watch: Repeat Commands and See Changes

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# Run command every 2 seconds (default)
watch date

# Run every 5 seconds
watch -n 5 date

# Run every 0.5 seconds
watch -n 0.5 date

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# Highlight differences between updates
watch -d df -h

# Highlight changes permanently (cumulative)
watch -d=cumulative df -h

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-n, --interval    Seconds between updates (default: 2)
-d, --differences Highlight changes
-t, --no-title    Hide the header
-b, --beep        Beep on command error
-e, --errexit     Exit on command error
-c, --color       Interpret ANSI color sequences
-x, --exec        Pass command to exec instead of sh -c

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# Watch disk usage
watch df -h

# Watch specific mount
watch 'df -h | grep /dev/sda1'

# Watch directory size
watch 'du -sh /var/log'

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# Memory stats
watch free -h

# Memory with buffers/cache detail
watch 'free -h && echo && cat /proc/meminfo | head -10'

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# Process count
watch 'ps aux | wc -l'

# Specific process
watch 'ps aux | grep nginx'

# Process memory
watch 'ps aux --sort=-%mem | head -10'

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# Network connections
watch 'netstat -tuln'

# Connection count
watch 'netstat -an | wc -l'

# Active connections
watch 'ss -s'

# Interface stats
watch 'cat /proc/net/dev'

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# File list
watch ls -la

# Directory size changes
watch 'du -sh *'

# File count
watch 'find . -type f | wc -l'

# Recent files
watch 'ls -lt | head -10'

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# Container status
watch docker ps

# Container stats
watch 'docker stats --no-stream'

# Image list
watch docker images

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# Pod status
watch kubectl get pods

# All resources
watch 'kubectl get pods,svc,deploy'

# Pod logs (last 5 lines)
watch 'kubectl logs -l app=myapp --tail=5'

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# Branch status
watch git status

# Log (one line per commit)
watch 'git log --oneline -10'

# Diff stats
watch git diff --stat

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# Last log lines
watch 'tail -5 /var/log/syslog'

# Error count
watch 'grep -c ERROR /var/log/app.log'

# Recent errors
watch 'grep ERROR /var/log/app.log | tail -5'

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# HTTP health check
watch 'curl -s localhost:8080/health'

# API response time
watch 'curl -s -w "%{time_total}\n" -o /dev/null http://localhost/api'

# Service status
watch systemctl status nginx

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# PostgreSQL connections
watch 'psql -c "SELECT count(*) FROM pg_stat_activity"'

# MySQL process list
watch 'mysql -e "SHOW PROCESSLIST"'

# Table row count
watch 'psql -c "SELECT count(*) FROM users"'

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# Single quotes (preferred)
watch 'ps aux | grep nginx | wc -l'

# Double quotes (allows variable expansion)
watch "df -h | grep $MOUNT"

# Multiple commands
watch 'echo "=== Disk ===" && df -h && echo "=== Memory ===" && free -h'

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# Without exec: may have quoting issues
watch ls -la /tmp

# With exec: cleaner
watch -x ls -la /tmp

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# Exit when command fails
watch -e 'curl -f http://localhost/health'

# Beep on error (non-zero exit)
watch -b 'systemctl is-active myservice'

# Exit when output changes (use with diff)
watch -g 'cat /etc/passwd | md5sum'

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watch 'dmesg | tail -20 | grep -i error'

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watch "free | awk '/Mem:/ {printf \"%.1f%%\n\", \$3/\$2*100}'"

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watch 'curl -s localhost:8080/metrics | jq .requests_total'

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while true; do
    clear
    date
    df -h
    sleep 2
done

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# Install
brew install viddy  # macOS
go install github.com/sachaos/viddy@latest

# Use (better diff, time machine, etc.)
viddy -d df -h

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# Run command when files change
ls *.py | entr python test.py

# Clear screen and run
ls *.py | entr -c python test.py

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watch -t 'date +%H:%M:%S'

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watch -c 'ls --color=always'
watch -c 'grep --color=always ERROR /var/log/app.log | tail -10'

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# Exact intervals (compensates for command runtime)
watch -p -n 1 date +%s.%N

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# Can't redirect watch output directly, but can log the command
watch 'df -h | tee -a disk.log'