Develop Reference

Error: ANDROID_HOME is not set and "android" command not in your PATH. You must fulfill at least one of these conditions

I am MAC OS X Yosemite I have done all the export tutorial to set the android_home but non of it working for me

Making sure ANDROID_HOME is exported and adding the SDK tool directories to PATH should be more than enough to get you going.
Using the terminal
# First, we make sure we have a newline at the end of the .bash_profile
echo >> /Users/abdi/.bash_profile
# We set the ANDROID_HOME value in the .bash_profile
echo "export ANDROID_HOME=/Users/abdi/adt/sdk" >> /Users/abdi/.bash_profile
# We alter the PATH value a bit as well
echo "export PATH=${PATH}:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools" >> /Users/abdi/.bash_profile
# We then tell the terminal to update all the things
. /Users/abdi/.bash_profile
Using a GUI (mostly)
You can also open the .bash_profile file in TextEdit using the open -e /Users/abdi/.bash_profile command. If you get some errors about missing files, try running touch /Users/abdi/.bash_profile and retry the open command. In the file that opens, add the following lines at the end.
export ANDROID_HOME=/Users/abdi/adt/sdk
export PATH=${PATH}:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools
Running . /Users/abdi/.bash_profile as in the terminal version after that should get you fully set up.

First need to set the ANDROID_HOME directory
look into your android-sdk-linux(mac) directory and look for 'android' executable file, generally it will exists under 'tools' directory
so edit your .bashrc from home folder
and add this line down there
export ANDROID_HOME=~/android-sdk-linux
PATH=${PATH}:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools
Once done, exit your console and run your command again
You could expect an error saying " Please install Android target "android-19" " if it is not set yet.
you may fix that running "android" command and selecting "Android 4.4.2 API 19" to install.
And afterwards, don't forget to give ample permission to directory where the application resides.

I had the same problem. Luckily it is easily fixable. Just follow the next few steps (Command-line from terminal).
Open the bash_profile file using command line arguments with -
vi ~/.bash_profile
OR
It is possible to open bash_profile in TextEdit and make changes there. Use the following command to do this -
open -a "TextEdit" .bash_profile
Check if ANDROID_HOME has been set in this file. If it has been already set, delete it (probably wrong). Also check if PATH in this file has any reference to tools or platform-tools (of the android sdk). You'd be better off deleting these before you start typing the following commands.
Set ANDROID_HOME correctly using the following command
export ANDROID_HOME=/Users/adarsh/android-sdk-macosx
^this is my command because I installed it in that location. Please replace "adarsh" with your username and "android-sdk-manager" with the name of your android sdk folder that you downloaded. Do not copy-paste this command.
For example, if your username is "John" and you the android sdk folder you downloaded and installed is in "Downloads" and you changed your folder name to "sdk", then your command would be -
export ANDROID_HOME=/Users/John/Downloads/sdk
Set PATH with the following command
export PATH=$ANDROID_HOME/tools:$PATH
Refresh your bash_profile to set all the changes we just made by typing the command
source ~/.bash_profile
You should be good to go now and begin developing with ionic!Hope this helps. Cheers.

One source of this problem comes from sudo. If you're sure you've set $ANDROID_HOME correctly then try the following:
sudo visudo
then add
Defaults env_keep += "ANDROID_HOME"

Make sure the env variable you exported is ANDROID_HOME and not android_home (case sensitive).
After you export, test it by typing
> echo $ANDROID_HOME
The result should point to the dir where you installed the SDK.
Last but not least edit your /etc/paths to add dirs $ANDROID_HOME/platform-tools or /Users/abdi/adt/sdk/platform-tools and $ANDROID_HOME/tools or /Users/abdi/adt/sdk/tools to the list. Save file. You might need to edit this file as admin if need be. Close terminal and then Open new terminal. Then type
> echo $PATH
to check if the path is updated.
And then voila, when you type
> which android
you should see the correct path to the binary returned which in your case is /Users/abdi/adt/sdk/tools/android. you should be all set now.

