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1 @c Copyright (C) 1996, 1997, 1999, 2000, 2001, 2002, 2003, 2005, 2006, |
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2 @c 2007 John W. Eaton |
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3 @c |
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4 @c This file is part of Octave. |
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5 @c |
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6 @c Octave is free software; you can redistribute it and/or modify it |
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7 @c under the terms of the GNU General Public License as published by the |
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8 @c Free Software Foundation; either version 3 of the License, or (at |
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9 @c your option) any later version. |
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10 @c |
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11 @c Octave is distributed in the hope that it will be useful, but WITHOUT |
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12 @c ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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13 @c FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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14 @c for more details. |
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15 @c |
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16 @c You should have received a copy of the GNU General Public License |
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17 @c along with Octave; see the file COPYING. If not, see |
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18 @c <http://www.gnu.org/licenses/>. |
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19 |
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20 @node Getting Started |
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21 @chapter Getting Started |
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22 |
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23 This chapter explains some of Octave's basic features, including how to |
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24 start an Octave session, get help at the command prompt, edit the |
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25 command line, and write Octave programs that can be executed as commands |
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26 from your shell. |
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27 |
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28 @menu |
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29 * Invoking Octave from the Command Line:: |
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30 * Quitting Octave:: |
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31 * Getting Help:: |
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32 * Command Line Editing:: |
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33 * Errors:: |
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34 * Executable Octave Programs:: |
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35 * Comments:: |
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36 @end menu |
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37 |
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38 @node Invoking Octave from the Command Line |
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39 @section Invoking Octave from the Command Line |
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40 |
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41 Normally, Octave is used interactively by running the program |
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42 @samp{octave} without any arguments. Once started, Octave reads |
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43 commands from the terminal until you tell it to exit. |
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44 |
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45 You can also specify the name of a file on the command line, and Octave |
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46 will read and execute the commands from the named file and then exit |
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47 when it is finished. |
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48 |
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49 You can further control how Octave starts by using the command-line |
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50 options described in the next section, and Octave itself can remind you |
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51 of the options available. Type @samp{octave --help} to display all |
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52 available options and briefly describe their use (@samp{octave -h} is a |
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53 shorter equivalent). |
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54 |
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55 @menu |
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56 * Command Line Options:: |
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57 * Startup Files:: |
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58 @end menu |
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59 |
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60 @node Command Line Options |
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61 @subsection Command Line Options |
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62 @cindex Octave command options |
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63 @cindex command options |
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64 @cindex options, Octave command |
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65 |
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66 Here is a complete list of all the command line options that Octave |
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67 accepts. |
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68 |
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69 |
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70 @table @code |
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71 @item --debug |
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72 @itemx -d |
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73 @cindex @code{--debug} |
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74 @cindex @code{-d} |
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75 Enter parser debugging mode. Using this option will cause Octave's |
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76 parser to print a lot of information about the commands it reads, and is |
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77 probably only useful if you are actually trying to debug the parser. |
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78 |
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79 @item --echo-commands |
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80 @itemx -x |
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81 @cindex @code{--echo-commands} |
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82 @cindex @code{-x} |
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83 Echo commands as they are executed. |
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84 |
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85 @item --eval @var{code} |
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86 Evaluate @var{code} and exit when done unless @code{--persist} is also |
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87 specified. |
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88 |
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89 @item --exec-path @var{path} |
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90 @cindex @code{--exec-path @var{path}} |
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91 Specify the path to search for programs to run. The value of @var{path} |
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92 specified on the command line will override any value of |
