Error reporting in git====================== `die`, `usage`, `error`, and `warning` report errors of variouskinds. - `die` is for fatal application errors.  It prints a message to  the user and exits with status 128. - `usage` is for errors in command line usage.  After printing its  message, it exits with status 129.  (See also `usage_with_options`  in the link:api-parse-options.html[parse-options API].) - `error` is for non-fatal library errors.  It prints a message  to the user and returns -1 for convenience in signaling the error  to the caller. - `warning` is for reporting situations that probably should not  occur but which the user (and Git) can continue to work around  without running into too many problems.  Like `error`, it  returns -1 after reporting the situation to the caller. Customizable error handlers--------------------------- The default behavior of `die` and `error` is to write a message tostderr and then exit or return as appropriate.  This behavior can beoverridden using `set_die_routine` and `set_error_routine`.  Forexample, "git daemon" uses set_die_routine to write the reason `die`was called to syslog before exiting. Library errors-------------- Functions return a negative integer on error.  Details beyond thatvary from function to function: - Some functions return -1 for all errors.  Others return a more  specific value depending on how the caller might want to react  to the error. - Some functions report the error to stderr with `error`,  while others leave that for the caller to do. - errno is not meaningful on return from most functions (except  for thin wrappers for system calls). Check the function's API documentation to be sure. Caller-handled errors--------------------- An increasing number of functions take a parameter 'struct strbuf *err'.On error, such functions append a message about what went wrong to the'err' strbuf.  The message is meant to be complete enough to be passedto `die` or `error` as-is.  For example: 	if (ref_transaction_commit(transaction, &err))		die("%s", err.buf); The 'err' parameter will be untouched if no error occurred, so multiplefunction calls can be chained: 	t = ref_transaction_begin(&err);	if (!t ||	    ref_transaction_update(t, "HEAD", ..., &err) ||	    ret_transaction_commit(t, &err))		die("%s", err.buf); The 'err' parameter must be a pointer to a valid strbuf.  To silencea message, pass a strbuf that is explicitly ignored: 	if (thing_that_can_fail_in_an_ignorable_way(..., &err))		/* This failure is okay. */		strbuf_reset(&err);