None of the solutions here solved my problem completely. My Node version was little bit old and ionic was giving a warning to upgrade node. After upgrading Node, I had to delete the project and again create the project, then perform all the steps. Hope this helps somebody.

-bash: android: command not found on Mac OSX

I've been diving into Android development for a while, and now I want to use some project (helpshift) in my app. On the website they have some example apps in which the readme says: Run the following inside the /HelpshiftDemo folder.
android update project -t android-17 -p .
So I do this, but unfortunately this gives me an error saying -bash: android: command not found. I understand this, because "android" as such doesn't refer to anything on my laptop (Mac OSX). So I thought it is maybe referring to the adb. So I tried replacing android for the direct path to my adb:
/Users/kramer65/dev/adt-bundle-mac-x86_64-20130917/sdk/platform-tools/adb update project -t android-17 -p .
This gives me a humongous output with more information on adb, which is I guess not the expected result.
So my questions; what does android refer to, and how can I fix this on Mac OSX?

The android tool is located in the tools directory in your SDK. You need to add this to your PATH environment variable so that bash can recognize it.
You can do this by adding it to your PATH in your .bash_profile file. This file should be located in your home directory. Create if it doesn't exist using vi .bash_profile and add the following line to it:
export PATH=<path_to_android_sdk>/platform-tools:<path_to_android_sdk>/tools:$PATH
where <path_to_android_sdk> is to be replaced with the path to your SDK. For example: "/Users/me/android-sdk-mac_86/platform-tools"

Step 0
The first step is install Android SDK: https://developer.android.com/studio
I don't like the default configurations. I installed SDK in this folder:
/Users/<Username>/Android\ SDK
ℹ️ The default path is
$HOME/Library/Android/sdk
Step 1
The next command open your bash or zshrc configuration file:
Bash profile:
vim ~/.bash_profile
If you use zsh:
vim ~/.zshrc
Step 2
You're ready to update your configurations:
# File: .bash_profile | .zshrc
# Custom path to Android SDK folder.
# If you use the default configuration please change ANDROID_HOME to $HOME/Library/Android/sdk
export ANDROID_HOME=/Users/<Username>/Android\ SDK
export PATH=$ANDROID_HOME/tools:$PATH
export PATH=$ANDROID_HOME/platform-tools:$PATH
Step 3
Option 1:
Restart your terminal and you should be able to use android command
Option 2: source your bash or zsh profile.
Example: source ~/.bash_profile / source ~/.zshrc

I spent so much time trying to figure out, this steps helped me ( from http://docs.phonegap.com/en/2.2.0/guide_getting-started_android_index.md.html )
You need to execute your .bash_profile to update your PATH.
Set up your PATH environment variable on Mac OS
Open the Terminal program (this is in your Applications/Utilites folder by default).
Run the following command
touch ~/.bash_profile; open ~/.bash_profile
This will open the file in the your default text editor.
You need to add the path to your Android SDK platform-tools and tools directory. In my example I will use "/Development/android-sdk-macosx" as the directory the SDK is installed in. Add the following line:
export PATH=${PATH}:/Development/android-sdk-macosx/platform-tools:/Development/android-sdk-macosx/tools
Save the file and quit the text editor. Execute your .bash_profile to update your PATH:
source ~/.bash_profile
Now every time you open the Terminal program you PATH will included the Android SDK.

Problem Solved For Android Studio Users:
I am using Mac OS X Elcapitan version 10.11.X.
Under my home directory I found .bash_profile.save file. I opened that file using sublime (you can use any other editor). Then I added this line
export PATH=${PATH}:/Users/UserName/Library/Android/sdk/platform-tools:/Users/UserName/Library/Android/sdk/tools
Replace "UserName" with your UserName.
open terminal then run
source ~/.bash_profile
here you go.