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93 @code{OCTAVE_EXEC_PATH} found in the environment, but not any commands |
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94 in the system or user startup files that set the built-in variable |
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95 @code{EXEC_PATH}. |
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96 |
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97 @item --help |
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98 @itemx -h |
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99 @itemx -? |
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100 @cindex @code{--help} |
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101 @cindex @code{-h} |
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102 @cindex @code{-?} |
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103 Print short help message and exit. |
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104 |
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105 @item --image-path @var{path} |
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106 @cindex @code{--image-path @var{path}} |
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107 Specify the path to search for images. The value of @var{path} |
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108 specified on the command line will set the value of |
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109 @code{IMAGE_PATH} found in the environment. |
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110 |
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111 @item --info-file @var{filename} |
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112 @cindex @code{--info-file @var{filename}} |
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113 Specify the name of the info file to use. The value of @var{filename} |
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114 specified on the command line will override any value of |
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115 @code{OCTAVE_INFO_FILE} found in the environment, but not any commands |
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116 in the system or user startup files that use the @code{info_file} |
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117 function. |
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118 |
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119 @item --info-program @var{program} |
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120 @cindex @code{--info-program @var{program}} |
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121 Specify the name of the info program to use. The value of @var{program} |
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122 specified on the command line will override any value of |
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123 @code{OCTAVE_INFO_PROGRAM} found in the environment, but not any |
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124 commands in the system or user startup files that use the |
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125 @code{info_program} function. |
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126 |
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127 @item --interactive |
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128 @itemx -i |
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129 @cindex @code{--interactive} |
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130 @cindex @code{-i} |
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131 Force interactive behavior. This can be useful for running Octave via a |
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132 remote shell command or inside an Emacs shell buffer. For another way |
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133 to run Octave within Emacs, see @ref{Emacs}. |
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134 |
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135 @item --no-history |
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136 @itemx -H |
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137 Disable command-line history. |
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138 |
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139 @item --no-init-file |
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140 @cindex @code{--no-init-file} |
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141 Don't read the @file{~/.octaverc} or @file{.octaverc} files. |
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142 |
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143 @item --no-line-editing |
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144 @cindex @code{--no-line-editing} |
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145 Disable command-line editing. |
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146 |
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147 @item --no-site-file |
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148 @cindex @code{--no-site-file} |
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149 Don't read the site-wide @file{octaverc} file. |
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150 |
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151 @item --norc |
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152 @itemx -f |
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153 @cindex @code{--norc} |
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154 @cindex @code{-f} |
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155 Don't read any of the system or user initialization files at startup. |
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156 This is equivalent to using both of the options @code{--no-init-file} |
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157 and @code{--no-site-file}. |
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158 |
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159 @item --path @var{path} |
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160 @itemx -p @var{path} |
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161 @cindex @code{--path @var{path}} |
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162 @cindex @code{-p @var{path}} |
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163 Specify the path to search for function files. The value of @var{path} |
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164 specified on the command line will override any value of |
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165 @code{OCTAVE_PATH} found in the environment, but not any commands in the |
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166 system or user startup files that set the internal load path through one |
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167 of the path functions. |
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168 |
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169 @item --persist |
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170 Go to interactive mode after @code{--eval} or reading from a file |
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171 named on the command line. |
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172 |
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173 @item --silent |
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174 @itemx --quiet |
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175 @itemx -q |
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176 @cindex @code{--silent} |
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177 @cindex @code{--quiet} |
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178 @cindex @code{-q} |
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179 Don't print the usual greeting and version message at startup. |
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180 |
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181 @item --traditional |
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182 @itemx --braindead |
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183 @cindex @code{--traditional} |
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184 @cindex @code{--braindead} |
