7 useful grep commands

Grep is a command-line utility that allows you to search for patterns in text files. Here are some common grep commands and their explanations:

1. grep 'error' logfile.txt: This command searches the file logfile.txt for lines that contain the word "error".
2. grep -r 'error' /var/log: This command searches the /var/log directory and all subdirectories for files that contain the word "error". The -r option stands for "recursive."
3. grep -v 'warning' logfile.txt: This command searches the file logfile.txt for lines that do not contain the word "warning". The -v option stands for "invert match."
4. grep -i 'ERROR' logfile.txt: This command searches the file logfile.txt for lines that contain the word "ERROR", ignoring the case of the characters. The -i option stands for "ignore case."
5. grep -c 'error' logfile.txt: This command searches the file logfile.txt for lines that contain the word "error" and prints a count of the number of matching lines. The -c option stands for "count."
6. grep -n 'error' logfile.txt: This command searches the file logfile.txt for lines that contain the word "error" and prints the line numbers of the matching lines. The -n option stands for "line number."
7. grep -l 'error' *.log: This command searches all files with the .log extension in the current directory for lines that contain the word "error" and prints only the names of the files that contain a match, rather than the matching lines themselves. The -l option stands for "files with matches."