First add these lines to your ~/.bashrc file:
export ANDROID_HOME=${HOME}/Library/Android/sdk
export PATH=${PATH}:${ANDROID_HOME}/tools
export PATH=${PATH}:${ANDROID_HOME}/platform-tools
then:
source ~/.bashrc

export PATH="/Users/me/Library/Android/sdk/platform-tools/":"/Users/me/Library/Android/sdk/tools/":$PATH
Worked for me

Add the following lines into ~/.bash_profile and source ~/.bash_profile
export ANDROID_HOME=/Users/macbook/Library/Android/sdk/
export PATH=$ANDROID_HOME/tools:$PATH
export PATH=$ANDROID_HOME/platform-tools:$PATH
This is working for me

Update the path.
Open the Terminal program from Spotlight. Run the following command:
touch ~/.bash_profile; open ~/.bash_profile
Then save following code
export PATH=${PATH}:/android-sdk-macosx/platform-tools:/Development/android-sdk-macosx/tools
For my case, path is
export PATH=/Users/<user-name>/Development/android-sdk-macosx/platform-tools:/Users/<user-name>/Development/android-sdk-macosx/tools:$PATH
Save the file and quit the text editor. Execute your .bash_profile to update your PATH:
source ~/.bash_profile
Then run adb.

This is the issue because of you didn't give proper android sdk path variable in .bash_profile. for this you must follow the below steps.
1. Check android sdk path: for this you should open android studio->preferences and click on Android SDK in newly open window in that look for Android SDK location textfield in that you can find path of Android SDK. For me it shows like: /Users/<your_name>/Library/Android/sdk. here <your_name> is name of your home directory.
2. Open your terminal enter cd ~ command.
3. and enter vi .bash_profile.
4. In vi editor enter following
export ANDROID_HOME=/Users/Murali/Library/Android/sdk
export PATH=$ANDROID_HOME/tools:$PATH
export PATH=$ANDROID_HOME/platform-tools:$PATH
Save it by press esc button and enter :wq.
5. After this close your terminal and open it again.
6. To apply all your changes in .bash_profile enter following command
source .bash_profile.
7. Enter android command. Hope this now working fine :-)

Update the path.
Open the Terminal program from Spotlight. Run the following command:
touch ~/.zshrc (or ~/.bash_profile) ; open ~/.zshrc (or ~/.bash_profile)
Then save following code
export AAPT_HOME=/Users/****/Library/Android/sdk/build-tools/31.0.0
export PATH=$PATH:$AAPT_HOME
Save the file and quit the text editor. Execute your .zshrc (or .bash_profile) to update your PATH:
source ~/.zshrc (or ~/.bash_profile)

adb command not found

I need to run an adb forward command before I could use the ezkeyboard application which allows user to type on the phone using browser.
When I run adb forward tcp:8080 tcp:8080 command I get the adb command not found error message.
I can run android command from terminal. Why adb is not working?

In my case with Android Studio 1.1.0 path was this
/Users/<username>/Library/Android/sdk/platform-tools
Add the following to ~/.bash_profile
export PATH=~/Library/Android/sdk/tools:$PATH
export PATH=~/Library/Android/sdk/platform-tools:$PATH
Then run
$ source ~/.bash_profile
to load a profile in a current terminal session, or just reopen a terminal
If you are using more modern Z Shell instead of Bash, put it in ~/.zprofile instead.

Is adb installed? To check, run the following command in Terminal:
~/Library/Android/sdk/platform-tools/adb
If that prints output, skip these following install steps and go straight to the final Terminal command I list:
Launch Android Studio
Launch SDK Manager via Tools -> Android -> SDK Manager
Check Android SDK Platform-Tools
Run the following command on your Mac and restart your Terminal session:
echo export "PATH=~/Library/Android/sdk/platform-tools:$PATH" >> ~/.bash_profile
Note: If you've switched to zsh, the above command should use .zshenv rather than .bash_profile

Make sure adb is in your user's $PATH variable.
or
You can try to locate it with whereis and run it with ./adb

I am using Mac 10.11.1 and using android studio 1.5,
I have my adb
"/Users/user-name/Library/Android/sdk/platform-tools"
Now edit you bash_profile
emacs ~/.bash_profile
Add this line to your bash_profile, and replace the user-name with your username
export PATH="$PATH:/Users/user-name/Library/Android/sdk/platform-tools"
save and close.
Run this command to reload your bash_profile
source ~/.bash_profile

