diff options
Diffstat (limited to 'share/functions/eval.fish')
| -rw-r--r-- | share/functions/eval.fish | 53 |
1 files changed, 39 insertions, 14 deletions
diff --git a/share/functions/eval.fish b/share/functions/eval.fish index 939b17c9..052d4171 100644 --- a/share/functions/eval.fish +++ b/share/functions/eval.fish @@ -1,4 +1,21 @@ function eval -S -d "Evaluate parameters as a command" + # keep a copy of the previous $status and use restore_status + # to preserve the status in case the block that is evaluated + # does not modify the status itself. + set -l status_copy $status + function __fish_restore_status + return $argv[1] + end + + if not set -q argv[2] + # like most builtins, we only check for -h/--help + # if we only have a single argument + switch "$argv[1]" + case -h --help + __fish_print_help eval + return 0 + end + end # If we are in an interactive shell, eval should enable full # job control since it should behave like the real code was @@ -18,21 +35,29 @@ function eval -S -d "Evaluate parameters as a command" if status --is-interactive status --job-control full end + __fish_restore_status $status_copy - # rfish: To eval 'foo', we construct a block "begin ; foo; end <&3 3<&-" - # The 'eval2_inner' is a param to 'begin' itself; I believe it does nothing. - # Note the redirections are also within the quotes. - # - # We then pipe this to 'source 3<&0' which dup2's 3 to stdin. - # - # You might expect that the dup2(3, stdin) should overwrite stdin, - # and therefore prevent 'source' from reading the piped-in block. This doesn't happen - # because when you pipe to a builtin, we don't overwrite stdin with the read end - # of the block; instead we set a separate fd in a variable 'builtin_stdin', which is - # what it reads from. So builtins are magic in that, in pipes, their stdin - # is not fd 0. - - echo "begin; $argv "\n" ;end eval2_inner <&3 3<&-" | source 3<&0 + # To eval 'foo', we construct a block "begin ; foo; end <&3 3<&-" + # Note the redirections are also within the quotes. + # + # We then pipe this to 'source 3<&0’. + # + # You might expect that the dup2(3, stdin) should overwrite stdin, + # and therefore prevent 'source' from reading the piped-in block. This doesn't happen + # because when you pipe to a builtin, we don't overwrite stdin with the read end + # of the block; instead we set a separate fd in a variable 'builtin_stdin', which is + # what it reads from. So builtins are magic in that, in pipes, their stdin + # is not fd 0. + # + # ‘source’ does not apply the redirections to itself. Instead it saves them and passes + # them as block-level redirections to parser.eval(). Ultimately the eval’d code sees + # the following redirections (in the following order): + # dup2 0 -> 3 + # dup2 pipe -> 0 + # dup2 3 -> 0 + # where the pipe is the pipe we get from piping ‘echo’ to ‘source’. Thus the redirection + # effectively makes stdin fd0, instead of the thing that was piped to ‘source’ + echo "begin; $argv "\n" ;end <&3 3<&-" | source 3<&0 set -l res $status status --job-control $mode |