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185 For compatibility with @sc{Matlab}, set initial values for |
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186 user-preferences to the following values |
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187 |
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188 @example |
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189 @group |
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190 PS1 = ">> " |
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191 PS2 = "" |
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192 beep_on_error = true |
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193 crash_dumps_octave_core = false |
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194 default_save_options = "-mat-binary" |
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195 fixed_point_format = true |
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196 history_timestamp_format_string |
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197 = "%%-- %D %I:%M %p --%%" |
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198 page_screen_output = false |
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199 print_empty_dimensions = false |
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200 @end group |
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201 @end example |
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202 |
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203 @noindent |
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204 and disable the following warnings |
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205 @example |
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206 @group |
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207 Octave:fopen-file-in-path |
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208 Octave:function-name-clash |
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209 Octave:load-file-in-path |
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210 @end group |
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211 @end example |
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212 |
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213 @item --verbose |
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214 @itemx -V |
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215 @cindex @code{--verbose} |
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216 @cindex @code{-V} |
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217 Turn on verbose output. |
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218 |
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219 @item --version |
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220 @itemx -v |
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221 @cindex @code{--version} |
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222 @cindex @code{-v} |
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223 Print the program version number and exit. |
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224 |
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225 @item @var{file} |
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226 Execute commands from @var{file}. Exit when done unless |
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227 @code{--persist} is also specified. |
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228 @end table |
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229 |
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230 Octave also includes several built-in variables that contain information |
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231 about the command line, including the number of arguments and all of the |
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232 options. |
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233 |
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234 @DOCSTRING(argv) |
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235 |
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236 @DOCSTRING(program_name) |
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237 |
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238 @DOCSTRING(program_invocation_name) |
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239 |
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240 Here is an example of using these functions to reproduce Octave's |
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241 command line. |
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242 |
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243 @example |
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244 printf ("%s", program_name ()); |
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245 arg_list = argv (); |
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246 for i = 1:nargin |
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247 printf (" %s", arg_list@{i@}); |
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248 endfor |
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249 printf ("\n"); |
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250 @end example |
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251 |
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252 @noindent |
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253 @xref{Index Expressions}, for an explanation of how to properly index |
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254 arrays of strings and substrings in Octave, and @xref{Defining Functions}, |
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255 for information about the variable @code{nargin}. |
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256 |
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257 @node Startup Files |
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258 @subsection Startup Files |
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259 @cindex initialization |
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260 @cindex startup |
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261 |
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262 When Octave starts, it looks for commands to execute from the files in |
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263 the following list. These files may contain any valid Octave commands, |
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264 including function definitions. |
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265 |
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266 @cindex startup files |
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267 |
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268 @table @code |
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269 @item @var{octave-home}/share/octave/site/m/startup/octaverc |
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270 Where @var{octave-home} is the directory in which all of Octave is |
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271 installed (the default is @file{@value{OCTAVEHOME}}). This file is |
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272 provided so that changes to the default Octave environment can be made |
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273 globally for all users at your site for all versions of Octave you have |
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274 installed. Some care should be taken when making changes to this file, |
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275 since all users of Octave at your site will be affected. |
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276 |
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277 @item @var{octave-home}/share/octave/@var{version}/m/startup/octaverc |
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278 Where @var{octave-home} is the directory in which all of Octave is |
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279 installed (the default is @file{@value{OCTAVEHOME}}), and @var{version} |
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280 is the version number of Octave. This file is provided so that changes |