From the file android-sdks/tools/adb_has_moved.txt:
The adb tool has moved to platform-tools/
If you don't see this directory in your SDK, launch the SDK and AVD
Manager (execute the android tool) and install "Android SDK
Platform-tools"
Please also update your PATH environment variable to include the
platform-tools/ directory, so you can execute adb from any location.
so on UNIX do something like:
export PATH=$PATH:~/android-sdks/platform-tools

This is the easiest way and will provide automatic updates.
install homebrew
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
Install adb
brew install --cask android-platform-tools
Start using adb
adb devices

Type the below command in terminal:
nano .bash_profile
And add the following lines (replace USERNAME with your own user name).
export ANDROID_HOME=/Users/USERNAME/Library/Android/sdk
export PATH=${PATH}:${ANDROID_HOME}/tools
export PATH=${PATH}:${ANDROID_HOME}/platform-tools
Close the text editor, and then enter the command below:
source .bash_profile

If you don't want to edit PATH variable, go to the platform-tools directory where the SDK is installed, and the command is there.
You can use it like this:
Go to the directory where you placed the SDK:
cd /Users/mansour/Library/Developer/Android/sdk/platform-tools
Type the adb command with ./ to use it from the current directory.
./adb tcpip 5555
./adb devices
./adb connect 192.168.XXX.XXX

For mac users with zshrc file (who don't have bash profile).
Go to your user folder and tap cmd + fn + shift + "." (on Mac laptop keyboard !)
Hidden files are visible, open .zhrc file with a Text Editor
Paste this line, don't forget to change the username between braces :
export PATH="$PATH:/Users/{username}/Library/Android/sdk/platform-tools"
you can save and close the .zhrc
Open terminal and reload the file with this :
source ~/.zshrc
Now you can use adb command lines !

Considering you have already downloaded SDK platform tools. These commands are for MAC users.
This command will set ADB locally. So if you close the terminal and open it again, ADB commands won't work until you run this command again.
export PATH=~/Library/Android/sdk/platform-tools:$PATH
These commands will set ADB globally. So once you run these commands no need to set them again next time.
echo 'export PATH=$PATH:~/Library/Android/sdk/platform-tools/' >> ~/.bash_profile
source ~/.bash_profile

Mac users just open /Users/(USERNAME)/.bash_profile this file in a editor.
and add this line to add path.
export PATH="/Users/myuser/Library/Android/sdk/platform-tools":$PATH
this is the default path if you install adb via studio.
and dont forget to change the username in this line.

You need to install adb first,
the new command (in 2021) is:
brew install --cask android-platform-tools

In my case, I was in the platform-tools directory but was using command in the wrong way:
adb install
instead of the right way:
./adb install

On my Mac (OS X 10.8.5) I have adb here:
~/Library/android-sdk-mac_86/platform-tools
So, edit the $PATH in your .bash_profile and source it.

+ The reason is: you are in the wrong directory (means it doesn't contain adb executor).
+ The solution is (step by step):
1) Find where the adb was installed. Depend on what OS you are using.
Mac, it could be in: "~/Library/Android/sdk/platform-tools"
or
Window, it could be in: "%USERPROFILE%\AppData\Local\Android\sdk\platform-tools\".
However, in case you could NOT remember this such long directory, you can quickly find it by the command "find". Try this in your terminal/ command line, "find / -name "platform-tools" 2> /dev/null" (Note: I didn't test in Window yet, but it works with Mac for sure).
*Explain the find command,
Please note there is a space before the "/" character --> only find in User directory not all the computer.
"2> /dev/null" --> ignore find results denied by permission. Try the one without this code, you will understand what I mean.
2) Go to where we installed adb. There are 3 ways mentioned by many people:
Change the PATH global param (which I won't recommend) by: "export PATH=~/Library/Android/sdk/platform-tools" which is the directory you got from above. Note, this command won't print any result, if you want to make sure you changed PATH successfully, call "export | grep PATH" to see what the PATH is.
Add more definition for the PATH global param (which I recommend) by: "export PATH=~/Library/Android/sdk/platform-tools:$PATH" or "export PATH=$PATH:~/Library/Android/sdk/platform-tools"
Go to the path we found above by "cd ~/Library/Android/sdk/platform-tools"
3) Use adb:
If you change or update the PATH, simply call any adb functions, since you added the PATH as a global param. (e.g: "adb devices")
If you go to the PATH by cd command, call adb functions with pre-fix "./ " (e.g: "./ adb devices")

