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1 @c Copyright (C) 1996, 1997 John W. Eaton |
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2 @c This is part of the Octave manual. |
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3 @c For copying conditions, see the file gpl.texi. |
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4 |
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5 @node Getting Started |
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6 @chapter Getting Started |
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7 |
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8 This chapter explains some of Octave's basic features, including how to |
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9 start an Octave session, get help at the command prompt, edit the |
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10 command line, and write Octave programs that can be executed as commands |
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11 from your shell. |
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12 |
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13 @menu |
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14 * Invoking Octave:: |
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15 * Quitting Octave:: |
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16 * Getting Help:: |
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17 * Command Line Editing:: |
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18 * Errors:: |
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19 * Executable Octave Programs:: |
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20 * Comments:: |
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21 @end menu |
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22 |
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23 @node Invoking Octave |
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24 @section Invoking Octave |
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25 |
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26 Normally, Octave is used interactively by running the program |
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27 @samp{octave} without any arguments. Once started, Octave reads |
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28 commands from the terminal until you tell it to exit. |
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29 |
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30 You can also specify the name of a file on the command line, and Octave |
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31 will read and execute the commands from the named file and then exit |
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32 when it is finished. |
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33 |
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34 You can further control how Octave starts by using the command-line |
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35 options described in the next section, and Octave itself can remind you |
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36 of the options available. Type @samp{octave --help} to display all |
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37 available options and briefly describe their use (@samp{octave -h} is a |
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38 shorter equivalent). |
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39 |
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40 @menu |
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41 * Command Line Options:: |
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42 * Startup Files:: |
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43 @end menu |
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44 |
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45 @node Command Line Options |
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46 @subsection Command Line Options |
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47 @cindex Octave command options |
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48 @cindex command options |
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49 @cindex options, Octave command |
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50 |
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51 Here is a complete list of all the command line options that Octave |
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52 accepts. |
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53 |
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54 @table @code |
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55 @item --debug |
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56 @itemx -d |
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57 @cindex @code{--debug} |
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58 @cindex @code{-d} |
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59 Enter parser debugging mode. Using this option will cause Octave's |
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60 parser to print a lot of information about the commands it reads, and is |
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61 probably only useful if you are actually trying to debug the parser. |
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62 |
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63 @item --echo-commands |
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64 @itemx -x |
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65 @cindex @code{--echo-commands} |
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66 @cindex @code{-x} |
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67 Echo commands as they are executed. |
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68 |
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69 @item --eval @var{code} |
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70 Evaluate @var{code} and exit when done unless @code{--persist} is also |
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71 specified. |
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72 |
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73 @item --exec-path @var{path} |
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74 @cindex @code{--exec-path @var{path}} |
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75 Specify the path to search for programs to run. The value of @var{path} |
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76 specified on the command line will override any value of |
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77 @code{OCTAVE_EXEC_PATH} found in the environment, but not any commands |
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78 in the system or user startup files that set the built-in variable |
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79 @code{EXEC_PATH}. |
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80 |
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81 @item --help |
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82 @itemx -h |
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83 @itemx -? |
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84 @cindex @code{--help} |
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85 @cindex @code{-h} |
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86 @cindex @code{-?} |
