grep - Search text using patterns.
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Options:
-i: Ignore case distinctions.-r: Read all files under each directory, recursively.-v: Invert match to select non-matching lines.-n: Prefix each line of output with the line number within its input file.-l: Print file names with matches, once for each file.-c: Suppress normal output, counting lines matching instead.
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Example:
grep -i "error" /var/log/syslog # search for 'error' in '/var/log/syslog', ignoring case
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Common Use Cases:
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Search for a string in a file:
grep "hello" file.txt -
Search recursively in directories:
grep -r "pattern" /path/to/dir -
Count matching lines:
grep -c "pattern" file.txt
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