Command-Line Tools: cut and grep

Command-Line Tools: cut, grep, cat, sort, uniq

• cut: Extracts specific sections from each line of input, based on fields, bytes, or characters
  • Flags:
    • -d [delimiter]: Specifies a delimiter (default is tab) for splitting lines
    • -f [fields]: Extracts specific fields (e.g., -f1,3 for fields 1 and 3)
    • -b [bytes]: Extracts specific byte positions (e.g., -b1-5 for the first five bytes)
    • -c [characters]: Extracts specific character positions (e.g., -c1-3 for the first three characters)
  • Examples:
    • Extract the first column (default delimiter is tab): cut -f1 file.txt
    • Extract the 2nd and 4th fields from a CSV file: cut -d',' -f2,4 data.csv
    • Extract the first 5 characters from each line: cut -c1-5 file.txt
  • With Pipes: Combines with grep to search and extract fields: grep "pattern" file.txt | cut -d',' -f1

grep

• Searches for patterns in text files or input streams.
  • Flags:
    • -i: Case-insensitive search
    • -v: Invert match (exclude lines matching the pattern)
    • -E: Enables extended regular expressions (like egrep)
    • -r: Recursively search files in a directory
    • -n: Displays line numbers with matching lines
    • -c: Counts the number of matches
    • -o: Shows only the matching part of the lines
  • Examples:
    • Find lines containing "error" (case-insensitive): grep -i "error" log.txt
    • Exclude lines containing "warning": grep -v "warning" log.txt
    • Display matching lines with line numbers: grep -n "error" log.txt
  • With Pipes: Searches for a pattern in the output of another command: cat file.txt | grep "search term"

cat

• Displays, concatenates, or redirects file contents.
  • Flags:
    • -n: Numbers all lines
    • -b: Numbers non-empty lines only
    • -s: Suppresses repeated empty lines
    • -E: Displays $ at the end of each line (for visualizing line endings)
  • Examples:
    • Display file contents: cat file.txt
    • Concatenate two files into one: cat file1.txt file2.txt > combined.txt
    • Display file contents with line numbers: cat -n file.txt
  • With Pipes: Combines files and searches for a pattern: cat file1.txt file2.txt | grep "pattern"

sort

• Sorts lines of text files or input.
  • Flags:
    • -r: Sorts in reverse order
    • -n: Sorts numerically (e.g., 1, 2, 10 instead of 1, 10, 2)
    • -u: Removes duplicates (unique lines)
    • -t [delimiter]: Uses a specific delimiter for sorting fields
    • -k [key]: Sorts based on a specific field (e.g., -k2 for the second field)
  • Examples:
    • Sorts lines alphabetically: sort file.txt
    • Sorts numerically: sort -n numbers.txt
    • Sorts by the second column (fields separated by commas): sort -t',' -k2 file.csv
  • With Pipes: Sorts output from another command: grep "pattern" file.txt | sort -r

uniq

• Filters out or processes adjacent duplicate lines
  • Flags:
    • -c: Counts occurrences of unique lines
    • -d: Prints only duplicate lines
    • -u: Prints only unique lines
    • -i: Ignores case when comparing lines
  • Examples:
    • Removes duplicate lines: uniq file.txt
    • Counts occurrences of each line: uniq -c file.txt
    • Prints only duplicate lines: uniq -d file.txt
  • With Pipes: Sorts lines first, then removes duplicates: sort file.txt | uniq

Combining Tools

• The power of these commands lies in using pipelines (|) and redirection (> or >>).
• Example: Extracts the first column, sorts, and counts occurrences from a CSV using pipelines.

This quiz covers essential command-line tools like 'cut' and 'grep'. Learn how to extract specific sections from text lines and search for patterns using flags and examples. Master these tools to enhance your command-line skills.