I solved this issue by install adb package. I'm using Ubuntu.
sudo apt install adb
I think this will help to you.

If you are using a mac, try this below command.
source $HOME/.bash_profile

in my case I added the following line in my terminal:
export PATH="/Users/Username/Library/Android/sdk/platform-tools":$PATH
make sure that you replace "username" with YOUR user name.
hit enter then type 'adb' to see if the error is gone. if it is, this is what you should see:
Android Debug Bridge version 1.0.40
...followed by a bunch of commands..and ending with this:
$ADB_TRACE
comma-separated list of debug info to log:
all,adb,sockets,packets,rwx,usb,sync,sysdeps,transport,jdwp
$ADB_VENDOR_KEYS colon-separated list of keys (files or directories)
$ANDROID_SERIAL serial number to connect to (see -s)
$ANDROID_LOG_TAGS tags to be used by logcat (see logcat --help)
if you get that, run npm run android again and it should work..

To avoid rewriting the $PATH variables every time you start a terminal, edit your .bash_profile (for Macs, it's just .profile) file under your home directory (~/), and place the export statement somewhere in the file.
Now every time you start terminal, your $PATH variable will be correctly updated. To update the terminal environment immediately after modifying the profile file, type in:
source ~/.profile

nano /home/user/.bashrc
export ANDROID_HOME=/psth/to/android/sdk
export PATH=$PATH:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools
However, this will not work for su/ sudo. If you need to set system-wide variables, you may want to think about adding them to /etc/profile, /etc/bash.bashrc, or /etc/environment.
ie:
nano /etc/bash.bashrc
export ANDROID_HOME=/psth/to/android/sdk
export PATH=$PATH:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools

This solution is for Mac:
Considering you have already downloaded SDK platform tools & trying to set adb path:
If you want to check the SDK is available or not, just check it by following this path:
User > Library (Hidden folder) > Android > sdk > platform-tools > adb
SDK PATH IMAGE
To set the PATH for the adb command on a macOS system, firstly need to edit your shell configuration file. The default shell on macOS is Bash or Zash.
If you're using Bash, so you will need to edit the ~/.bash_profile file otherwise edit ~/.zprofile in your home directory.
Here's how to do it:
By Terminal:
Open a terminal window and enter the following command:
nano ~/.bash_profile
or
nano ~/.zprofile
This will open the ~/.bash_profile or ~/.zprofile file in the Nano text editor.
Add the following line to the file:
export PATH=~/Library/Android/sdk/tools:$PATH
export PATH=~/Library/Android/sdk/platform-tools:$PATH
Press Ctrl+X to exit the Nano editor, then press Y to save the changes and Enter to confirm the filename.
Run the following command to reload your shell configuration:
source ~/.bash_profile
or
source ~/.zprofile
After you have set the PATH for adb, you should be able to run the adb command from any terminal window.
By Manual:
Go to the Home directory & tap command + shift + . (on Mac system/laptop)
View IMAGE
Search file ~/.bash_profile or ~/.zprofile & open it.
View IMAGE
Add required path & save it.
View IMAGE
export PATH=~/Library/Android/sdk/tools:$PATH
export PATH=~/Library/Android/sdk/platform-tools:$PATH
Run the following command to reload your shell configuration:
source ~/.bash_profile
or
source ~/.zprofile
After you have set the PATH for adb, you should be able to run the adb command from any terminal window.