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281 to the default Octave environment can be made globally for all users for |
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282 a particular version of Octave. Some care should be taken when making |
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283 changes to this file, since all users of Octave at your site will be |
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284 affected. |
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285 |
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286 @item ~/.octaverc |
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287 @cindex @code{~/.octaverc} |
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288 This file is normally used to make personal changes to the default |
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289 Octave environment. |
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290 |
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291 @item .octaverc |
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292 @cindex @code{.octaverc} |
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293 This file can be used to make changes to the default Octave environment |
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294 for a particular project. Octave searches for this file in the current |
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295 directory after it reads @file{~/.octaverc}. Any use of the @code{cd} |
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296 command in the @file{~/.octaverc} file will affect the directory that |
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297 Octave searches for the file @file{.octaverc}. |
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298 |
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299 If you start Octave in your home directory, commands from from the file |
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300 @file{~/.octaverc} will only be executed once. |
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301 @end table |
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302 |
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303 A message will be displayed as each of the startup files is read if you |
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304 invoke Octave with the @code{--verbose} option but without the |
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305 @code{--silent} option. |
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306 |
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307 @node Quitting Octave |
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308 @section Quitting Octave |
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309 @cindex exiting octave |
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310 @cindex quitting octave |
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311 |
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312 @DOCSTRING(quit) |
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313 |
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314 @DOCSTRING(atexit) |
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315 |
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316 @node Getting Help |
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317 @section Commands for Getting Help |
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318 @cindex on-line help |
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319 @cindex help, on-line |
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320 |
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321 The entire text of this manual is available from the Octave prompt |
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322 via the command @kbd{doc}. In addition, the documentation for |
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323 individual user-written functions and variables is also available via |
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324 the @kbd{help} command. This section describes the commands used for |
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325 reading the manual and the documentation strings for user-supplied |
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326 functions and variables. @xref{Function Files}, for more information |
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327 about how to document the functions you write. |
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328 |
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329 @DOCSTRING(help) |
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330 |
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331 @DOCSTRING(doc) |
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332 |
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333 @DOCSTRING(lookfor) |
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334 |
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335 The following function can be used to change which programs are used |
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336 for displaying the documentation, and where the documentation can be |
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337 found. |
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338 |
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339 @DOCSTRING(info_file) |
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340 |
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341 @DOCSTRING(info_program) |
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342 |
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343 @DOCSTRING(makeinfo_program) |
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344 |
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345 @DOCSTRING(suppress_verbose_help_message) |
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346 |
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347 @node Command Line Editing |
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348 @section Command Line Editing |
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349 @cindex command-line editing |
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350 @cindex editing the command line |
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351 |
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352 Octave uses the GNU readline library to provide an extensive set of |
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353 command-line editing and history features. Only the most common |
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354 features are described in this manual. Please see The GNU Readline |
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355 Library manual for more information. |
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356 |
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357 To insert printing characters (letters, digits, symbols, etc.), simply |
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358 type the character. Octave will insert the character at the cursor and |
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359 advance the cursor forward. |
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360 |
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361 Many of the command-line editing functions operate using control |
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362 characters. For example, the character @kbd{Control-a} moves the cursor |
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363 to the beginning of the line. To type @kbd{C-a}, hold down @key{CTRL} |
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364 and then press @key{a}. In the following sections, control characters |
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365 such as @kbd{Control-a} are written as @kbd{C-a}. |
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366 |
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367 Another set of command-line editing functions use Meta characters. On |
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368 some terminals, you type @kbd{M-u} by holding down @key{META} and |
