Read file line by line in PowerShell

Question

I want to read a file line by line in PowerShell  Specifically  I want to loop through the file  store each line in a variable in the loop  and do some processing on the line   I know the Bash equivalent   while read line do     if     line     regex     then             work here     fi done  lt  file txt   Not much documentation on PowerShell loops

User · Answer

Get-Content has bad performance  it tries to read the file into memory all at once   C    NET  file reader reads each line one by one  Best Performace  foreach  line in  System IO File   ReadLines  C  path to file txt              line     Or slightly less performant   System IO File   ReadLines  C  path to file txt     ForEach-Object                 The foreach statement will likely be slightly faster than ForEach-Object  see comments below for more information

User · Answer

I was able to read a 4GB log file in about 50 seconds with the following  You may be able to make it faster by loading it as a C  assembly dynamically using PowerShell   System IO StreamReader  sr    System IO File   Open  file   System IO FileMode   Open  while  -not  sr EndOfStream        line    sr ReadLine      sr Close

User · Answer

Not much documentation on PowerShell loops    Documentation on loops in PowerShell is plentiful  and you might want to check out the following help topics  about For  about ForEach  about Do  about While   foreach  line in Get-Content   file txt        if  line -match  regex             Work here           Another idiomatic PowerShell solution to your problem is to pipe the lines of the text file to the ForEach-Object cmdlet   Get-Content   file txt   ForEach-Object       if    -match  regex             Work here             Instead of regex matching inside the loop  you could pipe the lines through Where-Object to filter just those you re interested in   Get-Content   file txt   Where-Object     -match  regex    ForEach-Object         Work here

User · Answer

The almighty switch works well here   one two three   gt  file   regex     t   switch -regex -file file       regex    quot line is    quot        Output  line is two line is three

[powershell] Read file line by line in PowerShell

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