Conditional operators
Conditional operators are operators useful allowing different commands to be interconnected. For example, using conditionnal operators a command can be executed only upon failure of another command.
Synopsis
command1 operator command2 ...
Run two commands linked by a conditional operator:
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command1, command2 : Two valid pBat commands.
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operator : An operator linking command1 and command2.
Operators type
There is four types of conditional operators:
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& : No condition. Command2 gets executed after command1.
This operator is not really interesting as the same result can be achieved by placing both commands on separates names (through the use of parenthesis for FOR and IF commands), achieving also a higher readability.
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&& : Run command2 if the last executed command returned on success. To determine if an error occured, pBat uses the value of the %ERRORLEVEL% variable fixed by the last executed command :
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if %ERRORLEVEL% is zero, then the command completed successfully.
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else the command returned on error.
if the last executed command returned upon a failure, command2 is ignored and pBat tries to run any of the subsequent commands following rules associated with each of the conditional operators.
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|| : Run command2 if the last executed command returned upon a failure.
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| : Connects command1 standard output to command2 standard input and run both simultaneously.
As both commands are executed simultaneously, the process pBat forks and a child interpreter is created. While command2 runs on the parent interpreter, command1 is executed on the child. Once command1 exits, the child interpreter dies and the script execution continues on the parent intepreter.
Thus, if a command1 modifies pBat environment variable, the changes will not affect the parent interpretor, and the environment of the parent will be left unchanged. As an example:
set example=1 | more test.txtwill not assign the %example% variable. However, command2 can actually change environment variables of the parent interpreter. As an example:
more test.txt | set /p example=will assign the %example% variable.
This behaviour is the opposite of cmd.exe, but it seem more worthwhile to keep the current behaviour as it make possible to assign easily the output of a command to a variable.
Obviously, there is no limitation in the number of conditional operators that can be used in a single line.
FOR and IF behaviour
The FOR and IF are two special command because they change the precedence of conditional operator. By default, if there is no block encountered, then all the operator have the same priority.
This is not true using IF or FOR as they swallow all the commands on theirs right-side, acting as if a block was surrounding the command up to the end of the line.
This also means that the scope of the IF or the FOR commands start from the command up to the end of the command-line. For example, the following code will loop over command1&command2 instead of looping over command1 and then executing command2:
for %%A in (1 2 3 4 5 6 7 8 9 10) do command1&command2
To prevent IF or FOR from swallowing every command up to the end of the command-line, enclose the command in a block, as follows:
(for %%A in (1 2 3 4 5 6 7 8 9 10) do command1) & command2
Compatibility
Available since 0.5.0.0.
Compatible with cmd.exe, except for the order of process in pipes.