some make variants have FILES := ...to avoid this, for efficiency and/or correctness.1)
当然，这意味着在运行任何创建 .tgz 文件的命令之前，FILES它将被设置为“输出ls” 。（尽管Kaz 指出变量每次都会重新扩展，因此最终它将包含 .tgz 文件；为了效率和/或正确性，一些 make 变体必须避免这种情况。1）FILES := ...
If FILESis supposed to be a shell variable, you can set it but you need to do it in shell-ese, with no spaces, and quoted:
如果FILES应该是一个shell变量，你可以设置它，但你需要在shell-ese中进行，没有空格，并引用：
all:
FILES="$(shell ls)"
However, each line is run by a separate shell, so this variable will not survive to the next line, so you must then use it immediately:
然而，每一行都由一个单独的 shell 运行，所以这个变量不会保留到下一行，所以你必须立即使用它：
FILES="$(shell ls)"; echo $$FILES
This is all a bit silly since the shell will expand *(and other shell glob expressions) for you in the first place, so you can just:
这有点傻，因为 shell 首先会*为您扩展（和其他 shell glob 表达式），所以您可以：
echo *
as your shell command.
作为你的 shell 命令。
Finally, as a general rule (not really applicable to this example): as esperantonotes in comments, using the output from lsis not completely reliable (some details depend on file names and sometimes even the version of ls; some versions of lsattempt to sanitize output in some cases). Thus, as l0b0and idelicnote, if you're using GNU make you can use $(wildcard)and $(subst ...)to accomplish everything inside makeitself (avoiding any "weird characters in file name" issues). (In shscripts, including the recipe portion of makefiles, another method is to use find ... -print0 | xargs -0to avoid tripping over blanks, newlines, control characters, and so on.)
最后，作为一般规则（并非真正适用于本示例）：正如世界语注释中的注释，使用 from 的输出ls并不完全可靠（某些细节取决于文件名，有时甚至取决于 的版本ls；某些版本的ls尝试清理输出在某些情况下）。因此，正如l0b0和理想的注释，如果您使用 GNU make，您可以使用$(wildcard)并$(subst ...)完成其内部的所有内容make（避免任何“文件名中的奇怪字符”问题）。（在sh脚本中，包括 makefile 的配方部分，另一种方法是find ... -print0 | xargs -0用来避免被空格、换行符、控制字符等绊倒。）
1The GNU Make documentation notes further that POSIX make added ::=assignment in 2012. I have not found a quick reference link to a POSIX document for this, nor do I know off-hand which makevariants support ::=assignment, although GNU make does today, with the same meaning as :=, i.e., do the assignment right now with expansion.
1 GNU Make 文档进一步指出 POSIX::=在 2012 年增加了分配。我还没有找到一个指向 POSIX 文档的快速参考链接，我也不知道哪些make变体支持::=赋值，尽管 GNU make 今天做了，与:=，即，现在用扩展做赋值。
Note that VAR := $(shell command args...)can also be spelled VAR != command args...in several makevariants, including all modern GNU and BSD variants as far as I know. These other variants do not have $(shell)so using VAR != command args...is superior in both being shorter andworking in more variants.
请注意，VAR := $(shell command args...)也可以拼写VAR != command args...为多种make变体，包括据我所知的所有现代 GNU 和 BSD 变体。这些其他变体没有，$(shell)因此在更VAR != command args...短和在更多变体中工作方面都具有优势。
回答by Kaz
Also, in addition to torek's answer: one thing that stands out is that you're using a lazily-evaluated macro assignment.
此外，除了 torek 的回答：突出的一件事是您正在使用延迟评估的宏分配。
If you're on GNU Make, use the :=assignment instead of =. This assignment causes the right hand side to be expanded immediately, and stored in the left hand variable.
如果您使用 GNU Make，请使用:=赋值而不是=. 此赋值导致右侧立即展开，并存储在左侧变量中。
FILES := $(shell ...) # expand now; FILES is now the result of $(shell ...)
FILES = $(shell ...) # expand later: FILES holds the syntax $(shell ...)
If you use the =assignment, it means that every single occurrence of $(FILES)will be expanding the $(shell ...)syntax and thus invoking the shell command. This will make your make job run slower, or even have some surprising consequences.
如果您使用=赋值，则意味着每次出现的$(FILES)都将扩展$(shell ...)语法并因此调用 shell 命令。这将使您的 make 作业运行得更慢，甚至会产生一些令人惊讶的后果。
