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POHow to write a powershell function that wraps a sed/perl/etc command
 

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  1. POHow to write a powershell function that wraps a sed/perl/etc command
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    <p>I have a number of sed/perl/etc "one-liner" commands that I use frequently:</p> <ul> <li><code>head -1</code> (Print the first line of a file)</li> <li><code>sed $d</code> (Drop the last line of a file)</li> <li><code>perl -pe '$_ = qq($. $_)'</code> (Number lines in a file)</li> </ul> <p>You get the idea.</p> <p>All of these commands have the same behaviour - they can take input from standard input, or work on a series of files whose names are passed as arguments. I'd like to wrap these common scripts up as Powershell functions, so that I don't have to remember the exact syntax to use. However, aliases don't work like that, and if I do the "obvious" approach with functions:</p> <pre><code>function numlines { perl -pe '$_ = qq($. $_)' $args } </code></pre> <p>it works with files as arguments (<code>numlines my_file.pl</code>) but not with input from a pipe (<code>cat my_file.pl | numlines</code>).</p> <p>Is there a way to write the function so that it works both ways?</p> <p>To clarify - I can use bat files to do this. For example, numlines.bat containing</p> <pre><code>@perl -pe "$_ = qq($. $_)" %* </code></pre> <p>but having to invoke cmd.exe and the general ugliness of bat files (that "Terminate batch job (Y/N)?" prompt when you hit CTRL-C :-() makes me wish for a similarly simple solution within Powershell...</p> <hr> <p>Based on Richard's suggestion below, I tried:</p> <pre><code>function test { [CmdletBinding()] param( [Parameter(mandatory=$true, ValueFromPipeline=$true)] $data ) process { perl -pe '$_ = qq($. $_)' } } </code></pre> <p>If I then do <code>test file.txt</code> (which I'd want to run effectively identically to <code>perl -pe '$_ = qq($. $_)' file.txt</code>) the function runs, but waits for data on standard input rather than processing <code>file.txt</code>. The same thing happens when I try <code>cat file.txt | test</code> - which I'd expect to act identically to <code>cat file.txt | perl -pe '$_ = qq($. $_)'</code>.</p>
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    1. USPaul Moore
    1. USPaul Moore
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    1. COI know this doesn't answer your original question but try `wc -l` to count the number of lines in a file. It'll take input from a pipe or you can specify the filename directly.
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      1. POHow to write a powershell function that wraps a sed/perl/etc command
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