• REGEX
• Sed
  • Add text in the first line of an archive
• Grep
  • Extract email addresses from CSV
  • Count rows matching a field
• Awk
  • Print selected CSV columns
• JQ
  • Extract JSON fields
• Python
  • Search YAML keys by regex

REGEX

Sed

Add text in the first line of an archive

sed -e '1i value1,value2,value3,value4\' csv_1.csv

Grep

Extract email addresses from CSV

grep -Eo '[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}' csv_1.csv

Count rows matching a field

grep -E ',China,' csv_1.csv | wc -l

Awk

Print selected CSV columns

awk -F, 'NR==1 || /China/ { print $1","$4","$5 }' csv_1.csv

JQ

Extract JSON fields

jq -r '.[] | [.name, .email] | @csv' json_1.json

Python

Search YAML keys by regex

python3 -c "import re, pathlib; text=pathlib.Path('yaml_1.yaml').read_text(); print(re.findall(r'^\s*name:\s*(.+)', text, re.M))"

Notes

• grep is useful for quick pattern matching in plain text files.
• awk is useful for field extraction and quick reporting from delimited data.
• jq is the most reliable tool for structured JSON extraction.
• Use python3 when you need richer regex handling or multi-line searches.