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