TopolearnPowerShell's dash-style operators and case-insensitive defaults trip up everyone coming from other languages.
Comparison operators are words with a dash, because > and < are redirection: -eq -ne -gt -ge -lt -le. String operators: -like (wildcards * and ?), -match (regex, fills the automatic $Matches variable), -replace (regex replace). Membership: -contains (collection on the left) and -in (collection on the right). All are case-insensitive by default; prefix with c for case-sensitive: -ceq, -cmatch.
A surprise: with a collection on the left, comparison operators filter instead of returning a boolean. 1, 5, 9 -gt 4 returns 5, 9. That is why $null -eq $x is written with $null first.
Branching: if (...) { } elseif (...) { } else { }. switch matches a value against cases and supports -Wildcard, -Regex and script-block conditions. Unlike C, every matching case runs unless you break, and given an array, switch processes each element.
Loops:
foreach ($item in $collection) { }statement: fast, for data already in memory,ForEach-Object { $_ }cmdlet: streams pipeline input one item at a time,for ($i = 0; $i -lt 10; $i++) { },while,do { } while/until.
1..5 is a range, and logical operators are -and, -or, -not (or !).
Example
$n = 7
if ($n -gt 5) { 'big' } elseif ($n -gt 2) { 'medium' } else { 'small' } # big
'Hello' -eq 'hello' # True (case-insensitive by default)
'Hello' -ceq 'hello' # False
'report.csv' -like '*.csv' # True
'v2.15' -match 'v(\d+)\.(\d+)' # True
$Matches[1] # 2
'b' -in 'a', 'b', 'c' # True
1, 5, 9 -gt 4 # 5 / 9 (a collection on the left filters!)
switch -Wildcard ('error.log') {
'*.log' { 'log file' } # log file
'err*' { 'error-ish' } # error-ish (every matching case runs)
}
foreach ($i in 1..3) { "item $i" } # item 1 / item 2 / item 3
$i = 0; while ($i -lt 3) { $i++ }; $i # 3Remember
- -eq -gt -like -match: case-insensitive unless prefixed with c
- A collection on the left of a comparison filters it
- switch runs every matching case; foreach statement vs ForEach-Object cmdlet
Watch out for
- Writing
if ($x > 5): > is redirection and creates a file named 5.