Linux for DevOps

# Basic search
Select-String "ERROR" app.log

# Case-insensitive (default in PS)
Select-String "error" app.log

# Show line numbers (default in PS)
Select-String "WARN" app.log

# Recursive search
Get-ChildItem -Recurse *.log |
  Select-String "OutOfMemory"

# Context lines
Select-String "FATAL" app.log -Context 3,3

# Count matches
(Select-String "ERROR" app.log).Count

# Exclude lines
Get-Content app.log |
  Where-Object {$_ -notmatch "DEBUG"}

# Live follow + filter
Get-Content -Wait app.log |
  Where-Object { $_ -match "ERROR" }

# Last 20 lines
Get-Content app.log | Select -Last 20

# First 10 lines
Get-Content app.log | Select -First 10

# Count lines
(Get-Content app.log).Count

# Pipe + count
(Select-String "ERROR" app.log).Count

# Replace text
(Get-Content config.yml) -replace
  'localhost','prod-db' |
  Set-Content config.yml

# View all env variables
Get-ChildItem Env:
$Env:PATH

# Set temp variable (current session)
$Env:DB_PASSWORD = "mypassword"
$Env:APP_ENV = "staging"

# Use variables
Write-Host $Env:DB_PASSWORD
Write-Host "Running in: $Env:APP_ENV"

# Permanent (User scope)
[System.Environment]::SetEnvironmentVariable(
  "APP_ENV", "production", "User")

# Add to PATH (User scope)
$p = [System.Environment]::GetEnvironmentVariable("PATH","User")
[System.Environment]::SetEnvironmentVariable(
  "PATH", "$p;C:\opt\myapp\bin", "User")

# Unset
Remove-Item Env:DB_PASSWORD

# Check if set
if (-not $Env:MY_VAR) {
  Write-Host "MY_VAR is not set!"
}

# Variables
$AppName = "devops-app"
$Version = "1.0.0"
Write-Host "Deploying $AppName v$Version"

# Command substitution
$Date = Get-Date -Format "yyyy-MM-dd"
$HostName = $env:COMPUTERNAME
Write-Host "Host: $HostName | Date: $Date"

# Conditionals
$AppEnv = $env:APP_ENV
if ($AppEnv -eq "production") {
  Write-Host "Production deployment"
} elseif ($AppEnv -eq "staging") {
  Write-Host "Staging deployment"
} else {
  Write-Host "Unknown environment"
  exit 1
}

# Loops over array
$Services = @("nginx","redis","postgres")
foreach ($svc in $Services) {
  $s = Get-Service $svc -ErrorAction SilentlyContinue
  if ($s -and $s.Status -eq "Running") {
    Write-Host "OK: $svc" -ForegroundColor Green
  } else {
    Write-Host "DOWN: $svc" -ForegroundColor Red
  }
}

# Function
function Test-Port($Port) {
  $c = Test-NetConnection localhost -Port $Port -WA SilentlyContinue
  Write-Host "Port $Port`: $(if($c.TcpTestSucceeded){'OPEN'}else{'CLOSED'})"
}
Test-Port 80
Test-Port 8080

# Create sample log
@"
2024-01-15 08:01 INFO  App started on port 3000
2024-01-15 08:05 WARN  Response time > 500ms
2024-01-15 08:07 ERROR Cache timeout on redis:6379
2024-01-15 08:15 ERROR NullPointerException in UserService
2024-01-15 08:22 WARN  Memory usage at 78%
2024-01-15 09:00 ERROR DB connection pool exhausted
"@ | Set-Content "$env:TEMP\app.log"

# Try these:
Select-String "ERROR" "$env:TEMP\app.log"
(Select-String "ERROR" "$env:TEMP\app.log").Count
Select-String "WARN|ERROR" "$env:TEMP\app.log"
Get-Content "$env:TEMP\app.log" | Where {$_ -notmatch "INFO"}
Get-Content "$env:TEMP\app.log" | Select -Last 3

# Windows Event Log
Get-EventLog Application -EntryType Error -Newest 10