Bugs in a production environment are stressful. The search for context information typically starts by searching the log files. It can be tedious to find the context you’re looking for in (rotated) log files or you’re pushing a large amount of data to your logs.

A nice thing about grep is that it can search for a pattern in multiple files at the same time. Simultaneously search in selected files or use a glob pattern that resolves all files for you. This tutorial shows you how to search in multiple log files using grep.

Ubuntu/Debian Series Overview

Search in Selected Log Files with grep

grep allows you to search for a pattern in more than one file. You may search in selected log files if your application sends logs to different files. For example, you may search your default app.log and an extra delete-audit.log file. Add your selected files as separate arguments to grep:

grep "pattern" storage/logs/app.log storage/logs/delete-audit.log  

Search in all .log Files with grep

You can also use a glob pattern to search within all files having the .log file extension. The following line searches for the given pattern in all log files within the storage/logs directory. It won’t search through subdirectories and stay on the selected directory’s level to pick the files:

grep "pattern" storage/logs/*.log  

Examples

Here’s a sample output of how grep prints the matches to the console. Notice that a matching line is printed with the prefixed log file name. This helps you detect what log file could have more details:

$ grep "request" storage/logs/*.log
storage/logs/app.log:INFO: ======= request finished successful ======> {"took":"0.052s","status_code":200}  
storage/logs/delete-audit.log:DEBUG: User deletion requested {"userId":"1"}  
storage/logs/delete-audit.log:DEBUG: User successfully deleted {"userId":"1"}  

That’s it!