GREP and SED with PowerShell

So...I like GREP and SED from my old UNIX days and am VERY happy to see that PowerShell can do the same type of functionality with a lot more power in most cases. I though some of you might like some really simple examples of how to take a text file and do GREP-ish and SED-ish actions.

GREP-ish

cat somefile.txt | where { $_ -match "expression"}

The command above will search each line of "somefile.txt" to see if it contains the regular expression "expression" and return the entire line if there is a match.

SED-ish

cat somefile.txt | %{$_ -replace "expression","replace"}

The command above will search each line of "somefile.txt" for the regular expression "expression" and replace it with the string "replace".

EXAMPLE:

==============DATA.TXT==============

Mary had a little lamb,

It's fleece was white as snow,

But the lamb made Mary mad,

So she ate it.

=================================

GREP-ish

cat DATA.TXT | where { $_ -match "Mary"}

returns the following:

Mary had a little lamb,

But the lamb made Mary mad,

SED-ish

cat DATA.TXT | % { $_ -replace "Mary","Susan" }

returns the following:

Susan had a little lamb,

It's fleece was white as snow,

But the lamb made Susan mad,

So she ate it.

================ Edit 7/14 ==================== 

A question came up the the other day about putting these results into another text file. Using redirection this is quite easy. Here is how it is done:

cat DATA.TXT | % { $_ -replace "Mary","Susan" } > newfile.txt

============================================

enjoy :)

Technorati Tags: regular expressions, grep, sed, match, replace, text file, Mary, little lamb

• Anonymous
  July 08, 2007
  So...I like GREP and SED from my old UNIX days and am VERY happy to see that PowerShell can do the same

• Anonymous
  October 18, 2008
  Why didn't you just port the grep with all it's option, you just did invent the wheel, congrats.

• Anonymous
  October 21, 2008
  Ummm....yeah the point was to show how to do these kinds of activities with PowerShell not to reinvent GREP but thank you for playing :)

• Anonymous
  January 14, 2009
  you can also use select string cat data.txt | select-string -pattern "Mary" which also works on objects, like files so: dir -recurse | select-string -pattern "Mary" will do the grep, and tell you which file it found it in.

• Anonymous
  April 25, 2009
  Thanks very much for this very useful info. It's worth noting that you should use ' instead of " if you want to stop Powershell replacing things with variables in your regular expressions. e.g.  Get-Process | Select Name | sort -property Name | foreach { $_.Name -replace '^(.*)90$', '$1ninety' } will give you a list of sorted process names, changing any names that end with 90 to ninety, such as SQLAGENT90 to SQLAGENTninety.

• Anonymous
  January 03, 2011
  The comment has been removed

• Anonymous
  January 03, 2011
  Claus, Check out the set-content command.  Although I didn't show it here get-content and set-content are very useful.  Here is a link to the command:  technet.microsoft.com/.../dd347736.aspx Z

• Anonymous
  February 26, 2011
  The use of ">" gave me quite a headache as it has weird consequences on the ouput file. I used your example on a xml config file for Tomcat, and I always ended up with a 500 Server error as soon as I used my modified config file. I finally tried something else which worked: cat DATA.TXT | % { $_ -replace "Mary","Susan" } | Set-Content newfile.txt . And just like that, my troubles were gone! I would be really interested in knowing the difference between ">" and "Set-Content", do you have any ideas?

• Anonymous
  February 26, 2011
  The comment has been removed

• Anonymous
  February 28, 2011
  I should have said that I tried copy/pasting the faulty file content into a working file (basically keeping just the file, but overwriting the content) and I had the same issue. To me it is closely related to the file in itself and not the content...

• Anonymous
  March 03, 2015
  The comment has been removed

• Anonymous
  August 03, 2015
  Won't work in Powershell 3.0 To fix it add parenthesis: (cat DATA.TXT) | % { $_ -replace "Mary","Susan" } > newfile.txt

• Anonymous
  September 24, 2015
  The comment has been removed

• Anonymous
  November 24, 2015
  @sp - try piping the results of dir/gci to another foreach loop.  Something like...    dir | %{ $f = $; (cat $f) | %{ $ -replace "Mary","Susan" } > "$f.tmp"; move "$f.tmp" $f -Force  } ...might get you close.  It's not strictly in-place, but it should do the trick.   You can remove the ;move... bit if you want to keep the original files.