Shell 测试以查看二进制文件是否在您的路径中
在 csh、tcsh、bash、perl（等）中，您可以进行同等测试（不一定使用相同的语法）：
test -e PATH; # Does PATH exist
test -f PATH; # Is PATH a file
test -d PATH; # is PATh a directory
...
是否存在类似的构造来检查二进制文件是否在您的路径中？ （也许是否存在别名，甚至是内置的）
显然，这可以通过以下形式来完成：
#!/usr/bin/env bash
C=COMMAND;
test $(which $C) -o $(alias $C) && "$C exists"
或在其他 shell/脚本语言中类似的东西。
问题不在于是否可以测试程序、命令等是否存在。问题在于是否存在内置测试。
In csh, tcsh, bash, perl (etc) you can do tests on par with (not necessarily with the same syntax):
test -e PATH; # Does PATH exist
test -f PATH; # Is PATH a file
test -d PATH; # is PATh a directory
...
Does a similar construct exist for checking whether a binary is in your path? (and perhaps whether an alias, or even a built-in exist)
Obviously this can be done with something of the form:
#!/usr/bin/env bash
C=COMMAND;
test $(which $C) -o $(alias $C) && "$C exists"
or something similar in other shells/script languages.
The question isn't whether it's possible to test for the existence of a program, command, etc. The question is whether a built-in test exists or not.
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从技术上讲，如果您只是在当前
PATH中查找内容，那么唯一真正的解决方案是第二个代码块的第一部分：which是当前PATH中唯一真正符合您的实际要求的，因为whereis将在路径之外搜索：和
alias当然与实际的可执行文件无关，而是 shell 环境中的别名命令所以，实际上，您已经有了正确的方法，只是要小心，您知道
whereis可能不会对测试链有帮助。Technically if you're just looking for stuff in the current
PATHthen the only real solution is the first portion of your second code block:whichis the only one that really fits your actual requirement of in the currentPATHaswhereiswill search outside the path:and
aliasof course has nothing to do with actual executables, but rather aliased commands within your shell environmentSo, really, you've got the right approach already, just be careful that you know that
whereismay not be a helpful addition to that chain of tests.或者只是：
Or just:
另一种解决方案是
“Executable”是所需应用程序的名称。
例如：
返回
An alternative solution is
Where Executable is the name of the wanted application.
For example:
returns