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87 Print short help message and exit. |
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88 |
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89 @item --info-file @var{filename} |
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90 @cindex @code{--info-file @var{filename}} |
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91 Specify the name of the info file to use. The value of @var{filename} |
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92 specified on the command line will override any value of |
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93 @code{OCTAVE_INFO_FILE} found in the environment, but not any commands |
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94 in the system or user startup files that use the the @code{info_file} |
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95 function. |
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96 |
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97 @item --info-program @var{program} |
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98 @cindex @code{--info-program @var{program}} |
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99 Specify the name of the info program to use. The value of @var{program} |
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100 specified on the command line will override any value of |
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101 @code{OCTAVE_INFO_PROGRAM} found in the environment, but not any |
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102 commands in the system or user startup files that use the |
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103 @code{info_program} function. |
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104 |
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105 @item --interactive |
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106 @itemx -i |
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107 @cindex @code{--interactive} |
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108 @cindex @code{-i} |
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109 Force interactive behavior. This can be useful for running Octave via a |
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110 remote shell command or inside an Emacs shell buffer. For another way |
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111 to run Octave within Emacs, see @ref{Emacs}. |
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112 |
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113 @item --no-history |
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114 @itemx -H |
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115 Disable command-line history. |
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116 |
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117 @item --no-init-file |
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118 @cindex @code{--no-init-file} |
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119 Don't read the @file{~/.octaverc} or @file{.octaverc} files. |
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120 |
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121 @item --no-line-editing |
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122 @cindex @code{--no-line-editing} |
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123 Disable command-line editing. |
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124 |
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125 @item --no-site-file |
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126 @cindex @code{--no-site-file} |
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127 Don't read the site-wide @file{octaverc} file. |
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128 |
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129 @item --norc |
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130 @itemx -f |
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131 @cindex @code{--norc} |
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132 @cindex @code{-f} |
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133 Don't read any of the system or user initialization files at startup. |
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134 This is equivalent to using both of the options @code{--no-init-file} |
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135 and @code{--no-site-file}. |
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136 |
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137 @item --path @var{path} |
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138 @itemx -p @var{path} |
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139 @cindex @code{--path @var{path}} |
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140 @cindex @code{-p @var{path}} |
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141 Specify the path to search for function files. The value of @var{path} |
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142 specified on the command line will override any value of |
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143 @code{OCTAVE_PATH} found in the environment, but not any commands in the |
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144 system or user startup files that set the internal variable @code{LOADPATH} |
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145 through one of the path functions. |
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146 |
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147 @item --persist |
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148 Go to interactive mode after @code{--eval} or reading from a file |
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149 named on the command line. |
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150 |
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151 @item --silent |
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152 @itemx --quiet |
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153 @itemx -q |
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154 @cindex @code{--silent} |
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155 @cindex @code{--quiet} |
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156 @cindex @code{-q} |
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157 Don't print the usual greeting and version message at startup. |
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158 |
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159 @item --traditional |
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160 @itemx --braindead |
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161 @cindex @code{--traditional} |
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162 @cindex @code{--braindead} |
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163 Set initial values for user-preference variables to the following |
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164 values for compatibility with @sc{Matlab}. |
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165 |
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166 @example |
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167 @group |
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168 PS1 = ">> " |
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169 PS2 = "" |