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369 pressing @key{u}. If your terminal does not have a @key{META} key, you |
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370 can still type Meta characters using two-character sequences starting |
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371 with @kbd{ESC}. Thus, to enter @kbd{M-u}, you could type |
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372 @key{ESC}@key{u}. The @kbd{ESC} character sequences are also allowed on |
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373 terminals with real Meta keys. In the following sections, Meta |
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374 characters such as @kbd{Meta-u} are written as @kbd{M-u}. |
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375 |
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376 |
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377 @menu |
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378 * Cursor Motion:: |
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379 * Killing and Yanking:: |
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380 * Commands For Text:: |
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381 * Commands For Completion:: |
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382 * Commands For History:: |
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383 * Customizing readline:: |
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384 * Customizing the Prompt:: |
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385 * Diary and Echo Commands:: |
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386 @end menu |
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387 |
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388 @node Cursor Motion |
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389 @subsection Cursor Motion |
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390 |
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391 The following commands allow you to position the cursor. |
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392 |
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393 @table @kbd |
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394 @item C-b |
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395 Move back one character. |
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396 |
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397 @item C-f |
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398 Move forward one character. |
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399 |
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400 @item @key{DEL} |
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401 Delete the character to the left of the cursor. |
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402 |
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403 @item C-d |
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404 Delete the character underneath the cursor. |
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405 |
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406 @item M-f |
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407 Move forward a word. |
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408 |
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409 @item M-b |
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410 Move backward a word. |
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411 |
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412 @item C-a |
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413 Move to the start of the line. |
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414 |
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415 @item C-e |
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416 Move to the end of the line. |
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417 |
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418 @item C-l |
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419 Clear the screen, reprinting the current line at the top. |
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420 |
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421 @item C-_ |
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422 @itemx C-/ |
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423 Undo the last thing that you did. You can undo all the way back to an |
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424 empty line. |
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425 |
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426 @item M-r |
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427 Undo all changes made to this line. This is like typing the `undo' |
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428 command enough times to get back to the beginning. |
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429 @end table |
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430 |
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431 The above table describes the most basic possible keystrokes that you need |
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432 in order to do editing of the input line. On most terminals, you can |
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433 also use the arrow keys in place of @kbd{C-f} and @kbd{C-b} to move |
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434 forward and backward. |
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435 |
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436 Notice how @kbd{C-f} moves forward a character, while @kbd{M-f} moves |
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437 forward a word. It is a loose convention that control keystrokes |
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438 operate on characters while meta keystrokes operate on words. |
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439 |
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440 @cindex clearing the screen |
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441 |
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442 The function @code{clc} will allow you to clear the screen from within |
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443 Octave programs. |
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444 |
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445 @ifinfo |
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446 @DOCSTRING(clc) |
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447 @end ifinfo |
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448 |
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449 @node Killing and Yanking |
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450 @subsection Killing and Yanking |
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451 |
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452 @dfn{Killing} text means to delete the text from the line, but to save |
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453 it away for later use, usually by @dfn{yanking} it back into the line. |
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454 If the description for a command says that it `kills' text, then you can |
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455 be sure that you can get the text back in a different (or the same) |
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456 place later. |
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457 |
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458 Here is the list of commands for killing text. |
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459 |
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460 @table @kbd |
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461 @item C-k |
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462 Kill the text from the current cursor position to the end of the line. |
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463 |
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464 @item M-d |
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465 Kill from the cursor to the end of the current word, or if between |
