[Libguestfs] [PATCH 1/2] mllib: allow external_command to return [] on nonzero return value

This is useful for probing probing for cache files such as: external_command ?ignore_error:(Some true) ~prog "ls .cache/something.*" will return command output (matched files) on its success or empty list whenits exit code is other than 0 (there are no such files). --- mllib/common_utils.ml | 15 ++++++++++----- mllib/common_utils.mli | 2 +- 2 files changed, 11 insertions(+), 6 deletions(-) diff --git a/mllib/common_utils.ml b/mllib/common_utils.ml index 76d8b79..9719b16 100644 --- a/mllib/common_utils.ml +++ b/mllib/common_utils.ml @@ -528,23 +528,28 @@ let compare_lvm2_uuids uuid1 uuid2 = loop 0 0 (* Run an external command, slurp up the output as a list of lines. *) -let external_command ~prog cmd = +let external_command ~prog ?(ignore_error = false) cmd = let chan = Unix.open_process_in cmd in let lines = ref [] in (try while true do lines := input_line chan :: !lines done with End_of_file -> ()); let lines = List.rev !lines in let stat = Unix.close_process_in chan in - (match stat with - | Unix.WEXITED 0 -> () + match stat with + | Unix.WEXITED 0 -> + (* Command exited correctly, return its output *) + lines + | Unix.WEXITED i when ignore_error -> + (* Command failed. in case such as 'ls something*' when path doesn't exist + * and desired behavior is to get empty list instead of error. + * This is useful for probing partial downloads *) + [] | Unix.WEXITED i -> error ~prog (f_"external command '%s' exited with error %d") cmd i | Unix.WSIGNALED i -> error ~prog (f_"external command '%s' killed by signal %d") cmd i | Unix.WSTOPPED i -> error ~prog (f_"external command '%s' stopped by signal %d") cmd i - ); - lines (* Run uuidgen to return a random UUID. *) let uuidgen ~prog () = diff --git a/mllib/common_utils.mli b/mllib/common_utils.mli index 28ba648..ce2242a 100644 --- a/mllib/common_utils.mli +++ b/mllib/common_utils.mli @@ -109,7 +109,7 @@ val compare_version : string -> string -> int val compare_lvm2_uuids : string -> string -> int (** Compare two LVM2 UUIDs, ignoring '-' characters. *) -val external_command : prog:string -> string -> string list +val external_command : prog:string -> ?ignore_error:bool -> string -> string list (** Run an external command, slurp up the output as a list of lines. *) val uuidgen : prog:string -> unit -> string -- 1.9.3