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170 beep_on_error = true |
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171 crash_dumps_octave_core = false |
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172 default_save_options = "-mat-binary" |
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173 fixed_point_format = true |
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174 page_screen_output = false |
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175 print_empty_dimensions = false |
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176 @end group |
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177 @end example |
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178 |
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179 @item --verbose |
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180 @itemx -V |
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181 @cindex @code{--verbose} |
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182 @cindex @code{-V} |
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183 Turn on verbose output. |
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184 |
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185 @item --version |
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186 @itemx -v |
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187 @cindex @code{--version} |
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188 @cindex @code{-v} |
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189 Print the program version number and exit. |
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190 |
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191 @item @var{file} |
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192 Execute commands from @var{file}. Exit when done unless |
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193 @code{--persist} is also specified. |
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194 @end table |
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195 |
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196 Octave also includes several built-in variables that contain information |
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197 about the command line, including the number of arguments and all of the |
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198 options. |
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199 |
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200 @DOCSTRING(argv) |
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201 |
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202 @DOCSTRING(program_invocation_name) |
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203 |
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204 Here is an example of using these functions to reproduce Octave's |
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205 command line. |
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206 |
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207 @example |
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208 printf ("%s", program_name ()); |
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209 for i = 1:nargin |
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210 arg_list = argv (); |
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211 printf (" %s", arg_list@{i@}); |
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212 endfor |
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213 printf ("\n"); |
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214 @end example |
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215 |
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216 @noindent |
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217 @xref{Index Expressions}, for an explanation of how to properly index |
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218 arrays of strings and substrings in Octave, and @xref{Defining Functions}, |
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219 for information about the variable @code{nargin}. |
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220 |
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221 @node Startup Files |
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222 @subsection Startup Files |
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223 @cindex initialization |
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224 @cindex startup |
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225 |
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226 When Octave starts, it looks for commands to execute from the following |
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227 files: |
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228 |
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229 @cindex startup files |
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230 |
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231 @table @code |
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232 @item @var{octave-home}/share/octave/site/m/startup/octaverc |
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233 Where @var{octave-home} is the directory in which all of Octave is |
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234 installed (the default is @file{@value{OCTAVEHOME}}). This file is |
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235 provided so that changes to the default Octave environment can be made |
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236 globally for all users at your site for all versions of Octave you have |
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237 installed. Some care should be taken when making changes to this file, |
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238 since all users of Octave at your site will be affected. |
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239 |
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240 @item @var{octave-home}/share/octave/@var{version}/m/startup/octaverc |
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241 Where @var{octave-home} is the directory in which all of Octave is |
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242 installed (the default is @file{@value{OCTAVEHOME}}), and @var{version} |
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243 is the version number of Octave. This file is provided so that changes |
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244 to the default Octave environment can be made globally for all users for |
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245 a particular version of Octave. Some care should be taken when making |
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246 changes to this file, since all users of Octave at your site will be |
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247 affected. |
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248 |
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249 @item ~/.octaverc |
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250 @cindex @code{~/.octaverc} |
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251 This file is normally used to make personal changes to the default |
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252 Octave environment. |
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253 |
