1 // Copyright (c) 2008, Google Inc. 2 // All rights reserved. 3 // 4 // Redistribution and use in source and binary forms, with or without 5 // modification, are permitted provided that the following conditions are 6 // met: 7 // 8 // * Redistributions of source code must retain the above copyright 9 // notice, this list of conditions and the following disclaimer. 10 // * Redistributions in binary form must reproduce the above 11 // copyright notice, this list of conditions and the following disclaimer 12 // in the documentation and/or other materials provided with the 13 // distribution. 14 // * Neither the name of Google Inc. nor the names of its 15 // contributors may be used to endorse or promote products derived from 16 // this software without specific prior written permission. 17 // 18 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 19 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 20 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 21 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 22 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 23 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 24 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 25 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 26 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 27 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 28 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29 // 30 // --- 31 // Author: Dave Nicponski 32 // 33 // Implement helpful bash-style command line flag completions 34 // 35 // ** Functional API: 36 // HandleCommandLineCompletions() should be called early during 37 // program startup, but after command line flag code has been 38 // initialized, such as the beginning of HandleCommandLineHelpFlags(). 39 // It checks the value of the flag --tab_completion_word. If this 40 // flag is empty, nothing happens here. If it contains a string, 41 // however, then HandleCommandLineCompletions() will hijack the 42 // process, attempting to identify the intention behind this 43 // completion. Regardless of the outcome of this deduction, the 44 // process will be terminated, similar to --helpshort flag 45 // handling. 46 // 47 // ** Overview of Bash completions: 48 // Bash can be told to programatically determine completions for the 49 // current 'cursor word'. It does this by (in this case) invoking a 50 // command with some additional arguments identifying the command 51 // being executed, the word being completed, and the previous word 52 // (if any). Bash then expects a sequence of output lines to be 53 // printed to stdout. If these lines all contain a common prefix 54 // longer than the cursor word, bash will replace the cursor word 55 // with that common prefix, and display nothing. If there isn't such 56 // a common prefix, bash will display the lines in pages using 'more'. 57 // 58 // ** Strategy taken for command line completions: 59 // If we can deduce either the exact flag intended, or a common flag 60 // prefix, we'll output exactly that. Otherwise, if information 61 // must be displayed to the user, we'll take the opportunity to add 62 // some helpful information beyond just the flag name (specifically, 63 // we'll include the default flag value and as much of the flag's 64 // description as can fit on a single terminal line width, as specified 65 // by the flag --tab_completion_columns). Furthermore, we'll try to 66 // make bash order the output such that the most useful or relevent 67 // flags are the most likely to be shown at the top. 68 // 69 // ** Additional features: 70 // To assist in finding that one really useful flag, substring matching 71 // was implemented. Before pressing a <TAB> to get completion for the 72 // current word, you can append one or more '?' to the flag to do 73 // substring matching. Here's the semantics: 74 // --foo<TAB> Show me all flags with names prefixed by 'foo' 75 // --foo?<TAB> Show me all flags with 'foo' somewhere in the name 76 // --foo??<TAB> Same as prior case, but also search in module 77 // definition path for 'foo' 78 // --foo???<TAB> Same as prior case, but also search in flag 79 // descriptions for 'foo' 80 // Finally, we'll trim the output to a relatively small number of 81 // flags to keep bash quiet about the verbosity of output. If one 82 // really wanted to see all possible matches, appending a '+' to the 83 // search word will force the exhaustive list of matches to be printed. 84 // 85 // ** How to have bash accept completions from a binary: 86 // Bash requires that it be informed about each command that programmatic 87 // completion should be enabled for. Example addition to a .bashrc 88 // file would be (your path to gflags_completions.sh file may differ): 89 90 /* 91 $ complete -o bashdefault -o default -o nospace -C \ 92 '/usr/local/bin/gflags_completions.sh --tab_completion_columns $COLUMNS' \ 93 time env binary_name another_binary [...] 94 */ 95 96 // This would allow the following to work: 97 // $ /path/to/binary_name --vmodule<TAB> 98 // Or: 99 // $ ./bin/path/another_binary --gfs_u<TAB> 100 // (etc) 101 // 102 // Sadly, it appears that bash gives no easy way to force this behavior for 103 // all commands. That's where the "time" in the above example comes in. 104 // If you haven't specifically added a command to the list of completion 105 // supported commands, you can still get completions by prefixing the 106 // entire command with "env". 107 // $ env /some/brand/new/binary --vmod<TAB> 108 // Assuming that "binary" is a newly compiled binary, this should still 109 // produce the expected completion output. 110 111 112 #ifndef GOOGLE_GFLAGS_COMPLETIONS_H_ 113 #define GOOGLE_GFLAGS_COMPLETIONS_H_ 114 115 namespace google { 116 117 void HandleCommandLineCompletions(void); 118 119 } 120 121 #endif // GOOGLE_GFLAGS_COMPLETIONS_H_ 122