Why are placeholders not replaced properly in my strings? - powershell

Question

I have different errors when I am trying to format strings:
$dir = "c:\path"
$logfile = "$dir\logfile_{0}.txt" -f (get-date -format "yyyymmdd_hhmmtt")
Function Log($message) {
$message = "{0}: {1}" -f (get-date) $message
write-host $message
}
Log "Start processing {0}" -f ($_.FullName)
I expect $logfile to be c:\path\logfile_20160616_121012.txt but instead I get formats such as c:\path\logfile_20160116_1201nachm.
I expect Log to output 16.06.2016 12:01:20 Start Processing Myfile.xlsx but instead I get 16.06.2016 12:01:20 Start Processing 16.06.2016 12:01:20
What am I doing wrong?

Answer 1

The tt at the end of your Date formatting string yyyymmdd_hhmmtt, is the AM/PM designator.
Based on the output you receive, you're probably running on an OS with German locale (Nachmittag = PM).
If you want seconds, use ss instead. With no AM/PM designator, you should probably switch to using 24-hour time as well (replace hh with HH).
You can put the date format string inside the placeholder:
"$dir\logfile_{0:yyyymmdd_HHmmss}.txt" -f (Get-Date)
In the Log function, please be aware that the arguments to the -f operator needs to be comma separated.

Answer 2

You are trying to access a pipeline variable at your last line ($_.FullName) but you don't use any pipeline there. You also need to put the format there in parenthesis before you pass the string to the Log function.
You are missing a comma in the format parameters within your Log function:
$dir = "c:\path"
$logfile = "$dir\logfile_{0}.txt" -f (get-date -format "yyyymmdd_hhmmtt")
Function Log($message) {
$message = "{0}: {1}" -f (get-date), $message
write-host $message
}
Log ("Start processing {0}" -f $logfile)