问题
This is a bash weirdness that's been bugging me.
I'm on OSX.
I've installed the android SDK, and as a result the adb tool is located in a folder in my home directory. That folder appears in my path as reported by env as ~/Development/android_sdk_latest/platform-tools.
adb itself runs just fine, but when I do which adb the result is empty. If I do command -v adb, the result is the full path, as expected: /Users/me/Development/android_sdk_latest/platform-tools/adb
adb does not appear in my aliases.
What subtlety of bash paths or which am I in the dark on?
回答1:
You've run into a subtle incompatibility between /bin/bash and the which command.
On my system (Linux Mint), the which command is actually a shell script, not a built-in command, and its first line is #! /bin/sh. That means that it uses /bin/sh's handling of the $PATH variable.
This can vary depending on how /bin/sh is set up (it's sometimes a symlink to /bin/bash), but a little experimentation shows that bash handles a literal ~ character in $PATH as if it were the full path to your home directory, but /bin/sh does not. Since you have
~/Development/android_sdk_latest/platform-tools
as one of the elements of your $PATH, bash (your interactive shell) can find the adb command, but sh (the shell used by which) cannot.
On some systems, apparently including your OSX system, which is a binary executable. Again, since it's not a bash script, it's not going to match bash's treatment of $PATH.
I recommend making two changes.
First, don't put a literal ~ in your $PATH. For example, to append the platform-tools directory to your $PATH, rather than this:
export PATH="$PATH:~/Development/android_sdk_latest/platform-tools" # BAD!
do this:
export PATH="$PATH:$HOME/Development/android_sdk_latest/platform-tools"
The $HOME will expand to the path to your home directory (when you run the export command, not when you use $PATH later). ~ is not expanded within double-quoted strings.
Second, rather than using the which command, use the type command that's built into bash. type will follow the rules of your current shell rather than those of /bin/sh, and it will be able to report shell functions and aliases that which is unable to see. It has several useful command-line options; type help type at a bash prompt for details.
The bash shell's treatement of ~ characters in $PATH is documented in the bash manual's section on Tilde Expansion.
来源：https://stackoverflow.com/questions/37579921/bash-which-adb-returns-nothing-but-command-v-adb-returns-what-id-expect