Make sure you have adb installed
To install it you could run the "sudo apt install adb".
You could also try revoking any USB authorizations on your device and
try connecting with USB debugging enabled.

UNABLE TO LOCATE ADB #SOLVED
Simply Download Sdk platform tools.https://developer.android.com/studio/releases/platform-tools.html
Extract the Downloaded file.
Go to Sdk Manager in Android Studio and copy the link. Go to file Explorer and paste the path for Sdk you copied to view the Sdk files. You will notice that the Adb file is missing, open downloaded file (platform tools) copy contents and replace every content in your Sdk tool file (the file where you noticed adb is missing)and save. You are good to go.

In my case this is the solving of this problem
Make sure you have installed the android SDK. Usually the location of SDK
is located to this location
/Users/your-user/Library/Android/sdk
After that cd to that directory.
Once you are in that directory type this command
./platform-tools/adb install your-location-of apk

if youd dont have adb in folder android-sdk-macosx/platform-tools/ you should install platform tools first. Run android-sdk-macosx/tools/android and Install platform tools from Android SDK manager.

you have to move the adb command to /bin/ folder
in my case:
sudo su
mv /root/Android/Sdk/platform-tools/adb /bin/

If you are using fish:
fish_add_path /Users/<name>/Library/Android/sdk/platform-tools/
Or you can add the same to ~/.config/fish/config.fish
Might need to re start the shell

Add the following command to .zshrc file
Open file in terminal using command -> vi .zshrc
Add the android sdk path - > exportPATH="/Users/<user>/Library/Android/sdk/platform-tools:$PATH"
Close the file by -> Esc + :wq

Robotium from command line on Mac

I'm testing Android application, and I want to run Robotium test from Terminal on Mac. As I've read I use adb shell am instrument -w com.test.test1/android.test.InstrumentationTestRunner
Terminal says "-bash: adb: command not found".
Probably, I don't see something obvious, but I'm really just studying. What am I missing?

It seems like you don't have your Environment Variables set properly. You need to cd into the directory of your android sdk and then go to platform-tools folder. Once you are in there you will be able to use adb.
here is more information (Goto the part where it talks about environment variables in "Exploring the SDK section"
On Linux, edit your ~/.bash_profile or ~/.bashrc file. Look for a line that sets the PATH environment variable and add the full path to the tools/ and platform-tools/ directories to it. If you don't see a line setting the path, you can add one:
export PATH=${PATH}:/tools:/platform-tools
On a Mac OS X, look in your home directory for .bash_profile and proceed as for Linux. You can create the .bash_profile if you don't already have one.

Not able to access adb in OS X through Terminal, "command not found"

I have installed Android SDK and Eclipse on my Mac system. I am able to program using Eclipse and have created few sample applications. But I am still not able to access adb through the terminal window. I have tried following command in terminal:
$ pwd
/Users/espireinfolabs/Desktop/soft/android-sdk-mac_x86/platform-tools
$ ls
NOTICE.txt dexdump llvm-rs-cc-2
aapt dx llvm-rs-cc.txt
adb lib source.properties
aidl llvm-rs-cc
$ adb --help
-bash: adb: command not found
I have also added the ls output so that you know in which window I am.

The problem is: adb is not in your PATH. This is where the shell looks for executables. You can check your current PATH with echo $PATH.
Bash will first try to look for a binary called adb in your Path, and not in the current directory. Therefore, if you are currently in the platform-tools directory, just call
./adb --help
The dot is your current directory, and this tells Bash to use adb from there.
But actually, you should add platform-tools to your PATH, as well as some other tools that the Android SDK comes with. This is how you do it:
Find out where you installed the Android SDK. This might be (where $HOME is your user's home directory) one of the following (or verify via Configure > SDK Manager in the Android Studio startup screen):
Linux: $HOME/Android/Sdk
macOS: $HOME/Library/Android/sdk
Find out which shell profile to edit, depending on which file is used:
Linux: typically $HOME/.bashrc
macOS: typically $HOME/.bash_profile
With Zsh: $HOME/.zshrc
Open the shell profile from step two, and at the bottom of the file, add the following lines. Make sure to replace the path with the one where you installed platform-tools if it differs:
export ANDROID_HOME="$HOME/Android/Sdk"
export PATH="$ANDROID_HOME/tools:$ANDROID_HOME/tools/bin:$ANDROID_HOME/platform-tools:$PATH"
Save the profile file, then, re-start the terminal or run source ~/.bashrc (or whatever you just modified).
Note that setting ANDROID_HOME is required for some third party frameworks, so it does not hurt to add it.

