Notepad++ has built-in column editing and Line Up by (,) command (TextFX plugin) giving a graphical point-and-click solution that is likely to be first time right. This avoids having to use regular expressions or shell programming, both of which typically require some debugging till they do exactly what you want and nothing more.
Starting point: CSV file with columns misaligned, so not easy to edit by column...
1,Value1,value2,value3,value4,value5
3445,Value1,value2,value3,value4,value5
12345,Value1,value2,value3,value4,value5
1234,Value1,value2,value3,value4,value5
11,Value1,value2,value3,value4,value5
...
Procedure:
Select the rows of interest -- perhaps the entire file.
Use menu command TextFX > TextFX Edit > Line up Multiple Lines by Comma (,)
This lines up all of the rows by column and makes column editing easy.
1 ,Value1,value2,value3,value4,value5
3445 ,Value1,value2,value3,value4,value5
12345,Value1,value2,value3,value4,value5
1234 ,Value1,value2,value3,value4,value5
11 ,Value1,value2,value3,value4,value5
Enter Column Mode at the column after the first comma (,)
For a small number of rows, use the keyboard commands: Alt+Shift+DownArrow.
If needing to work on many rows (large file), use Alt+mouse and click the desired column of the first line, then move to the last line of the file and Alt+Shift+click the same column position. This activates column mode on the ENTIRE file -- you should see a vertical line behind all the commas.
Delete in column mode removes an entire column of characters. So you can delete everything prior to the first comma in all of the rows all at once to get:
Value1,value2,value3,value4,value5
Value1,value2,value3,value4,value5
Value1,value2,value3,value4,value5
Value1,value2,value3,value4,value5
Value1,value2,value3,value4,value5
Done!
Remark on this solution compared with the various others suggested so far:
Column Mode editing is quite powerful and, when combined with TextFX plugin options, applies to a variety of situations in a point-and-quick way.
For example, if you decided to delete the 2nd column, or the Nth column quickly, this approach works with almost no modification.
Regular expressions, shell scripts, on the other hand, will accomplish the goal, yes, but in complicated problems you'll spend more time "de-bugging" your syntax.
Notepad++'s versatile built-in functionality is one of its main strengths: you get quite a bit of power without having to resort to "programming".