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Linux for Production Support Ch 7 / 32 Advanced 🪟 Windows → Linux

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Vijay replaces PowerShell with bash

Bash scripting for PowerShell users — same logic, different syntax

⏱ 14 min 6 commands 5 takeaways

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In this chapter

Vijay

Windows support engineer, month 2 on Linux

The story

By month 2, Vijay was comfortable with Linux day-to-day. But he still switched to his Windows machine for scripting. PowerShell felt natural. Bash felt foreign.

His colleague Meena showed him the translation in one hour.

THE CORE TRANSLATION

PowerShell                          Bash
Write-Host "Hello"                  echo "Hello"
$var = "value"                      var="value"  (no $ on left, no spaces)
Write-Host $var                     echo "$var"
$env:PATH                           $PATH
Get-Date                            date
Get-Date -Format "yyyy-MM-dd"       date +%Y-%m-%d
Start-Sleep 5                       sleep 5
Exit 1                              exit 1

VARIABLES

PowerShell:
$serverName = "prod-server-01"
$today = (Get-Date).ToString("yyyy-MM-dd")

Bash:
serverName="prod-server-01"          # no $ on left, no spaces around =
today=$(date +%Y-%m-%d)              # $() runs a command and captures output

# Reading variables is the same: $variablename
echo "Server: $serverName"

IF STATEMENTS

PowerShell:
if ($diskUsage -gt 90) {
    Write-Host "CRITICAL"
} elseif ($diskUsage -gt 80) {
    Write-Host "WARNING"
} else {
    Write-Host "OK"
}

Bash:
if [ "$diskUsage" -gt 90 ]; then
    echo "CRITICAL"
elif [ "$diskUsage" -gt 80 ]; then
    echo "WARNING"
else
    echo "OK"
fi

Number comparisons: -gt, -lt, -eq, -ne, -ge, -le

String comparisons: = (equal), != (not equal), -z (empty), -n (not empty)

FOR LOOPS

PowerShell:
foreach ($server in @("web-01", "web-02", "web-03")) {
    Test-Connection $server
}

Bash:
for server in web-01 web-02 web-03; do
    ping -c 1 $server
done

# Loop over a range:
PowerShell: 1..10 | ForEach-Object { Write-Host $_ }
Bash:       for i in {1..10}; do echo $i; done

FUNCTIONS

PowerShell:
function Check-Disk {
    param($mount, $threshold)
    return $usage
}

Bash:
check_disk() {
    local mount=$1          # $1 is first argument
    local threshold=$2      # $2 is second argument
    local usage
    usage=$(df "$mount" | awk 'NR==2{print $5}' | tr -d '%')
    echo "$usage"           # return by printing, capture with $()
}
result=$(check_disk "/" 85)

ERROR HANDLING

PowerShell:
try {
    Copy-Item source.txt dest.txt
} catch {
    Write-Error "Copy failed"
    exit 1
}

Bash:
set -euo pipefail           # exit on any error - like try around everything

# Or handle individually:
if ! cp source.txt dest.txt; then
    echo "ERROR: Copy failed" >&2
    exit 1
fi

A REAL SCRIPT TRANSLATION

PowerShell:

$services = @("nginx", "myapp", "postgresql")
$failed = @()
foreach ($svc in $services) {
    if ((Get-Service $svc).Status -ne "Running") {
        $failed += $svc
    }
}
if ($failed.Count -gt 0) { exit 1 }

Bash:

#!/bin/bash
set -euo pipefail
services="nginx myapp postgresql"
failed=""
for svc in $services; do
    if systemctl is-active --quiet "$svc"; then
        echo "OK: $svc"
    else
        echo "DOWN: $svc"
        failed="$failed $svc"
    fi
done
if [ -n "$failed" ]; then
    echo "FAILED:$failed"
    exit 1
fi

SCHEDULED TASKS vs CRON

PowerShell: Register-ScheduledTask with -TriggerAt "06:00"
Linux cron: 0 6 * * * /path/to/script.sh

PowerShell: -RepetitionInterval (New-TimeSpan -Minutes 15)
Linux cron: */15 * * * * /path/to/script.sh

crontab -l              # list scheduled tasks (like Get-ScheduledTask)
crontab -e              # edit scheduled tasks (like Task Scheduler GUI)

Vijay converted his most-used PowerShell scripts to bash over two weekends. By month 3 he was writing bash natively without thinking about PowerShell first.

Key takeaways

Bash variables have no spaces around = and you read them with $ — var=value then echo $var

if/elif/else/fi is identical logic to PowerShell if/elseif/else — just different brackets and keywords

set -euo pipefail at the top replaces try/catch — exits cleanly on any error

Functions receive arguments as $1 $2 — there are no named parameters like PowerShell param()

crontab -e replaces Task Scheduler — minute hour day month weekday is the 5-field cron syntax

Commands from this chapter

$ var=$(command)

PowerShell $var = (command) equivalent — capture command output into variable

$ if [ -z "$var" ]; then

PowerShell if ($var -eq '') equivalent — check if string is empty

$ for item in $list; do ... done

PowerShell foreach ($item in $list) equivalent

$ command || { echo 'failed'; exit 1; }

PowerShell try/catch equivalent — handle command failure

$ crontab -e

Task Scheduler equivalent — edit scheduled tasks

$ set -euo pipefail

PowerShell ErrorActionPreference Stop equivalent — exit on any error