PowerShell: Piping Output and Input

By Xah Lee. Date: 2009-07-17

PowerShell lets you send one command's output to the next command's input, called piping. This is similar to the idea of nesting functions, but using a linear syntax.

For example, suppose you have function f, g, h, and you want to compute “h(g(f(x)))”. The nested syntax is inconvenient to use. With post-fix notation, for example used in bash, you can write it as: “x | f | g | h”. This is called a pipe, because it is analogous to water flowing thru pipes.

Here are some examples:

# list current dir, sort it
dir | sort

# list, sort, show first 5 elements
dir | sort | select -first 5

# list, sort, select, then format for display
dir | sort | select -first 5 | format-table name, length

# list help topics with summary
Get-Help about* | Select-Object Name,Synopsis | Format-Table -Auto

# moving png image files to another dir
Get-Item $HOME/Documents/*png | Move-Item -Destination $HOME/Pictures/

# filter out bot access from web log, save to file
get-content web-log.txt |
select-string -notmatch "Googlebot" |
out-file -Encoding utf8 -width 999000 web-log2.txt

# piping example on showing processes
Get-Process | Select-Object Name

Get-Process | Sort-Object ID -descending

Get-Process |
Where-Object { $_.Handles -ge 500 } |
Sort-Object Handles |
Format-Table Handles,Name,Description -Auto

Note that the output of PowerShell are .NET objects. They display on screen as formatted text representation. Unlike unix shells, it is not passing text streams.

# using get-member to see object's members
dir | get-member