1 | 2008-07-14
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2 |
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3 | Command parsing
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4 |
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5 | Command parsing results in a list of "pipe" structures.
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6 | This list correspond not only to usual "pipe1 || pipe2 && pipe3"
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7 | lists, but it also controls execution of if, while, etc statements.
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8 | Every such statement is a list for hush. List consists of pipes.
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9 |
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10 | struct pipe fields:
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11 | smallint res_word - "none" for normal commands,
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12 | "if" for if condition etc
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13 | struct child_prog progs[] - array of commands in pipe
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14 | smallint followup - how this pipe is related to next: is it
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15 | "pipe; pipe", "pipe & pipe" "pipe && pipe",
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16 | "pipe || pipe"?
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17 |
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18 | Blocks of commands { pipe; pipe; } and (pipe; pipe) are represented
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19 | as one pipe struct with one progs[0] element which is a "group" -
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20 | struct child_prog can contain a list of pipes. Sometimes these
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21 | "groups" are created implicitly, e.g. every control
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22 | statement (if, while, etc) sits inside its own group.
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23 |
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24 | res_word controls statement execution. Examples:
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25 |
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26 | "echo Hello" -
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27 | pipe 0 res_word=NONE followup=SEQ prog[0] 'echo' 'Hello'
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28 | pipe 1 res_word=NONE followup=SEQ
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29 |
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30 | "echo foo || echo bar" -
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31 | pipe 0 res_word=NONE followup=OR prog[0] 'echo' 'foo'
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32 | pipe 1 res_word=NONE followup=SEQ prog[0] 'echo' 'bar'
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33 | pipe 2 res_word=NONE followup=SEQ
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34 |
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35 | "if true; then echo Hello; true; fi" -
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36 | res_word=NONE followup=SEQ
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37 | prog 0 group {}:
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38 | pipe 0 res_word=IF followup=SEQ prog[0] 'true'
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39 | pipe 1 res_word=THEN followup=SEQ prog[0] 'echo' 'Hello'
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40 | pipe 2 res_word=THEN followup=SEQ prog[0] 'true'
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41 | pipe 3 res_word=FI followup=SEQ
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42 | pipe 4 res_word=NONE followup=(null)
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43 | pipe 1 res_word=NONE followup=SEQ
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44 |
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45 | Above you see that if is a list, and it sits in a {} group
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46 | implicitly created by hush. Also note two THEN res_word's -
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47 | it is explained below.
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48 |
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49 | "if true; then { echo Hello; true; }; fi" -
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50 | pipe 0 res_word=NONE followup=SEQ
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51 | prog 0 group {}:
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52 | pipe 0 res_word=IF followup=SEQ prog[0] 'true'
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53 | pipe 1 res_word=THEN followup=SEQ
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54 | prog 0 group {}:
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55 | pipe 0 res_word=NONE followup=SEQ prog[0] 'echo' 'Hello'
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56 | pipe 1 res_word=NONE followup=SEQ prog[0] 'true'
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57 | pipe 2 res_word=NONE followup=SEQ
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58 | pipe 2 res_word=NONE followup=(null)
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59 | pipe 1 res_word=NONE followup=SEQ
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60 |
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61 | "for v in a b; do echo $v; true; done" -
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62 | pipe 0 res_word=NONE followup=SEQ
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63 | prog 0 group {}:
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64 | pipe 0 res_word=FOR followup=SEQ prog[0] 'v'
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65 | pipe 1 res_word=IN followup=SEQ prog[0] 'a' 'b'
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66 | pipe 2 res_word=DO followup=SEQ prog[0] 'echo' '$v'
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67 | pipe 3 res_word=DO followup=SEQ prog[0] 'true'
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68 | pipe 4 res_word=DONE followup=SEQ
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69 | pipe 5 res_word=NONE followup=(null)
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70 | pipe 1 res_word=NONE followup=SEQ
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71 |
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72 | Note how "THEN" and "DO" does not just mark the first pipe,
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73 | it "sticks" to all pipes in the body. This is used when
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74 | hush executes parsed pipes.
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75 |
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76 | Dummy trailing pipes with no commands are artifacts of imperfect
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77 | parsing algorithm - done_pipe() appends new pipe struct beforehand
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78 | and last one ends up empty and unused.
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79 |
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80 | "for" and "case" statements (ab)use progs[] to keep their data
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81 | instead of argv vector progs[] usually do. "for" keyword is forcing
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82 | pipe termination after first word, which makes hush see
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83 | "for v in..." as "for v; in...". "case" keyword does the same.
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84 | Other judiciuosly placed hacks make hush see
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85 | "case word in a) cmd1;; b) cmd2;; esac" as if it was
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86 | "case word; match a; cmd; match b; cmd2; esac"
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87 | ("match" is a fictitious keyword here):
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88 |
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89 | "case word in a) cmd1;; b) cmd2; esac" -
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90 | pipe 0 res_word=NONE followup=1 SEQ
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91 | prog 0 group {}:
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92 | pipe 0 res_word=CASE followup=SEQ prog[0] 'word'
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93 | pipe 1 res_word=MATCH followup=SEQ prog[0] 'a'
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94 | pipe 2 res_word=CASEI followup=SEQ prog[0] 'cmd1'
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95 | pipe 3 res_word=MATCH followup=SEQ prog[0] 'b'
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96 | pipe 4 res_word=CASEI followup=SEQ prog[0] 'cmd2'
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97 | pipe 5 res_word=CASEI followup=SEQ prog[0] 'cmd3'
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98 | pipe 6 res_word=ESAC followup=SEQ
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99 | pipe 7 res_word=NONE followup=(null)
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100 | pipe 1 res_word=NONE followup=SEQ
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101 |
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102 |
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103 | 2008-01
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104 |
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105 | Command execution
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106 |
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107 | /* callsite: process_command_subs */
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108 | generate_stream_from_list(struct pipe *head) - handles `cmds`
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109 | create UNIX pipe
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110 | [v]fork
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111 | child:
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112 | redirect pipe output to stdout
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113 | _exit(run_list(head)); /* leaks memory */
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114 | parent:
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115 | return UNIX pipe's output fd
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116 | /* head is freed by the caller */
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117 |
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118 | /* callsite: parse_and_run_stream */
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119 | run_and_free_list(struct pipe *)
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120 | run_list(struct pipe *)
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121 | free_pipe_list(struct pipe *)
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122 |
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123 | /* callsites: generate_stream_from_list, run_and_free_list, pseudo_exec, run_pipe */
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124 | run_list(struct pipe *) - handles "cmd; cmd2 && cmd3", while/for/do loops
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125 | run_pipe - for every pipe in list
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126 |
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127 | /* callsite: run_list */
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128 | run_pipe - runs "cmd1 | cmd2 | cmd3 [&]"
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129 | run_list - used if only one cmd and it is of the form "{cmds;}"
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130 | forks for every cmd if more than one cmd or if & is there
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131 | pseudo_exec - runs each "cmdN" (handles builtins etc)
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132 |
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133 | /* callsite: run_pipe */
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134 | pseudo_exec - runs "cmd" (handles builtins etc)
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135 | exec - execs external programs
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136 | run_list - used if cmdN is "(cmds)" or "{cmds;}"
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137 | /* problem: putenv's malloced strings into environ -
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138 | ** with vfork they will leak into parent process
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139 | */
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140 | /* problem with ENABLE_FEATURE_SH_STANDALONE:
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141 | ** run_applet_no_and_exit(a, argv) uses exit - this can interfere
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142 | ** with vfork - switch to _exit there?
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143 | */
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