I use the following command in Powershell to convert files in the background but would like to log the results all in one file. Now the -RedirectStandardOutput replaces the file each run.

foreach ($l in gc ./files.txt) {Start-Process -FilePath "c:\Program Files (x86)\calibre2\ebook-convert.exe" -Argumentlist "'$l' '$l.epub'" -Wait -WindowStyle Hidden -RedirectStandardOutput log.txt}

I tried with a redirect but then the log is empty. If possible I would like to keep it a one-liner.

foreach ($l in gc ./files.txt) {Start-Process -FilePath "c:\Program Files (x86)\calibre2\ebook-convert.exe" -Argumentlist "`"$l`" `"$l.epub`"" -Wait -WindowStyle Hidden *> log.txt}

CodePudding user response：

You can use redirection and append to files if you don't use Start-Process, but a direct invocation:

foreach ($l in gc ./files.txt) {& 'C:\Program Files (x86)\calibre2\ebook-convert.exe' "$l" "$l.epub" *>> log.txt}

CodePudding user response：

If sequential, synchronous execution is acceptable, you can simplify your command to use a single output redirection (the assumption is that ebook-convert.exe is a console-subsystem application, which PowerShell therefore executes synchronously (in a blocking manner).:

Get-Content ./files.txt | ForEach-Object {
  & 'c:\Program Files (x86)\calibre2\ebook-convert.exe' $_ "$_.epub" 
} > log.txt

If you want to control the character encoding, use Out-File - which > effectively is an alias for - with its -Encoding parameter; or, preferably, with text output - which external-program output always is in PowerShell - Set-Content.

Note that PowerShell never passes raw output from external programs through to files - they are first always decoded into .NET strings, based on the encoding stored in [Console]::OutputEncoding (the system's active legacy OEM code page by default), and then re-encoded on saving to a file, using the file-writing cmdlet's own defaults, unless overridden with -Encoding - see this answer for more information.

If you want asynchronous, parallel execution (such as via Start-Process, which is asynchronous by default), your best bet is to:

• write to separate (temporary) files:

  • Pass a different output file to -RedirectStandardOutput / -RedirectStandardError in each invocation.

  • Note that if you want to merge stdout and stderr output and capture it in the same file, you'll have to call your .exe file via a shell (possibly another PowerShell instance) and use its redirection features; for PowerShell, it would be *>log.txt; for cmd.exe (as shown below), it would be > log.txt 2>&1

• wait for all launched processes to finish:

  • Pass -PassThru to Start-Process and collect the process-information objects returned.

  • Then use Wait-Process to wait for all processes to terminate; use the -Timeout parameter as needed.

• and then merge them into a single log file.

Here's an implementation:

$procsAndLogFiles = 
  Get-Content ./files.txt | ForEach-Object -Begin { $i = 0 } {
    # Create a distinct log file for each process,
    # and return its name along with a process-information object representing
    # each process as a custom object.
    $logFile = 'log{0:000}.txt' -f   $i
    [pscustomobject] @{
      LogFile = $logFile
      Process = Start-Process -PassThru -WindowStyle Hidden `
                  -FilePath 'cmd.exe' `
                  -ArgumentList '/c', "`"c:\Program Files (x86)\calibre2\ebook-convert.exe`" `"$_`" `"$_.epub`" > `"$logFile`" 2>&1" 
    }
  }

# Wait for all processes to terminate.
# Add -Timeout and error handling as needed.
$procsAndLogFiles.Process | Wait-Process

# Merge all log files.
Get-Content -LiteralPath $procsAndLogFiles.LogFile > log.txt

# Clean up.
Remove-Item -LiteralPath $procsAndLogFiles.LogFile