Hack.md

Hack

Hackish tips and snippets.

Single script to run in both Windows batch and Linux Bash

Single line script

Use CMD label trick:

• The label character, a colon (:), is equivalent to true in most POSIXish shells
• CMD will ignore lines that start with : (label character)

:; echo "Hi, I’m ${SHELL}."; exit $?
@ECHO OFF
ECHO I'm %COMSPEC%

Don’t forget that any use of $? must be before your next colon : because : resets $? to 0.

Multi line script

Use heredoc trick:

:; echo "I am ${SHELL}"
:<<"::CMDLITERAL"
ECHO I am %COMSPEC%
::CMDLITERAL
:; echo "And ${SHELL} is back!"
:; exit
ECHO And back to %COMSPEC%

Use heredoc with GOTO trick:

:<<"::CMDLITERAL"
@ECHO OFF
GOTO :CMDSCRIPT
::CMDLITERAL

echo "I can write free-form ${SHELL} now!"
if :; then
  echo "This makes conditional constructs so much easier because"
  echo "they can now span multiple lines."
fi
exit $?

:CMDSCRIPT
ECHO Welcome to %COMSPEC%

Universal comment

Universal comments, of course, can be done with the character sequence : # or :;#. The space or semicolon are necessary because sh considers # to be part of a command name if it is not the first character of an identifier.

: # This is a special script which intermixes both sh
: # and cmd code. It is written this way because it is
: # used in system() shell-outs directly in otherwise
: # portable code. See https://stackoverflow.com/questions/17510688
: # for details.
:; echo "This is ${SHELL}"; exit
@ECHO OFF
ECHO This is %COMSPEC%

reference

• https://stackoverflow.com/a/17623721