Key Options
Combine various `grep` command options to search for your desired text.
1. Basic Search
2. Search Options
3. Output Options
4. Recursive Search
Generated command:
Try combining the commands.
Description:
`grep` Executes the command.
Combine the above options to virtually execute commands with AI.
Regular Expression Basics
The `grep` command supports Regular Expressions for powerful text searching. Using regular expressions allows you to easily find complex patterns.
| Character | Description | Example |
|---|---|---|
| . | Any single character (except newline) | `a.b` (acb, amb, etc.) |
| * | The preceding character zero or more times | `ab*c` (ac, abc, abbc, etc.) |
| + | The preceding character one or more times | `ab+c` (abc, abbc, etc.) |
| ? | The preceding character zero or one time | `ab?c` (ac, abc) |
| ^ | Start of a line | `^start` (lines beginning with 'start') |
| $ | End of a line | `end$` (lines ending with 'end') |
| [abc] | Any one of the characters in the brackets | `[aeiou]` (vowels) |
| [a-z] | Any character within the specified range | `[0-9]` (digits) |
| [^abc] | Any character NOT in the brackets | `[^0-9]` (non-digit characters) |
| \b | Word boundary | `\bword\b` (exactly the word 'word') |
| | | OR operator (either of two patterns) | `cat|dog` ('cat' or 'dog') |
Basic Regular Expressions (BRE) and Extended Regular Expressions (ERE)
`grep` uses BRE by default. To use characters like `+`, `?`, `|`, `(`, `)` with special meaning, you must escape them with a backslash (`\`). Using the `-E` option enables ERE mode, allowing these characters to be used without backslashes. The `-P` option provides more powerful PCRE.
Usage Examples
Practice text searching through practical examples of the `grep` command.
Search for 'error' in a log file
grep 'error' /var/log/syslogPrints all lines containing the string 'error' in the `syslog` file.
Case-insensitive search for 'failed' and print line numbers
grep -in 'failed' /var/log/auth.logSearches for 'failed' regardless of case and displays line numbers with the results.
Print lines that do not contain a specific pattern
grep -v '^#' /etc/nginx/nginx.confPrints lines from `nginx.conf` file, excluding lines that start with a hash (#) (comments).
Search for 'server_name' in '.conf' files including subdirectories
grep -r 'server_name' *.confRecursively searches for the 'server_name' pattern in files with a '.conf' extension in the current directory and all its subdirectories.
Find a specific process (using ps and pipe)
ps aux | grep apache2Filters and displays only 'apache2' related processes from the output of the `ps aux` command.
Search for 'warning' or 'critical' in multiple files
grep -E 'warning|critical' /var/log/syslog /var/log/kern.logUses the regular expression OR (|) operator to search for 'warning' or 'critical' messages in multiple log files.