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254 @item .octaverc |
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255 @cindex @code{.octaverc} |
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256 This file can be used to make changes to the default Octave environment |
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257 for a particular project. Octave searches for this file in the current |
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258 directory after it reads @file{~/.octaverc}. Any use of the @code{cd} |
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259 command in the @file{~/.octaverc} file will affect the directory that |
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260 Octave searches for the file @file{.octaverc}. |
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261 |
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262 If you start Octave in your home directory, commands from from the file |
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263 @file{~/.octaverc} will only be executed once. |
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264 @end table |
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265 |
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266 A message will be displayed as each of the startup files is read if you |
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267 invoke Octave with the @code{--verbose} option but without the |
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268 @code{--silent} option. |
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269 |
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270 Startup files may contain any valid Octave commands, including function |
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271 definitions. |
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272 |
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273 @node Quitting Octave |
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274 @section Quitting Octave |
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275 @cindex exiting octave |
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276 @cindex quitting octave |
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277 |
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278 @DOCSTRING(quit) |
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279 |
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280 @DOCSTRING(atexit) |
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281 |
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282 @node Getting Help |
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283 @section Commands for Getting Help |
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284 @cindex on-line help |
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285 @cindex help, on-line |
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286 |
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287 The entire text of this manual is available from the Octave prompt |
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288 via the command @kbd{help -i}. In addition, the documentation for |
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289 individual user-written functions and variables is also available via |
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290 the @kbd{help} command. This section describes the commands used for |
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291 reading the manual and the documentation strings for user-supplied |
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292 functions and variables. @xref{Function Files}, for more information |
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293 about how to document the functions you write. |
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294 |
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295 @DOCSTRING(help) |
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296 |
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297 The help command can give you information about operators, but not the |
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298 comma and semicolons that are used as command separators. To get help |
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299 for those, you must type @kbd{help comma} or @kbd{help semicolon}. |
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300 |
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301 @DOCSTRING(info_file) |
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302 |
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303 @DOCSTRING(info_program) |
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304 |
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305 @DOCSTRING(makeinfo_program) |
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306 |
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307 @DOCSTRING(suppress_verbose_help_message) |
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308 |
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309 @node Command Line Editing |
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310 @section Command Line Editing |
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311 @cindex command-line editing |
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312 @cindex editing the command line |
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313 |
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314 Octave uses the GNU readline library to provide an extensive set of |
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315 command-line editing and history features. Only the most common |
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316 features are described in this manual. Please see The GNU Readline |
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317 Library manual for more information. |
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318 |
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319 To insert printing characters (letters, digits, symbols, etc.), simply |
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320 type the character. Octave will insert the character at the cursor and |
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321 advance the cursor forward. |
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322 |
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323 Many of the command-line editing functions operate using control |
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324 characters. For example, the character @kbd{Control-a} moves the cursor |
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325 to the beginning of the line. To type @kbd{C-a}, hold down @key{CTRL} |
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326 and then press @key{a}. In the following sections, control characters |
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327 such as @kbd{Control-a} are written as @kbd{C-a}. |
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328 |
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329 Another set of command-line editing functions use Meta characters. On |
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330 some terminals, you type @kbd{M-u} by holding down @key{META} and |
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331 pressing @key{u}. If your terminal does not have a @key{META} key, you |
