The logcat command-line tool is used to display system logs on Android devices. It's invaluable for debugging and monitoring what your application and the Android system are doing.

Basics of Logcat

The basic command to start logcat is:
adb logcat
This will start printing the log data in the console.

Filtering Logs

However, the amount of log data can be overwhelming. Therefore, you can use filters to narrow down the logs.
Filter logs by priority level
Log entries have a tag and a priority associated with them. The priority levels are as follows:
  • V — Verbose (lowest priority)
  • D — Debug
  • I — Info
  • W — Warning
  • E — Error
  • F — Fatal
  • S — Silent (highest priority, on which nothing is ever printed)
You can filter log output by priority level, for example:
adb logcat *:E
This command will print only error messages.
Filter logs by TAG
Every log message has a tag which is usually defined by the class name. If you want to filter out logs from a specific tag, you can use:
adb logcat -s "YourTAG"
Combining TAG and Priority Filters
You can also combine these filters:
adb logcat YourTAG:E *:S
This will print only the error (E) messages for YourTAG and silence (S) everything else.

Searching for Sensitive Information

One of the most basic ways to search for sensitive information in logs is simply to use the grep command. This is not specific to logcat but can be used with it. For example:
adb logcat | grep "password"
This command will show you any log entries that include the word "password". You can replace "password" with any other word you're interested in, such as "token", "key", "pin", etc.