How do I capture the output into a variable from an external process in PowerShell

Question

I d like to run an external process and capture it s command output to a variable in PowerShell   I m currently using this    params     verify  pc  domain hosp uhhg org  start-process  netdom exe   params -WindowStyle Hidden -Wait   I ve confirmed the command is executing but I need to capture the output into a variable   This means I can t use the -RedirectOutput because this only redirects to a file

User · Answer

Another real-life example    result    amp    env cust tls store Tools WDK x64 devcon exe  enable  strHwid 2 gt  amp 1   Out-String   Notice that this example includes a path  which begins with an environment variable   Notice that the quotes must surround the path and the EXE file  but not the parameters   Note  Don t forget the  amp  character in front of the command  but outside of the quotes   The error output is also collected   It took me a while to get this combination working  so I thought that I would share it

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This thing worked for me    scriptOutput    cmd  s  c  FilePath  ArgumentList

User · Answer

I use the following  Function GetProgramOutput  string  exe   string  arguments         process   New-Object -TypeName System Diagnostics Process      process StartInfo FileName    exe      process StartInfo Arguments    arguments           process StartInfo UseShellExecute    false      process StartInfo RedirectStandardOutput    true      process StartInfo RedirectStandardError    true      process Start             output    process StandardOutput ReadToEnd           err    process StandardError ReadToEnd             process WaitForExit             output      err         exe    quot C  Program Files 7-Zip 7z exe quot   arguments    quot i quot        runResult    GetProgramOutput  exe  arguments   stdout    runResult -2   stderr    runResult -1        System Console   WriteLine  quot Standard out   quot     stdout   System Console   WriteLine  quot Standard error   quot     stderr

User · Answer

If you want to redirect the error output as well  you have to do    cmdOutput   command 2 gt  amp 1   Or  if the program name has spaces in it    cmdOutput    amp   command with spaces  2 gt  amp 1

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If all you are trying to do is capture the output from a command  then this will work well   I use it for changing system time  as  timezoneinfo   local always produces the same information  even after you have made changes to the system  This is the only way I can validate and log the change in time zone    NewTime    powershell exe -command  timezoneinfo   local   NewTime   Tee-Object -FilePath  strLFpath  strLFName -Append   Meaning that I have to open a new PowerShell session to reload the system variables

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I got the following to work    Command1  C   ProgramData Amazon Tools ebsnvme-id exe   result    amp  invoke-Expression  Command1   Out-String    result gives you the needful