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332 can still type Meta charcters using two-character sequences starting |
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333 with @kbd{ESC}. Thus, to enter @kbd{M-u}, you could type |
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334 @key{ESC}@key{u}. The @kbd{ESC} character sequences are also allowed on |
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335 terminals with real Meta keys. In the following sections, Meta |
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336 characters such as @kbd{Meta-u} are written as @kbd{M-u}. |
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337 |
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338 |
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339 @menu |
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340 * Cursor Motion:: |
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341 * Killing and Yanking:: |
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342 * Commands For Text:: |
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343 * Commands For Completion:: |
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344 * Commands For History:: |
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345 * Customizing readline:: |
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346 * Customizing the Prompt:: |
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347 * Diary and Echo Commands:: |
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348 @end menu |
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349 |
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350 @node Cursor Motion |
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351 @subsection Cursor Motion |
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352 |
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353 The following commands allow you to position the cursor. |
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354 |
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355 @table @kbd |
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356 @item C-b |
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357 Move back one character. |
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358 |
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359 @item C-f |
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360 Move forward one character. |
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361 |
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362 @item @key{DEL} |
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363 Delete the character to the left of the cursor. |
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364 |
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365 @item C-d |
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366 Delete the character underneath the cursor. |
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367 |
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368 @item M-f |
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369 Move forward a word. |
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370 |
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371 @item M-b |
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372 Move backward a word. |
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373 |
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374 @item C-a |
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375 Move to the start of the line. |
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376 |
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377 @item C-e |
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378 Move to the end of the line. |
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379 |
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380 @item C-l |
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381 Clear the screen, reprinting the current line at the top. |
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382 |
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383 @item C-_ |
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384 @itemx C-/ |
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385 Undo the last thing that you did. You can undo all the way back to an |
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386 empty line. |
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387 |
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388 @item M-r |
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389 Undo all changes made to this line. This is like typing the `undo' |
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390 command enough times to get back to the beginning. |
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391 @end table |
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392 |
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393 The above table describes the most basic possible keystrokes that you need |
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394 in order to do editing of the input line. On most terminals, you can |
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395 also use the arrow keys in place of @kbd{C-f} and @kbd{C-b} to move |
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396 forward and backward. |
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397 |
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398 Notice how @kbd{C-f} moves forward a character, while @kbd{M-f} moves |
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399 forward a word. It is a loose convention that control keystrokes |
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400 operate on characters while meta keystrokes operate on words. |
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401 |
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402 There is also a function available so that you can clear the screen from |
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403 within Octave programs. |
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404 |
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405 @cindex clearing the screen |
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406 |
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407 @DOCSTRING(clc) |
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408 |
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409 @node Killing and Yanking |
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410 @subsection Killing and Yanking |
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411 |
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412 @dfn{Killing} text means to delete the text from the line, but to save |
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413 it away for later use, usually by @dfn{yanking} it back into the line. |
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414 If the description for a command says that it `kills' text, then you can |
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415 be sure that you can get the text back in a different (or the same) |
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416 place later. |
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417 |
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418 Here is the list of commands for killing text. |
