Searching and Extracting Data Flashcards

Which grep option uses extended regular expressions without needing to escape special characters like `+` or `|`?

Answer: grep -E

grep -E (or egrep) enables extended regular expressions, allowing unescaped use of +, |, (, and ).

What does `find . -type d` search for?

Answer: Directories only

The -type d predicate restricts find results to directories.

Which command sorts a file numerically by the second field, using a comma as delimiter?

Answer: sort -t, -k2 -n file

sort -t, sets comma as delimiter, -k2 selects the second field, and -n sorts numerically.

What is the effect of `tr -d '\n'` on its input?

Answer: Deletes all newline characters from the input

tr -d deletes every occurrence of the specified character; here it removes all newline characters.

Which command finds files that were accessed more than 7 days ago?

Answer: find . -atime +7

find -atime +7 finds files whose last access time was more than 7 days ago.

What does the `grep -l 'error' *.log` command output?

Answer: Only the names of .log files that contain 'error'

grep -l prints only the filenames of files that contain at least one match, not the matching lines.

Which pipeline lists the ten most frequently occurring words in a text file?

Answer: cat file | sort | uniq -c | sort -rn | head -10

Splitting into words, counting with uniq -c, reverse-numeric sorting, then head -10 gives the top 10 most frequent words.