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466 words, to the end of the next word. |
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467 |
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468 @item M-@key{DEL} |
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469 Kill from the cursor to the start of the previous word, or if between |
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470 words, to the start of the previous word. |
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471 |
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472 @item C-w |
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473 Kill from the cursor to the previous whitespace. This is different than |
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474 @kbd{M-@key{DEL}} because the word boundaries differ. |
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475 @end table |
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476 |
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477 And, here is how to @dfn{yank} the text back into the line. Yanking |
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478 means to copy the most-recently-killed text from the kill buffer. |
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479 |
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480 @table @kbd |
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481 @item C-y |
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482 Yank the most recently killed text back into the buffer at the cursor. |
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483 |
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484 @item M-y |
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485 Rotate the kill-ring, and yank the new top. You can only do this if |
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486 the prior command is @kbd{C-y} or @kbd{M-y}. |
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487 @end table |
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488 |
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489 When you use a kill command, the text is saved in a @dfn{kill-ring}. |
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490 Any number of consecutive kills save all of the killed text together, so |
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491 that when you yank it back, you get it in one clean sweep. The kill |
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492 ring is not line specific; the text that you killed on a previously |
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493 typed line is available to be yanked back later, when you are typing |
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494 another line. |
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495 |
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496 @node Commands For Text |
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497 @subsection Commands For Changing Text |
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498 |
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499 The following commands can be used for entering characters that would |
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500 otherwise have a special meaning (e.g., @kbd{TAB}, @kbd{C-q}, etc.), or |
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501 for quickly correcting typing mistakes. |
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502 |
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503 @table @kbd |
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504 @item C-q |
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505 @itemx C-v |
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506 Add the next character that you type to the line verbatim. This is |
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507 how to insert things like @kbd{C-q} for example. |
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508 |
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509 @item M-@key{TAB} |
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510 Insert a tab character. |
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511 |
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512 @item C-t |
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513 Drag the character before the cursor forward over the character at the |
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514 cursor, also moving the cursor forward. If the cursor is at the end of |
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515 the line, then transpose the two characters before it. |
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516 |
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517 @item M-t |
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518 Drag the word behind the cursor past the word in front of the cursor |
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519 moving the cursor over that word as well. |
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520 |
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521 @item M-u |
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522 Uppercase the characters following the cursor to the end of the current |
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523 (or following) word, moving the cursor to the end of the word. |
|
524 |
|
525 @item M-l |
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|
526 Lowercase the characters following the cursor to the end of the current |
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|
527 (or following) word, moving the cursor to the end of the word. |
|
528 |
|
529 @item M-c |
|
530 Uppercase the character following the cursor (or the beginning of the |
|
531 next word if the cursor is between words), moving the cursor to the end |
|
532 of the word. |
|
533 @end table |
|
534 |
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|
535 @node Commands For Completion |
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|
536 @subsection Letting Readline Type For You |
|
537 @cindex command completion |
|
538 |
|
539 The following commands allow Octave to complete command and variable |
|
540 names for you. |
|
541 |
|
542 @table @kbd |
|
543 @item @key{TAB} |
|
544 Attempt to do completion on the text before the cursor. Octave can |
|
545 complete the names of commands and variables. |
|
546 |
|
547 @item M-? |
|
548 List the possible completions of the text before the cursor. |
|
549 @end table |
|
550 |
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|
551 @DOCSTRING(completion_append_char) |
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|
552 |
3332
|
553 @DOCSTRING(completion_matches) |
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|
554 |
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|
555 @node Commands For History |
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|
556 @subsection Commands For Manipulating The History |
|
557 @cindex command history |
|
558 @cindex input history |
|
559 @cindex history of commands |
|
560 |
|
561 Octave normally keeps track of the commands you type so that you can |
|
562 recall previous commands to edit or execute them again. When you exit |
|
563 Octave, the most recent commands you have typed, up to the number |
|
564 specified by the variable @code{history_size}, are saved in a file. |
|
565 When Octave starts, it loads an initial list of commands from the file |
|
566 named by the variable @code{history_file}. |
|
567 |
|
568 Here are the commands for simple browsing and searching the history |
|
569 list. |
|
570 |
|
571 @table @kbd |
|
572 @item @key{LFD} |
|
573 @itemx @key{RET} |
|
574 Accept the line regardless of where the cursor is. If this line is |
|
575 non-empty, add it to the history list. If this line was a history |
|
576 line, then restore the history line to its original state. |
|
577 |
|
578 @item C-p |
|
579 Move `up' through the history list. |
|
580 |
|
581 @item C-n |
|
582 Move `down' through the history list. |
|
583 |
|
584 @item M-< |
|
585 Move to the first line in the history. |
|
586 |
|
587 @item M-> |
|
588 Move to the end of the input history, i.e., the line you are entering! |
