Linux Text Processing Cheat Sheet

cat app.log | grep ERROR

# Basic pipeline for filtering text from a file.

grep ERROR app.log

# Prefer direct file arguments when possible.

journalctl -u nginx | awk '{print $1, $2, $3}'

# Many text tools consume stdin naturally.

grep ERROR app.log | tee errors.txt | wc -l

# Write output to a file while still passing it downstream.

ps aux 
  | grep python 
  | grep -v grep 
  | awk '{print $2, $11}'

# Use backslashes for readability.

head -n 20 server.log

# Preview the top of a file.

tail -n 50 server.log

# Read the end of a file.

tail -f /var/log/nginx/access.log

# Watch new lines as they are appended.

sed -n '100,120p' file.txt

# Extract lines 100 through 120.

awk 'NR>=100 && NR<=120' file.txt

# Alternative line-range extraction using NR.

tr -s ' ' < input.txt

# Collapse multiple spaces into one.

sed 's/^[[:space:]]*//' file.txt

# Remove spaces and tabs from the start of each line.

sed 's/[[:space:]]*$//' file.txt

# Remove spaces and tabs from line endings.

fmt -w 72 README.txt

# Reflow long text paragraphs.

fold -w 80 long-lines.txt

# Break long lines at a fixed width.