How to ignore escape sequences stored in PowerShell string variable?

Question

In my PowerShell script, I'm running Select-String over a number of files, looking for a string passed into it via a variable ($id):

foreach ($file in (ls "path\to\files")) {
    $found = $false
    $found = Select-String -Path $file $id -Quiet
    if ($found) {
        break
    }
}

Unfortunately, the $id variable sometimes things like "\C" or "\T", which Select-String tries to interpret as escape sequences. These are not valid escape sequences, so Select-String throws an error. They are not intended to be escape sequences (e.g., it could be part of a file path such as "C:\Test"), so how can I prevent PowerShell/Select-String from interpreting them as such? I've tried using parentheses around $id with no luck.

Adam Plocher · Accepted Answer · 2014-10-12 07:07:56Z

32

Use the static escape() method, it instructs the regular expression engine to interpret these characters literally rather than as metacharacters:

$id = [regex]::escape($id)

You can also turn the command to a one liner (-path can take a collection of files):

Select-String -Path path\to\files\\* -Pattern ([regex]::escape($id)) -Quiet

edited Oct 12, 2014 at 7:07

Adam Plocher

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answered Feb 9, 2009 at 12:11

Shay Levy

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4 Comments

Tomalak Over a year ago

I'd give another +1 for the one-liner, if I could up-vote twice. :-)

alastairs Over a year ago

Sadly the one-liner doesn't work for the specific situation - I cut out a -Filter and a -Recurse parameter

Shay Levy Over a year ago

In that case: dir path\to\files -r | Select-String -Pattern ([regex]::escape($id)) -Quiet -list

mklement0 Over a year ago

[regex]::escape() is indeed the method to use to treat strings as literals (verbatim) in the context of a regular expression in general, but with Select-String specifically, the simpler solution is to use the -SimpleMatch switch.

Bruce Payette · Accepted Answer · 2018-03-23 19:07:39Z

1

Select-String has a -SimpleMatch parameter that will cause the cmdlet to do simple string matches instead of regular expressions. If you change the script to do:

 $found = Select-String -Path $file $id -Quiet -SimpleMatch

it should work as desired.

answered Mar 23, 2018 at 19:07

Bruce Payette

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Comments

codybartfast · Accepted Answer · 2009-02-09 12:32:51Z

If the $id string already contains something like TAB when it's passed to you then I'm not aware of a built in method to safely escape it back to "\t". You need to make sure your script is passed the correct string in the first place. I.e. it needs to passed 0x5C74 (\t) not 0x09 (TAB). So the escaping needs to be done when the the search string is first defined.

Regex.Escape will escape TAB -> \t but will also escape any of these characters that have meaning within regular expressions:

\, *, +, ?, |, {, [, (,), ^, $,., #, and white space

e.g. . -> \.

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