For zsh users. Add alias adb='/Users/$USER/Library/Android/sdk/platform-tools/adb' to .zshrc file.
Then run source ~/.zshrc command

run command in terminal nano $HOME/.zshrc
Must include next lines:
export PATH=$PATH:~/Library/Android/sdk/platform-tools
export ANDROID_HOME=~/Library/Android/sdk
export PATH="$HOME/.bin:$PATH"
export PATH="~/Library/Android/sdk/platform-tools":$PATH
Press Ctrl + X to save file in editor,Enter Yes or No and hit Enter key
Run source ~/.zshrc
Check adb in terminal, run adb

In addition to slhck, this is what worked for me (mac).
To check where your sdk is located.
Open Android studio and go to:
File -> Project Structure -> Sdk location
Copy the path.
Create the hidden .bash_profile in your home.
(open it with vim, or open -e) with the following:
export PATH=/Users/<Your session name>/Library/Android/sdk/platform-tools:/Users/<Your session name>/Library/Android/sdk/tools:$PATH
Then simply use this in your terminal: . ~/.bash_profile
SO post on how to find adb devices

Quick Answer
Pasting this command in terminal solves the issue in most cases:
** For Current Terminal Session:
(in macOS) export PATH="~/Library/Android/sdk/platform-tools":$PATH
(in Windows) i will update asap
** Permanently:
(in macOS) edit the ~/.bash_profile using vi ~/.bash_profile and add this line to it: export PATH="~/Library/Android/sdk/platform-tools":$PATH
However, if not, continue reading.
Detailed Answer
Android Debug Bridge, or adb for short, is usually located in Platform Tools and comes with
Android SDK, You simply need to add its location to system path. So system knows about it, and can use it if necessary.
Find ADB's Location
Path to this folder varies by installation scenario, but common ones are:
If you have installed Android Studio, path to ADB would be: (Most Common)
(in macOS) ~/Library/Android/sdk/platform-tools
(in Windows) i will update asap
If you have installed Android Studio somewhere else, determine its location by going to:
(in macOS) Android Studio > Preferences > Appearance And Behavior > System Settings > Android SDK and pay attention to the box that says: Android SDK Location
(in Windows) i will update asap
However Android SDK could be Installed without Android studio, in this case your path might be different, and depends on your installation.
Add it to System Path
When you have determined ADB's location, add it to system, follow this syntax and type it in terminal:
(in macOS)
export PATH="your/path/to/adb/here":$PATH
for example: export PATH="~/Library/Android/sdk/platform-tools":$PATH

I don't know how did you install the android SDK. But in Mac OS, what really worked for me is to reinstall it using brew. All problems solved in a row.
brew install --cask android-sdk
Later on:
android update sdk --no-ui --filter 'platform-tools'
Like a charm

This is how it worked for me
first I find my platform-tools than I was using zshrc instead of bash_profile so I run this command first
echo 'export PATH=${PATH}:$HOME/Library/Android/sdk/platform-tools/' >> ~/.zshrc
next refresh terminal
source ~/.zshrc
Check if it worked
adb devices
result of this command must be something similar to this if so then it worked.
List of devices attached
emulator-5554 device

For me, I ran into this issue after switching over from bash to zsh so I could get my console to look all awesome fantastic-ish with Hyper and the snazzy theme. I was trying to run my react-native application using react-native run-android and running into the op's issue. Adding the following into my ~.zshrc file solved the issue for me:
export ANDROID_HOME=~/Library/Android/sdk
export PATH=${PATH}:${ANDROID_HOME}/tools:${ANDROID_HOME}/platform-tools

