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author | 2015-01-07 14:56:41 -0800 | |
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committer | 2015-01-07 14:56:41 -0800 | |
commit | 906d23560126c02d4b489c305112d443a85813b3 (patch) | |
tree | 786deb321424fa464d300cf285464ec14cfd88af /share/functions/eval.fish | |
parent | e045eabad63e40684fcb335247ed6cfe0ec5493a (diff) |
Add more expository comments to eval, and remove a useless parameter
Diffstat (limited to 'share/functions/eval.fish')
-rw-r--r-- | share/functions/eval.fish | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/share/functions/eval.fish b/share/functions/eval.fish index 15455402..382e6fc8 100644 --- a/share/functions/eval.fish +++ b/share/functions/eval.fish @@ -29,10 +29,9 @@ function eval -S -d "Evaluate parameters as a command" end # 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. + # 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 @@ -40,8 +39,17 @@ function eval -S -d "Evaluate parameters as a command" # 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 eval2_inner <&3 3<&-" | source 3<&0 + echo "begin; $argv "\n" ;end <&3 3<&-" | source 3<&0 set -l res $status status --job-control $mode |