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419 |
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420 @table @kbd |
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421 @item C-k |
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422 Kill the text from the current cursor position to the end of the line. |
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423 |
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424 @item M-d |
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425 Kill from the cursor to the end of the current word, or if between |
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426 words, to the end of the next word. |
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427 |
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428 @item M-@key{DEL} |
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429 Kill from the cursor to the start of the previous word, or if between |
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430 words, to the start of the previous word. |
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431 |
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432 @item C-w |
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433 Kill from the cursor to the previous whitespace. This is different than |
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434 @kbd{M-@key{DEL}} because the word boundaries differ. |
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435 @end table |
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436 |
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437 And, here is how to @dfn{yank} the text back into the line. Yanking |
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438 means to copy the most-recently-killed text from the kill buffer. |
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439 |
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440 @table @kbd |
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441 @item C-y |
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442 Yank the most recently killed text back into the buffer at the cursor. |
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443 |
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|
444 @item M-y |
|
|
445 Rotate the kill-ring, and yank the new top. You can only do this if |
|
|
446 the prior command is @kbd{C-y} or @kbd{M-y}. |
|
|
447 @end table |
|
|
448 |
|
|
449 When you use a kill command, the text is saved in a @dfn{kill-ring}. |
|
|
450 Any number of consecutive kills save all of the killed text together, so |
|
|
451 that when you yank it back, you get it in one clean sweep. The kill |
|
|
452 ring is not line specific; the text that you killed on a previously |
|
|
453 typed line is available to be yanked back later, when you are typing |
|
|
454 another line. |
|
|
455 |
|
4167
|
456 @node Commands For Text |
|
3294
|
457 @subsection Commands For Changing Text |
|
|
458 |
|
|
459 The following commands can be used for entering characters that would |
|
|
460 otherwise have a special meaning (e.g., @kbd{TAB}, @kbd{C-q}, etc.), or |
|
|
461 for quickly correcting typing mistakes. |
|
|
462 |
|
|
463 @table @kbd |
|
|
464 @item C-q |
|
|
465 @itemx C-v |
|
|
466 Add the next character that you type to the line verbatim. This is |
|
|
467 how to insert things like @kbd{C-q} for example. |
|
|
468 |
|
|
469 @item M-@key{TAB} |
|
|
470 Insert a tab character. |
|
|
471 |
|
|
472 @item C-t |
|
|
473 Drag the character before the cursor forward over the character at the |
|
|
474 cursor, also moving the cursor forward. If the cursor is at the end of |
|
|
475 the line, then transpose the two characters before it. |
|
|
476 |
|
|
477 @item M-t |
|
|
478 Drag the word behind the cursor past the word in front of the cursor |
|
|
479 moving the cursor over that word as well. |
|
|
480 |
|
|
481 @item M-u |
|
|
482 Uppercase the characters following the cursor to the end of the current |
|
|
483 (or following) word, moving the cursor to the end of the word. |
|
|
484 |
|
|
485 @item M-l |
|
|
486 Lowecase the characters following the cursor to the end of the current |
|
|
487 (or following) word, moving the cursor to the end of the word. |
|
|
488 |
|
|
489 @item M-c |
|
|
490 Uppercase the character following the cursor (or the beginning of the |
|
|
491 next word if the cursor is between words), moving the cursor to the end |
|
|
492 of the word. |
|
|
493 @end table |
|
|
494 |
|
4167
|
495 @node Commands For Completion |
|
3294
|
496 @subsection Letting Readline Type For You |
|
|
497 @cindex command completion |
|
|
498 |
|
|
499 The following commands allow Octave to complete command and variable |
|
|
500 names for you. |
|
|
501 |
|
|
502 @table @kbd |
|
|
503 @item @key{TAB} |
|
|
504 Attempt to do completion on the text before the cursor. Octave can |
|
|
505 complete the names of commands and variables. |
|
|
506 |
|
|
507 @item M-? |
|
|
508 List the possible completions of the text before the cursor. |
|
|
509 @end table |
|
|
510 |
|
3332
|
511 @DOCSTRING(completion_append_char) |
|
3294
|
512 |
|
3332
|
513 @DOCSTRING(completion_matches) |
|
3294
|
514 |
|
4167
|
515 @node Commands For History |
|
3294
|
516 @subsection Commands For Manipulating The History |
|
|
517 @cindex command history |
|
|
518 @cindex input history |
|
|
519 @cindex history of commands |
|
|
520 |
|
|
521 Octave normally keeps track of the commands you type so that you can |
|
|
522 recall previous commands to edit or execute them again. When you exit |
|
|
523 Octave, the most recent commands you have typed, up to the number |
|
|
524 specified by the variable @code{history_size}, are saved in a file. |
|
|
525 When Octave starts, it loads an initial list of commands from the file |
|
|
526 named by the variable @code{history_file}. |
|
|
527 |
|
|
528 Here are the commands for simple browsing and searching the history |
|
|
529 list. |
|
|
530 |
|
|
531 @table @kbd |
|
|
532 @item @key{LFD} |
|
|
533 @itemx @key{RET} |
|
|
534 Accept the line regardless of where the cursor is. If this line is |
|
|
535 non-empty, add it to the history list. If this line was a history |
|
|
536 line, then restore the history line to its original state. |
|
|
537 |
|
|
538 @item C-p |
|
|
539 Move `up' through the history list. |
|
|
540 |
|
|
541 @item C-n |
|
|
542 Move `down' through the history list. |
|
|
543 |
|
|
544 @item M-< |
|
|
545 Move to the first line in the history. |
|
|
546 |
|
|
547 @item M-> |
|
|
548 Move to the end of the input history, i.e., the line you are entering! |
|
|
549 |
|
|
550 @item C-r |
|
|
551 Search backward starting at the current line and moving `up' through |
|
|
552 the history as necessary. This is an incremental search. |
|
|
553 |
|
|
554 @item C-s |
|
|
555 Search forward starting at the current line and moving `down' through |
|
|
556 the history as necessary. |
|
|
557 @end table |
|
|
558 |
|
|
559 On most terminals, you can also use the arrow keys in place of @kbd{C-p} |
|
|
560 and @kbd{C-n} to move through the history list. |
|
|
561 |
|
|
562 In addition to the keyboard commands for moving through the history |
|
|
563 list, Octave provides three functions for viewing, editing, and |
|
|
564 re-running chunks of commands from the history list. |
|
|
565 |
|
3332
|
566 @DOCSTRING(history) |
|
3294
|
567 |
|
3332
|
568 @DOCSTRING(edit_history) |
|
3294
|
569 |
|
3332
|
