A day at batch scripting

Documentation: An A-Z Index of the Windows CMD command line
Tutorial: Batch Script Tutorial

• string comparison in IF is by default case sensitive. To make it case insensitive, use the /i switch. (source)
• if the last line of your code before a closing parentheses is a ::comment, like this:
  

  @echo off
  IF 1==1 (
   echo 1
   echo 2
   ::echo 3
  )

  then you'll get this error:
  

  ) was unexpected at this time.

• if the script stops after executing a command to a command line tool (i.e. npm install ), you're probably calling it without CALL. You should call it with CALL (i.e. CALL npm install). (source)
• hidden files and folders do not get detected with FOR %%a in (*) or in FOR /D %%a in (*). Here's how to query for hidden fires/folders.
• Use @echo off to avoid printing every executed line.
• if you do a SETLOCAL make sure to use ENDLOCAL at the end
• variables (source):
• SET foo=1 --> set environmental variable
  %foo% --> refer to environmental variable
  !foo! --> refer to environmental variable with delayed expansion
• %%a --> FOR loop variable referred to in batch script
  %a --> FOR loop variable referred to in command line
• variable declaration and spaces and quotes -- pay attention to these.
• delayed expansion: (source and example) --> use it if you need to create and modify variables within loops.
  

  @echo off
  setlocal enabledelayedexpansion
  set searchfor=a c
  for %%a in (a b c d) do (
      set item="%%a"
   set found=0
   ( for %%b in (%searchfor%) do (
    set candidate="%%b"
    if "!item!"=="!candidate!" (
     set found=1
    )
   )
   )
   if "!found!"=="0" (
    echo "!item!" did not match any of the search terms
   ) else (
    echo "!item!" was a match
   )
  )
  endlocal

• functions
• documentation: read here. 
• maximum length of a label is not 8 characters anymore
• execution order: (source)
  it is very important to do the navigation with goto :eof and goto :end. If these navigations are left out it can cause code segments to run multiple times
  

  @echo off
  call :foo
  call :foo2
  goto end
  
  :foo
   echo foo
   goto :eof
  :foo2
   echo foo2
   goto :eof
  :end
   echo done

• processing input arguments (source for foo; source for foo2)
  

  @echo off
  call :foo 1 2 3
  call :foo2 a b c
  goto end
  
  :foo
   for %%a in (%*) do (
    echo %%a
   )
   goto :eof
  :foo2
   echo %~1
   echo %~2
   echo %~3
   goto :eof
  :end