Search for Text from the Linux Terminal

grep is one of the standard Linux tools for searching text in files or command output.

Search One File

grep 'error' application.log

Search Several Files

grep 'TODO' *.py

Ignore Case

grep -i 'warning' /var/log/syslog

Show Line Numbers

grep -n 'function' script.js

Search Recursively

grep -rI 'main' ./src

-r walks subdirectories and -I skips binary files.

Invert the Match

grep -v 'DEBUG' application.log

This prints lines that do not match the pattern.

Search Command Output

Pipes let grep filter another program’s output:

ps aux | grep '[n]ginx'

For process names, dedicated tools such as pgrep are often better:

pgrep -a nginx

Avoid Unnecessary cat

Instead of:

cat file.txt | grep 'text'

prefer:

grep 'text' file.txt

Both work, but passing the filename directly is simpler.

Literal Strings

If the search text contains regex metacharacters and should be interpreted literally, use -F:

grep -F 'config[value]' file.txt

Conclusion

Use grep for quick text searches and combine options such as -i, -n, -r, -v, and -F to match the job. For more complex patterns, switch to extended regular expressions with grep -E.