570 @DOCSTRING(run_history) |
|
3294
|
571 |
|
3368
|
572 @DOCSTRING(EDITOR) |
|
3294
|
573 |
|
3332
|
574 @DOCSTRING(history_file) |
|
3294
|
575 |
|
3332
|
576 @DOCSTRING(history_size) |
|
3294
|
577 |
|
3332
|
578 @DOCSTRING(saving_history) |
|
3294
|
579 |
|
4167
|
580 @node Customizing readline |
|
3428
|
581 @subsection Customizing @code{readline} |
|
|
582 |
|
5775
|
583 @c FIXME -- need a brief description of the ~/.inputrc file here. |
|
3428
|
584 |
|
3439
|
585 @DOCSTRING(read_readline_init_file) |
|
3428
|
586 |
|
4167
|
587 @node Customizing the Prompt |
|
3294
|
588 @subsection Customizing the Prompt |
|
|
589 @cindex prompt customization |
|
|
590 @cindex customizing the prompt |
|
|
591 |
|
|
592 The following variables are available for customizing the appearance of |
|
|
593 the command-line prompts. Octave allows the prompt to be customized by |
|
|
594 inserting a number of backslash-escaped special characters that are |
|
|
595 decoded as follows: |
|
|
596 |
|
|
597 @table @samp |
|
|
598 @item \t |
|
|
599 The time. |
|
|
600 |
|
|
601 @item \d |
|
|
602 The date. |
|
|
603 |
|
|
604 @item \n |
|
|
605 Begins a new line by printing the equivalent of a carriage return |
|
|
606 followed by a line feed. |
|
|
607 |
|
|
608 @item \s |
|
|
609 The name of the program (usually just @samp{octave}). |
|
|
610 |
|
|
611 @item \w |
|
|
612 The current working directory. |
|
|
613 |
|
|
614 @item \W |
|
|
615 The basename of the current working directory. |
|
|
616 |
|
|
617 @item \u |
|
|
618 The username of the current user. |
|
|
619 |
|
|
620 @item \h |
|
|
621 The hostname, up to the first `.'. |
|
|
622 |
|
|
623 @item \H |
|
|
624 The hostname. |
|
|
625 |
|
|
626 @item \# |
|
|
627 The command number of this command, counting from when Octave starts. |
|
|
628 |
|
|
629 @item \! |
|
|
630 The history number of this command. This differs from @samp{\#} by the |
|
|
631 number of commands in the history list when Octave starts. |
|
|
632 |
|
|
633 @item \$ |
|
|
634 If the effective UID is 0, a @samp{#}, otherwise a @samp{$}. |
|
|
635 |
|
|
636 @item \nnn |
|
|
637 The character whose character code in octal is @var{nnn}. |
|
|
638 |
|
|
639 @item \\ |
|
|
640 A backslash. |
|
|
641 @end table |
|
|
642 |
|
3332
|
643 @DOCSTRING(PS1) |
|
3294
|
644 |
|
3332
|
645 @DOCSTRING(PS2) |
|
3294
|
646 |
|
3332
|
647 @DOCSTRING(PS4) |
|
3294
|
648 |
|
4167
|
649 @node Diary and Echo Commands |
|
3294
|
650 @subsection Diary and Echo Commands |
|
|
651 @cindex diary of commands and output |
|
|
652 @cindex command and ouput logs |
|
|
653 @cindex logging commands and output |
|
|
654 @cindex echoing executing commands |
|
|
655 @cindex command echoing |
|
|
656 |
|
|
657 Octave's diary feature allows you to keep a log of all or part of an |
|
|
658 interactive session by recording the input you type and the output that |
|
|
659 Octave produces in a separate file. |
|
|
660 |
|
3332
|
661 @DOCSTRING(diary) |
|
3294
|
662 |
|
|
663 Sometimes it is useful to see the commands in a function or script as |
|
|
664 they are being evaluated. This can be especially helpful for debugging |
|
|
665 some kinds of problems. |
|
|
666 |
|
3332
|
667 @DOCSTRING(echo) |
|
3294
|
668 |
|
3332
|
669 @DOCSTRING(echo_executing_commands) |
|
3294
|
670 |
|
4167
|
671 @node Errors |
|
3294
|
672 @section How Octave Reports Errors |
|
|
673 @cindex error messages |
|
|
674 @cindex messages, error |
|
|
675 |
|
|
676 Octave reports two kinds of errors for invalid programs. |
|
|
677 |
|
|
678 A @dfn{parse error} occurs if Octave cannot understand something you |
|
|
679 have typed. For example, if you misspell a keyword, |
|
|
680 |
|
|
681 @example |
|
|
682 octave:13> functon y = f (x) y = x^2; endfunction |
|
|
683 @end example |
|
|
684 |
|
|
685 @noindent |
|
|
686 Octave will respond immediately with a message like this: |
|
|
687 |
|
|
688 @example |
|
|
689 parse error: |
|
|
690 |
|
|
691 functon y = f (x) y = x^2; endfunction |
|
|
692 ^ |
|
|
693 @end example |
|
|
694 |
|
|
695 @noindent |
|
|
696 For most parse errors, Octave uses a caret (@samp{^}) to mark the point |
|
|
697 on the line where it was unable to make sense of your input. In this |
|
|
698 case, Octave generated an error message because the keyword |
|
|
699 @code{function} was misspelled. Instead of seeing @samp{function f}, |
|
|
700 Octave saw two consecutive variable names, which is invalid in this |
|
|
701 context. It marked the error at @code{y} because the first name by |
|
|
702 itself was accepted as valid input. |
|
|
703 |
|
|
704 Another class of error message occurs at evaluation time. These |
|
|
705 errors are called @dfn{run-time errors}, or sometimes |
|
|
706 @dfn{evaluation errors} because they occur when your program is being |
|
|
707 @dfn{run}, or @dfn{evaluated}. For example, if after correcting the |
|
|
708 mistake in the previous function definition, you type |
|
|
709 |
|
|
710 @example |
|
|
711 octave:13> f () |
|
|
712 @end example |
|
|
713 |
|
|
714 @noindent |
|
|
715 Octave will respond with |
|
|
716 |
|
|
717 @example |
|
|
718 @group |
|
|
719 error: `x' undefined near line 1 column 24 |
|
|
720 error: evaluating expression near line 1, column 24 |
|
|
721 error: evaluating assignment expression near line 1, column 22 |
|
|
722 error: called from `f' |
|
|
723 @end group |
|
|
724 @end example |
|
|
725 |
|
|
726 This error message has several parts, and gives you quite a bit of |
|
|
727 information to help you locate the source of the error. The messages |
|
|
728 are generated from the point of the innermost error, and provide a |
|
|
729 traceback of enclosing expressions and function calls. |
|
|
730 |
|
|
731 In the example above, the first line indicates that a variable named |
|
|
732 @samp{x} was found to be undefined near line 1 and column 24 of some |
|
|
733 function or expression. For errors occurring within functions, lines |
|
|
734 are counted from the beginning of the file containing the function |
|
|
735 definition. For errors occurring at the top level, the line number |
|
|
736 indicates the input line number, which is usually displayed in the |
|
|
737 prompt string. |
|
|
738 |
|
|
739 The second and third lines in the example indicate that the error |
|
|
740 occurred within an assignment expression, and the last line of the error |
|
|
741 message indicates that the error occurred within the function @code{f}. |
|
|
742 If the function @code{f} had been called from another function, for |
|
|
743 example, @code{g}, the list of errors would have ended with one more |
|
|
744 line: |
|
|
745 |
|
|
746 @example |
|
|
747 error: called from `g' |
|
|
748 @end example |
|
|
749 |
|
|
750 These lists of function calls usually make it fairly easy to trace the |
|
|
751 path your program took before the error occurred, and to correct the |
|
|
752 error before trying again. |
|
|
753 |
|
4167
|
754 @node Executable Octave Programs |
|
3294
|
755 @section Executable Octave Programs |
|
|
756 @cindex executable scripts |
|
|
757 @cindex scripts |
|
|
758 @cindex self contained programs |
|
|
759 @cindex program, self contained |
|
|
760 @cindex @samp{#!} |
|
|
761 |
|
|
762 Once you have learned Octave, you may want to write self-contained |
|
|
763 Octave scripts, using the @samp{#!} script mechanism. You can do this |
|
|
764 on GNU systems and on many Unix systems @footnote{The @samp{#!} |
