Differences Between grep and pgrep in Linux

pgrep and grep are two different commands in the Linux system. Although their names are similar, they have significant differences in functionality and usage scenarios. Here are their core differences:

pgrep is an acronym that stands for “Process-ID Global Regular Expressions Print”.

grep is an acronym for “Global Regular Expressions Print”, meaning global regular expression print.

1. Functionality

• grep is used to search for lines that match a specific pattern (string or regular expression) in file contents or text streams. For example:
```
grep "error" /var/log/syslog # Search for lines containing "error" in the log file
```
• pgrep is used to find running processes based on process names or other attributes, returning their PID (Process ID). For example:
```
pgrep nginx # Find the PID of the process named "nginx"
```

2. Target Objects

• grep operates on files, command output, or text data passed through pipes.
• pgrep directly queries the system kernel’s process list without needing text parsing.

3. Regular Expression Support

• **grep** supports full regular expressions (basic and extended), for example:
```
grep -E "error|warning" log.txt # Match "error" or "warning"
```
• **pgrep** only supports simple process name matching and does not support complex regular expressions. For exact matches, the -x option is required:
```
pgrep -x "python" # Only match processes whose name is exactly "python"
```

4. Output Results

• grep by default outputs the entire matching line of text, but can use -o to output only the matching part.
• **pgrep** by default only outputs the PID, but can display process names with -l:
```
pgrep -l nginx # Output PID and process name
```

5. Performance and Use Cases

• grep is suitable for static text analysis (such as logs, configuration files), but requires additional filtering when processing process information (e.g., ps aux | grep needs to exclude the grep process itself).
• pgrep directly retrieves process PIDs, making it more efficient, especially for quickly locating processes in scripts.

Summary

Dimension	`<span>grep</span>`	`<span>pgrep</span>`
Usage	Text content search	Process PID lookup
Input Source	Files/Text streams	System process list
Regex Support	Full regular expressions	Simple pattern matching
Output	Matching lines or text fragments	Process PIDs (can display process names)
Typical Scenarios	Log analysis, configuration file search	Process management, script automation

So how much do you know about egrep and fgrep? Feel free to share your insights.