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Note  The command in the question uses Start-Process  which prevents direct capturing of the target program s output  Generally   do not use Start-Process to execute console applications synchronously - just invoke them directly  as in any shell  Doing so keeps the application connected to the calling console s standard streams  allowing its output to be captured by simple assignment  output   netdom      as detailed below  Fundamentally  capturing output from external programs works the same as with PowerShell-native commands  you may want a refresher on how to execute external programs   lt command gt  is a placeholder for any valid command below    cmdOutput    lt command gt      captures the command s success stream   stdout output  Note that  cmdOutput receives an array of objects if  lt command gt  produces more than 1 output object  which in the case of an external program means a string 1  array containing the program s output lines  If you want to make sure that the result is always an array - even if only one object is output  type-constrain the variable as an array  or wrap the command in      the array-subexpression operator    array   cmdOutput    lt command gt    or   cmdOutput      lt command gt    By contrast  if you want  cmdOutput to always receive a single - potentially multi-line - string  use Out-String  though note that a trailing newline is invariably added    Note  Adds a trailing newline   cmdOutput    lt command gt    Out-String  With calls to external programs - which by definition only ever return strings in PowerShell 1  -  you can avoid that by using the -join operator instead    NO trailing newline   cmdOutput     lt command gt   -join  quot  n quot   Note  For simplicity  the above uses  quot  n quot  to create Unix-style LF-only newlines  which PowerShell happily accepts on all platforms  if you need platform-appropriate newlines  CRLF on Windows  LF on Unix   use  Environment   NewLine instead   To capture output in a variable and print to the screen   lt command gt    Tee-Object -Variable cmdOutput   Note how the var name is NOT  -prefixed  Or  if  lt command gt  is a cmdlet or advanced function  you can use common parameter -OutVariable   -ov   lt command gt  -OutVariable cmdOutput     cmdlets and advanced functions only  Note that with -OutVariable  unlike in the other scenarios    cmdOutput is always a collection  even if only one object is output  Specifically  an instance of the array-like  System Collections ArrayList  type is returned  See this GitHub issue for a discussion of this discrepancy   To capture the output from multiple commands  use either a subexpression          or call a script block           with  amp  or     cmdOutput      lt command gt           subexpression   cmdOutput    amp    lt command gt          script block with  amp  - creates child scope for vars    cmdOutput       lt command gt          script block with   - no child scope  Note that the general need to prefix with  amp   the call operator  an individual command whose name path is quoted  - e g    cmdOutput    amp   netdom exe      - is not related to external programs per se  it equally applies to PowerShell scripts   but is a syntax requirement  PowerShell parses a statement that starts with a quoted string in expression mode by default  whereas argument mode is needed to invoke commands  cmdlets  external programs  functions  aliases   which is what  amp  ensures  The key difference between        and  amp                      is that the former collects all input in memory before returning it as a whole  whereas the latter stream the output  suitable for one-by-one pipeline processing   Redirections also work the same  fundamentally  but see caveats below    cmdOutput    lt command gt  2 gt  amp 1   redirect error stream  2  to success stream  1   However  for external commands the following is more likely to work as expected   cmdOutput   cmd  c  lt command gt   2 gt  amp 1    Let cmd exe handle redirection - see below    Considerations specific to external programs   External programs  because they operate outside PowerShell s type system  only ever return strings via their success stream  stdout   similarly  PowerShell only ever sends strings to external programs via the pipeline  1   Character-encoding issues can therefore come into play   On sending data via the pipeline to external programs  PowerShell uses the encoding stored in the  OutVariable preference variable  which in Windows PowerShell defaults to ASCII    and in PowerShell  Core  to UTF-8   On receiving data from an external program  PowerShell uses the encoding stored in  Console   OutputEncoding to decode the data  which in both PowerShell editions defaults to the system s active OEM code page   See this answer for more information  this answer discusses the still-in-beta  as of this writing  Windows 10 feature that allows you to set UTF-8 as both the ANSI and the OEM code page system-wide       If the output contains more than 1 line  PowerShell by default splits it into an array of strings  More accurately  the output lines are stored in an array of type  System Object    whose elements are strings   System String     If you want the output to be a single  potentially multi-line string  use the -join operator  you can alternatively pipe to Out-String  but that invariably adds a trailing newline    cmdOutput     lt command gt   -join  Environment   NewLine  Merging stderr into stdout with 2 gt  amp 1  so as to also capture it as part of the success stream  comes with caveats   To do this at the source  let cmd exe handle the redirection  using the following idioms  works analogously with sh on Unix-like platforms    cmdOutput   cmd  c  lt command gt   2 gt  amp 1          array  of strings  typically   cmdOutput    cmd  c  lt command gt   2 gt  amp 1   -join  quot  r n quot    single string  cmd  c invokes cmd exe with command  lt command gt  and exits after  lt command gt  has finished   Note the single quotes around 2 gt  amp 1  which ensures that the redirection is passed to cmd exe rather than being interpreted by PowerShell   Note that involving cmd exe means that its rules for escaping characters and expanding environment variables come into play  by default in addition to PowerShell s own requirements  in PS v3  you can use special parameter --   the so-called stop-parsing symbol  to turn off interpretation of the remaining parameters by PowerShell  except for cmd exe-style environment-variable references such as  PATH    Note that since you re merging stdout and stderr at the source with this approach  you won t be able to distinguish between stdout-originated and stderr-originated lines in PowerShell  if you do need this distinction  use PowerShell s own 2 gt  amp 1 redirection - see below     Use PowerShell s 2 gt  amp 1 redirection to know which lines came from what stream   Stderr output is captured as error records   System Management Automation ErrorRecord    not strings  so the output array may contain a mix of strings  each string representing a stdout line  and error records  each record representing a stderr line   Note that  as requested by 2 gt  amp 1  both the strings and the error records are received through PowerShell s success output stream    Note  The following only applies to Windows PowerShell - these problems have been corrected in PowerShell  Core  v6   though the filtering technique by object type shown below     -is  System Management Automation ErrorRecord   can also be useful there   In the console  the error records print in red  and the 1st one by default produces multi-line display  in the same format that a cmdlet s non-terminating error would display  subsequent error records print in red as well  but only print their error message  on a single line   When outputting to the console  the strings typically come first in the output array  followed by the error records  at least among a batch of stdout stderr lines output  quot at the same time quot    but  fortunately  when you capture the output  it is properly interleaved  using the same output order you would get without 2 gt  amp 1  in other words  when outputting to the console  the captured output does NOT reflect the order in which stdout and stderr lines were generated by the external command   If you capture the entire output in a single string with Out-String  PowerShell will add extra lines  because the string representation of an error record contains extra information such as location  At line      and category    CategoryInfo       curiously  this only applies to the first error record   To work around this problem  apply the  ToString   method to each output object instead of piping to Out-String   cmdOutput    lt command gt  2 gt  amp 1          ToString      in PS v3  you can simplify to   cmdOutput    lt command gt  2 gt  amp 1     ToString  As a bonus  if the output isn t captured  this produces properly interleaved output even when printing to the console    Alternatively  filter the error records out and send them to PowerShell s error stream with Write-Error  as a bonus  if the output isn t captured  this produces properly interleaved output even when printing to the console               cmdOutput    lt command gt  2 gt  amp 1   ForEach-Object     if     -is  System Management Automation ErrorRecord         Write-Error        else                   1  As of PowerShell 7 1  PowerShell knows only strings when communicating with external programs  There is generally no concept of raw byte data in a PowerShell pipeline  If you want raw byte data returned from an external program  you must shell out to cmd exe  c  Windows  or sh -c  Unix   save to a file there  then read that file in PowerShell  See this answer for more information

User · Answer

I tried the answers  but in my case I did not get the raw output  Instead it was converted to a PowerShell exception   The raw result I got with    rawOutput    cmd  c  lt command gt  2  gt   amp 1

User · Answer

Or try this  It will capture output into variable  scriptOutput    amp   netdom exe   params   Tee-Object -Variable scriptOutput   Out-Null   scriptOutput

User · Answer

Have you tried    OutputVariable    Shell command    Out-String

[powershell] How do I capture the output into a variable from an external process in PowerShell?

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