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139 lines
4.9 KiB
Plaintext
139 lines
4.9 KiB
Plaintext
2008-07-14
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Command parsing
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Command parsing results in "pipe" structures. "Pipe" structure
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does not always correspond to what sh language calls "pipe",
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it also controls execution of if, while, etc statements.
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struct pipe fields:
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smallint res_word - "none" for normal commands,
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"if" for if condition etc
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struct child_prog progs[] - array of commands in pipe
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smallint followup - how this pipe is related to next: is it
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"pipe; pipe", "pipe & pipe" "pipe && pipe",
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"pipe || pipe"?
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Blocks of commands { pipe; pipe; } and (pipe; pipe) are represented
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as one pipe struct with one progs[0] element which is a "group" -
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struct child_prog can contain a list of pipes. Sometimes these
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"groups" are created implicitly, e.g. every control
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statement (if, while, etc) sits inside its own "pipe" struct).
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res_word controls statement execution. Examples:
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"echo Hello" -
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pipe 0 res_word=NONE followup=SEQ prog[0] 'echo' 'Hello'
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pipe 1 res_word=NONE followup=1 SEQ
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"echo foo || echo bar" -
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pipe 0 res_word=NONE followup=OR prog[0] 'echo' 'foo'
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pipe 1 res_word=NONE followup=SEQ prog[0] 'echo' 'bar'
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pipe 2 res_word=NONE followup=SEQ
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"if true; then echo Hello; true; fi" -
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res_word=NONE followup=SEQ
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prog 0 group {}:
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pipe 0 res_word=IF followup=SEQ prog[0] 'true'
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pipe 1 res_word=THEN followup=SEQ prog[0] 'echo' 'Hello'
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pipe 2 res_word=THEN followup=SEQ prog[0] 'true'
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pipe 3 res_word=FI followup=SEQ
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pipe 4 res_word=NONE followup=(null)
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pipe 1 res_word=NONE followup=SEQ
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"if true; then { echo Hello; true; }; fi" -
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pipe 0 res_word=NONE followup=SEQ
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prog 0 group {}:
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pipe 0 res_word=IF followup=SEQ prog[0] 'true'
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pipe 1 res_word=THEN followup=SEQ
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prog 0 group {}:
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pipe 0 res_word=NONE followup=SEQ prog[0] 'echo' 'Hello'
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pipe 1 res_word=NONE followup=SEQ prog[0] 'true'
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pipe 2 res_word=NONE followup=SEQ
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pipe 2 res_word=NONE followup=(null)
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pipe 1 res_word=NONE followup=1 SEQ
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"for v in a b; do echo $v; true; done" -
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pipe 0 res_word=NONE followup=SEQ
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prog 0 group {}:
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pipe 0 res_word=FOR followup=SEQ prog[0] 'v'
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pipe 1 res_word=IN followup=SEQ prog[0] 'a' 'b'
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pipe 2 res_word=DO followup=SEQ prog[0] 'echo' '$v'
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pipe 3 res_word=DO followup=SEQ prog[0] 'true'
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pipe 4 res_word=DONE followup=SEQ
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pipe 5 res_word=NONE followup=(null)
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pipe 1 res_word=NONE followup=SEQ
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Note how "THEN" and "DO" does not just mark the first pipe,
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it "sticks" to all pipes in the body. This is used when
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hush executes parsed pipes.
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Dummy trailing pipes with no commands are artifacts of imperfect
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parsing algorithm - done_pipe() appends new pipe struct beforehand
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and last one ends up empty and unused.
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"for" and "case" statements (ab)use progs[] to keep their data
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instead of argv vector progs[] usually do. "for" keyword is forcing
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pipe termination after first word, which makes hush see
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"for v in..." as "for v; in...". "case" keyword does the same.
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Other judiciuosly placed hacks make hush see
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"case word in a) cmd1;; b) cmd2;; esac" as if it was
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"case word; match a; cmd; match b; cmd2; esac"
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("match" is a fictitious keyword here):
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"case word in a) cmd1;; b) cmd2; esac" -
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pipe 0 res_word=NONE followup=1 SEQ
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prog 0 group {}:
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pipe 0 res_word=CASE followup=SEQ prog[0] 'word'
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pipe 1 res_word=MATCH followup=SEQ prog[0] 'a'
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pipe 2 res_word=CASEI followup=SEQ prog[0] 'cmd1'
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pipe 3 res_word=MATCH followup=SEQ prog[0] 'b'
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pipe 4 res_word=CASEI followup=SEQ prog[0] 'cmd2'
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pipe 5 res_word=CASEI followup=SEQ prog[0] 'cmd3'
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pipe 6 res_word=ESAC followup=SEQ
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pipe 7 res_word=NONE followup=(null)
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pipe 1 res_word=NONE followup=1 SEQ
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2008-01
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Command execution
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/* callsite: process_command_subs */
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generate_stream_from_list(struct pipe *head) - handles `cmds`
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create UNIX pipe
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[v]fork
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child:
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redirect pipe output to stdout
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_exit(run_list(head)); /* leaks memory */
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parent:
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return UNIX pipe's output fd
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/* head is freed by the caller */
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/* callsite: parse_and_run_stream */
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run_and_free_list(struct pipe *)
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run_list(struct pipe *)
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free_pipe_list(struct pipe *)
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/* callsites: generate_stream_from_list, run_and_free_list, pseudo_exec, run_pipe */
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run_list(struct pipe *) - handles "cmd; cmd2 && cmd3", while/for/do loops
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run_pipe - for every pipe in list
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/* callsite: run_list */
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run_pipe - runs "cmd1 | cmd2 | cmd3 [&]"
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run_list - used if only one cmd and it is of the form "{cmds;}"
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forks for every cmd if more than one cmd or if & is there
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pseudo_exec - runs each "cmdN" (handles builtins etc)
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/* callsite: run_pipe */
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pseudo_exec - runs "cmd" (handles builtins etc)
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exec - execs external programs
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run_list - used if cmdN is "(cmds)" or "{cmds;}"
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/* problem: putenv's malloced strings into environ -
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** with vfork they will leak into parent process
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*/
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/* problem with ENABLE_FEATURE_SH_STANDALONE:
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** run_applet_no_and_exit(a, argv) uses exit - this can interfere
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** with vfork - switch to _exit there?
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*/
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