If you have installed Android Studio on MAC here is how:
nano ~/.zshrc
or
open ~/.zshrc in VScode
Then edit the file
# Android ADB
export ANDROID_HOME="$HOME/Library/Android/sdk"
export PATH="$ANDROID_HOME/tools:$ANDROID_HOME/tools/bin:$ANDROID_HOME/platform-tools:$PATH"
control + X OR Save file.
Restart Terminal and try
> adb

UPDATE
As #Loren.A mentioned in comment latest version of brew does not support cast. So one can simply use:
brew install android-platform-tools
Simply install adb with brew
brew cask install android-platform-tools
Check if adb is installed
adb devices

If you are using the Mac with the M1 chip add the below export command to the zshrc file using the nano command, if that file is not present the nano command will create it for you so run
nano ~/.zshrc
paste this path in that file without any modification
export PATH="/Users/$USER/Library/Android/sdk/platform-tools":$PATH
hit ctrl-x and then Hit y to save the changes and the hit return Key to close it without renaming the file.
then run
source ~/.zshrc
to refresh the .zshrc file
and then try runnning
adb
it should give you the desired output

If you are using zsh on an OS X, you have to edit the zshrc file.
Use vim or your favorite text editor to open zshrc file:
vim ~/.zshrc
Paste the path to adb in this file:
export PATH="/Users/{$USER}/Library/Android/sdk/platform-tools":$PATH

For Mac OS Catalina or Mojave
Enter command to open nano editor
nano $HOME/.zshrc
Set PATH variable, means append more path as shown here
FLUTTER_HOME="/Users/pankaj/Library/Android/flutter-sdk/flutter/bin"
DART_HOME="/Users/pankaj/Library/Android/flutter-sdk/flutter/bin/cache/dart-sdk/bin"
ANDROID_SDK_HOME="/Users/pankaj/Library/Android/sdk"
ANDROID_ADB_HOME="/Users/pankaj/Library/Android/sdk/platform-tools"
PATH="$PATH:$FLUTTER_HOME"
PATH="$PATH:$DART_HOME"
PATH="$PATH:$ANDROID_SDK_HOME"
PATH="$PATH:$ANDROID_ADB_HOME"
Now press Command + X to save file in editor,Enter Yes or No and hit Enter key.

This worked for me on my MAC - 2020
Go to directory containing adb:
cd ~/Library/Android/sdk/platform-tools/
Run adb command to list all services
./adb shell dumpsys activity services

I couldn't get the stupid path working so I created an alias for abd
alias abd ="~/Library/Android/sdk/platform-tools/adb"
works fine.

For Mac, Android Studio 3.6.1, I added this to .bash_profile
export PATH="~/Library/Android/sdk/platform-tools/platform-tools":$PATH

Or the alternative solution could be
Make sure you already install for android SDK. Usually it is located under
/Users/your-user-name/Library/Android/sdk
If the SDK is there then run this command. ./platform-tools/adb install your-apk-location
From there you can generate the APK file That's the only sample to check if adb
command is there

For some reason when installed Android Studio 3.6.1 the adb file was actually in $ANDROID_HOME/platform-tools/platform-tools. not sure if this is a bug with my installation or what but this fixed it for me.

For Mac Os the default shell has moved on to "zsh" from "bash" as of Mojave and later releases, so for all the Mac users I would suggest go with the creating ".zshrc" file. "adb" runs as it is intended to be. Thanks #slhck for your info.!

Follow steps below
Open bash_profile using open -e .bash_profile
write
export PATH="$ANDROID_HOME/tools:$ANDROID_HOME/tools/bin:$ANDROID_HOME/platform-tools:$PATH"
close bash_profile file
run source .bash_profile
Done run your adb command now !!
In some cases, you may need to run source .bash_profile every time you open cmd to run adb commands

It's working fine..
brew install android-sdk
Later on:
android update sdk --no-ui --filter 'platform-tools'