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https://github.com/fish-shell/fish-shell
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65 lines
2.1 KiB
Fish
65 lines
2.1 KiB
Fish
function eval -S -d "Evaluate parameters as a command"
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# keep a copy of the previous $status and use restore_status
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# to preserve the status in case the block that is evaluated
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# does not modify the status itself.
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set -l status_copy $status
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function __fish_restore_status
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return $argv[1]
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end
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if not set -q argv[2]
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# like most builtins, we only check for -h/--help
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# if we only have a single argument
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switch "$argv[1]"
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case -h --help
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__fish_print_help eval
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return 0
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end
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end
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# If we are in an interactive shell, eval should enable full
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# job control since it should behave like the real code was
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# executed. If we don't do this, commands that expect to be
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# used interactively, like less, wont work using eval.
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set -l mode
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if status --is-interactive-job-control
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set mode interactive
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else
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if status --is-full-job-control
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set mode full
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else
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set mode none
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end
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end
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if status --is-interactive
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status --job-control full
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end
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__fish_restore_status $status_copy
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# To eval 'foo', we construct a block "begin ; foo; end <&3 3<&-"
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# Note the redirections are also within the quotes.
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#
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# We then pipe this to 'source 3<&0’.
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#
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# You might expect that the dup2(3, stdin) should overwrite stdin,
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# and therefore prevent 'source' from reading the piped-in block. This doesn't happen
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# because when you pipe to a builtin, we don't overwrite stdin with the read end
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# of the block; instead we set a separate fd in a variable 'builtin_stdin', which is
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# what it reads from. So builtins are magic in that, in pipes, their stdin
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# is not fd 0.
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#
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# ‘source’ does not apply the redirections to itself. Instead it saves them and passes
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# them as block-level redirections to parser.eval(). Ultimately the eval’d code sees
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# the following redirections (in the following order):
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# dup2 0 -> 3
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# dup2 pipe -> 0
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# dup2 3 -> 0
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# where the pipe is the pipe we get from piping ‘echo’ to ‘source’. Thus the redirection
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# effectively makes stdin fd0, instead of the thing that was piped to ‘source’
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echo "begin; $argv "\n" ;end <&3 3<&-" | source 3<&0
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set -l res $status
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status --job-control $mode
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return $res
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end
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