Searching with grep

Finding text with grep

• grep searches for a word and prints only the lines that contain it:

grep error log.txt

• Out of a huge log, you instantly see just the lines that matter.

Useful options

• -i ignores case (so Error matches error).
• -n shows the line number of each match.
• -v inverts — show lines that do not match.

grep -n ok log.txt

grep loves pipes

• grep shines at the end of a pipe, filtering another command's output:

cat log.txt | grep error | wc -l

• "How many error lines?" — filter to errors, then count them. An everyday combo.

Common mistakes

• grep pattern file finds matching lines; add -i to ignore case.
• Quote a pattern that has spaces or special characters.