At some point your script will encounter an error. It could be a failed HTTP request or an attempt to process an invalid file type. MaSH allows you to respond to these errors using the mash.error object and an error block.
The Error Object
When a mashlet encounters an error that error is assigned to the mash.error object. This object has three properties message, line and expression.
Properties
message: String get
A useful message which explains why the error occurred.
line: Number get
The line number of the script where the error occurred.
expression: String get
The line of code within the script which caused the error.
The Error Block
An error block can be placed anywhere in your script and will be called when an error occurs in the previous expression. Error blocks can be extremely helpful, for example we can use them to notify an administrator that a script has failed or call exit which will prevent the script from continuing any further.
Natural
# Make a HTTP request with a deliberately invalid URL
set response to mash.http.get("https://invalid")
error
printline "Error: {{mash.error.message}}"
printline "Line: {{mash.error.line}}"
printline "Expression: {{mash.error.expression}}"
exit
end
# This will not be called
printline "This will not be printed"Standard
# Make a HTTP request with a deliberately invalid URL
response = mash.http.get("https://invalid")
error
printline("Error: {{mash.error.message}}")
printline("Line: {{mash.error.line}}")
printline("Expression: {{mash.error.expression}}")
exit
end
# This will not be called
printline("This will not be printed")
Output
Error: cURL error 6: Could not resolve host: invalid; Unknown error (see https://curl.haxx.se/libcurl/c/libcurl-errors.html) for https://invalid
Line: 3
Expression: set response to mash.http.get("https://invalid")Stopping a script with fail
In our previous script we called exit when an error occurred to halt the script’s execution. By using exit the MaSH runtime assumes that the mashlet executed successfully and your log files will reflect this. Instead we can use a fail statement to halt our script and cause the runtime to log an error instead. Below is the previous script but using fail instead of exit.
Natural
# Make a HTTP request with a deliberately invalid URL
printline "This will be printed"
set response to mash.http.get("https://invalid")
error
fail mash.error.message
end
# This will not be called
printline "This will not be printed"Standard
# Make a HTTP request with a deliberately invalid URL
printline("This will be printed")
response = mash.http.get("https://invalid")
error
fail mash.error.message
end
# This will not be called
printline("This will not be printed")Output
This will be printed