|
|
765 mechanism works on Unix systems derived from Berkeley Unix, System V |
|
6481
|
766 Release 4, and some System V Release 3 systems.}. |
|
|
767 |
|
|
768 Self-contained Octave scripts are useful when you want to write a |
|
|
769 program which users can invoke without knowing that the program is |
|
|
770 written in the Octave language. |
|
3294
|
771 |
|
|
772 For example, you could create a text file named @file{hello}, containing |
|
|
773 the following lines: |
|
|
774 |
|
|
775 @example |
|
|
776 @group |
|
|
777 #! @var{octave-interpreter-name} -qf |
|
|
778 # a sample Octave program |
|
|
779 printf ("Hello, world!\n"); |
|
|
780 @end group |
|
|
781 @end example |
|
|
782 |
|
|
783 @noindent |
|
|
784 (where @var{octave-interpreter-name} should be replaced with the full |
|
6481
|
785 file name for your Octave binary). Note that this will only work if |
|
|
786 @samp{#!} appears at the very beginning of the file. After making this |
|
|
787 file executable |
|
3294
|
788 (with the @code{chmod} command), you can simply type: |
|
|
789 |
|
|
790 @example |
|
|
791 hello |
|
|
792 @end example |
|
|
793 |
|
|
794 @noindent |
|
|
795 at the shell, and the system will arrange to run Octave as if you had |
|
|
796 typed: |
|
|
797 |
|
|
798 @example |
|
|
799 octave hello |
|
|
800 @end example |
|
|
801 |
|
|
802 The line beginning with @samp{#!} lists the full file name of an |
|
|
803 interpreter to be run, and an optional initial command line argument to |
|
|
804 pass to that interpreter. The operating system then runs the |
|
|
805 interpreter with the given argument and the full argument list of the |
|
|
806 executed program. The first argument in the list is the full file name |
|
|
807 of the Octave program. The rest of the argument list will either be |
|
|
808 options to Octave, or data files, or both. The @samp{-qf} option is |
|
|
809 usually specified in stand-alone Octave programs to prevent them from |
|
|
810 printing the normal startup message, and to keep them from behaving |
|
|
811 differently depending on the contents of a particular user's |
|
6481
|
812 @file{~/.octaverc} file. @xref{Invoking Octave}. |
|
|
813 |
|
|
814 Note that some operating systems may place a limit on the number of |
|
|
815 characters that are recognized after @samp{#!}. Also, the various |
|
|
816 shells/systems parse differently the arguments appearing in a @samp{#!} |
|
|
817 line. The majority of them group together all the arguments in a string |
|
|
818 and pass it to the interepreter as a single argument. In this case, the |
|
|
819 following script: |
|
|
820 |
|
|
821 @example |
|
|
822 @group |
|
|
823 #! @var{octave-interpreter-name} -q -f # comment |
|
|
824 @end group |
|
|
825 @end example |
|
|
826 |
|
|
827 @noindent |
|
|
828 is equivalent to type at the command line: |
|
3294
|
829 |
|
6481
|
830 @example |
|
|
831 @group |
|
|
832 octave "-q -f # comment" |
|
|
833 @end group |
|
|
834 @end example |
|
3294
|
835 |
|
6481
|
836 @noindent |
|
|
837 which would obviously produce an error message. Unfortunately, it is |
|
|
838 impossible for Octave to know whether it has been called from the command |
|
|
839 line or from a @samp{#!} script, so some care is needed when using the |
|
|
840 @samp{#!} mechanism. |
|
|
841 |
|
|
842 Note that when Octave is started from an executable script, the built-in |
|
|
843 function @code{argv} returns a cell array containing the command line |
|
|
844 arguments passed to an executable Octave script, not the arguments |
|
|
845 passed to the Octave interpreter on the @samp{#!} line of the script. |
|
|
846 For example, the following program will reproduce the command line that |
|
|
847 is used to execute script, not @samp{-qf}. |
|
3294
|
848 |
|
|
849 @example |
|
|
850 @group |
|
|
851 #! /bin/octave -qf |
|
6479
|
852 printf ("%s", program_name ()); |
|
3294
|
853 for i = 1:nargin |
|
6479
|
854 arg_list = argv (); |
|
|
855 printf (" %s", arg_list@{i@}); |
|
3294
|
856 endfor |
|
|
857 printf ("\n"); |
|
|
858 @end group |
|
|
859 @end example |
|
|
860 |
|
4167
|
861 @node Comments |
|
3294
|
862 @section Comments in Octave Programs |
|
|
863 @cindex @samp{#} |
|
|
864 @cindex @samp{%} |
|
|
865 @cindex comments |
|
|
866 @cindex use of comments |
|
|
867 @cindex documenting Octave programs |
|
|
868 @cindex programs |
|
|
869 |
|
|
870 A @dfn{comment} is some text that is included in a program for the sake |
|
|
871 of human readers, and that is not really part of the program. Comments |
|
|
872 can explain what the program does, and how it works. Nearly all |
|
|
873 programming languages have provisions for comments, because programs are |
|
|
874 typically hard to understand without them. |
|
|
875 |
|
|
876 In the Octave language, a comment starts with either the sharp sign |
|
|
877 character, @samp{#}, or the percent symbol @samp{%} and continues to the |
|
|
878 end of the line. The Octave interpreter ignores the rest of a |
|
|
879 line following a sharp sign or percent symbol. For example, we could |
|
|
880 have put the following into the function @code{f}: |
|
|
881 |
|
|
882 @example |
|
|
883 @group |
|
|
884 function xdot = f (x, t) |
|
|
885 |
|
|
886 # usage: f (x, t) |
|
|
887 # |
|
|
888 # This function defines the right hand |
|
|
889 # side functions for a set of nonlinear |
|
|
890 # differential equations. |
|
|
891 |
|
|
892 r = 0.25; |
|
|
893 @dots{} |
|
|
894 endfunction |
|
|
895 @end group |
|
|
896 @end example |
|
|
897 |
|
|
898 The @code{help} command (@pxref{Getting Help}) is able to find the first |
|
|
899 block of comments in a function (even those that are composed directly |
|
|
900 on the command line). This means that users of Octave can use the same |
|
|
901 commands to get help for built-in functions, and for functions that you |
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902 have defined. For example, after defining the function @code{f} above, |
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903 the command @kbd{help f} produces the output |
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904 |
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905 @example |
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906 @group |
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907 usage: f (x, t) |
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908 |
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909 This function defines the right hand |
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910 side functions for a set of nonlinear |
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911 differential equations. |
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912 @end group |
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913 @end example |
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914 |
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915 Although it is possible to put comment lines into keyboard-composed |
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916 throw-away Octave programs, it usually isn't very useful, because the |
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917 purpose of a comment is to help you or another person understand the |
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918 program at a later time. |
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919 |