|
589 |
|
590 @item C-r |
|
591 Search backward starting at the current line and moving `up' through |
|
592 the history as necessary. This is an incremental search. |
|
593 |
|
594 @item C-s |
|
595 Search forward starting at the current line and moving `down' through |
|
596 the history as necessary. |
|
597 @end table |
|
598 |
|
599 On most terminals, you can also use the arrow keys in place of @kbd{C-p} |
|
600 and @kbd{C-n} to move through the history list. |
|
601 |
|
602 In addition to the keyboard commands for moving through the history |
|
603 list, Octave provides three functions for viewing, editing, and |
|
604 re-running chunks of commands from the history list. |
|
605 |
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|
606 @DOCSTRING(history) |
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|
607 |
3332
|
608 @DOCSTRING(edit_history) |
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|
609 |
3332
|
610 @DOCSTRING(run_history) |
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|
611 |
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|
612 Octave also allows you customize the details of how and where the history |
|
613 is saved. |
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|
614 |
3332
|
615 @DOCSTRING(history_file) |
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|
616 |
3332
|
617 @DOCSTRING(history_size) |
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|
618 |
3332
|
619 @DOCSTRING(saving_history) |
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|
620 |
6550
|
621 @DOCSTRING(history_timestamp_format_string) |
|
622 |
6620
|
623 @DOCSTRING(EDITOR) |
|
624 |
4167
|
625 @node Customizing readline |
3428
|
626 @subsection Customizing @code{readline} |
|
627 |
6620
|
628 As mentioned earlier Octave uses the GNU readline library for |
|
629 command-line editing and history features. It is possible to |
|
630 customize how readline works through a configuration file. |
|
631 |
5775
|
632 @c FIXME -- need a brief description of the ~/.inputrc file here. |
3428
|
633 |
3439
|
634 @DOCSTRING(read_readline_init_file) |
3428
|
635 |
4167
|
636 @node Customizing the Prompt |
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|
637 @subsection Customizing the Prompt |
|
638 @cindex prompt customization |
|
639 @cindex customizing the prompt |
|
640 |
|
641 The following variables are available for customizing the appearance of |
|
642 the command-line prompts. Octave allows the prompt to be customized by |
|
643 inserting a number of backslash-escaped special characters that are |
|
644 decoded as follows: |
|
645 |
|
646 @table @samp |
|
647 @item \t |
|
648 The time. |
|
649 |
|
650 @item \d |
|
651 The date. |
|
652 |
|
653 @item \n |
|
654 Begins a new line by printing the equivalent of a carriage return |
|
655 followed by a line feed. |
|
656 |
|
657 @item \s |
|
658 The name of the program (usually just @samp{octave}). |
|
659 |
|
660 @item \w |
|
661 The current working directory. |
|
662 |
|
663 @item \W |
|
664 The basename of the current working directory. |
|
665 |
|
666 @item \u |
|
667 The username of the current user. |
|
668 |
|
669 @item \h |
|
670 The hostname, up to the first `.'. |
|
671 |
|
672 @item \H |
|
673 The hostname. |
|
674 |
|
675 @item \# |
|
676 The command number of this command, counting from when Octave starts. |
|
677 |
|
678 @item \! |
|
679 The history number of this command. This differs from @samp{\#} by the |
|
680 number of commands in the history list when Octave starts. |
|
681 |
|
682 @item \$ |
|
683 If the effective UID is 0, a @samp{#}, otherwise a @samp{$}. |
|
684 |
|
685 @item \nnn |
|
686 The character whose character code in octal is @var{nnn}. |
|
687 |
|
688 @item \\ |
|
689 A backslash. |
|
690 @end table |
|
691 |
3332
|
692 @DOCSTRING(PS1) |
3294
|
693 |
3332
|
694 @DOCSTRING(PS2) |
3294
|
695 |
3332
|
696 @DOCSTRING(PS4) |
3294
|
697 |
4167
|
698 @node Diary and Echo Commands |
3294
|
699 @subsection Diary and Echo Commands |
|
700 @cindex diary of commands and output |
6939
|
701 @cindex command and output logs |
3294
|
702 @cindex logging commands and output |
|
703 @cindex echoing executing commands |
|
704 @cindex command echoing |
|
705 |
|
706 Octave's diary feature allows you to keep a log of all or part of an |
|
707 interactive session by recording the input you type and the output that |
|
708 Octave produces in a separate file. |
|
709 |
3332
|
710 @DOCSTRING(diary) |
3294
|
711 |
|
712 Sometimes it is useful to see the commands in a function or script as |
|
713 they are being evaluated. This can be especially helpful for debugging |
|
714 some kinds of problems. |
|
715 |
3332
|
716 @DOCSTRING(echo) |
3294
|
717 |
3332
|
718 @DOCSTRING(echo_executing_commands) |
3294
|
719 |
4167
|
720 @node Errors |
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|
721 @section How Octave Reports Errors |
|
722 @cindex error messages |
|
723 @cindex messages, error |
|
724 |
|
725 Octave reports two kinds of errors for invalid programs. |
|
726 |
|
727 A @dfn{parse error} occurs if Octave cannot understand something you |
|
728 have typed. For example, if you misspell a keyword, |
|
729 |
|
730 @example |
|
731 octave:13> functon y = f (x) y = x^2; endfunction |
|
732 @end example |
|
733 |
|
734 @noindent |
|
735 Octave will respond immediately with a message like this: |
|
736 |
|
737 @example |
|
738 parse error: |
|
739 |
|
740 functon y = f (x) y = x^2; endfunction |
|
741 ^ |
|
742 @end example |
|
743 |
|
744 @noindent |
|
745 For most parse errors, Octave uses a caret (@samp{^}) to mark the point |
|
746 on the line where it was unable to make sense of your input. In this |
|
747 case, Octave generated an error message because the keyword |
|
748 @code{function} was misspelled. Instead of seeing @samp{function f}, |
|
749 Octave saw two consecutive variable names, which is invalid in this |
|
750 context. It marked the error at @code{y} because the first name by |
|
751 itself was accepted as valid input. |
|
752 |
|
753 Another class of error message occurs at evaluation time. These |
|
754 errors are called @dfn{run-time errors}, or sometimes |
|
755 @dfn{evaluation errors} because they occur when your program is being |
|
756 @dfn{run}, or @dfn{evaluated}. For example, if after correcting the |
|
757 mistake in the previous function definition, you type |
|
758 |
|
759 @example |
|
760 octave:13> f () |
|
761 @end example |
|
762 |
|
763 @noindent |
|
764 Octave will respond with |
|
765 |
7031
|
766 @c Using 'smallexample' to make text fit on page when creating smallbook. |
|
767 @smallexample |
3294
|
768 @group |
|
769 error: `x' undefined near line 1 column 24 |
|
770 error: evaluating expression near line 1, column 24 |
|
771 error: evaluating assignment expression near line 1, column 22 |
|
772 error: called from `f' |
|
773 @end group |
7031
|
774 @end smallexample |
3294
|
775 |
6620
|
776 @noindent |
3294
|
777 This error message has several parts, and gives you quite a bit of |
|
778 information to help you locate the source of the error. The messages |
|
779 are generated from the point of the innermost error, and provide a |
|
780 traceback of enclosing expressions and function calls. |
|
781 |
|
782 In the example above, the first line indicates that a variable named |
|
783 @samp{x} was found to be undefined near line 1 and column 24 of some |
|
784 function or expression. For errors occurring within functions, lines |
|
785 are counted from the beginning of the file containing the function |
|
786 definition. For errors occurring at the top level, the line number |
|
787 indicates the input line number, which is usually displayed in the |
|
788 prompt string. |
|
789 |
|
790 The second and third lines in the example indicate that the error |
|
791 occurred within an assignment expression, and the last line of the error |
|
792 message indicates that the error occurred within the function @code{f}. |
|
793 If the function @code{f} had been called from another function, for |
|
794 example, @code{g}, the list of errors would have ended with one more |
|
795 line: |
|
796 |
|
797 @example |
|
798 error: called from `g' |
|
799 @end example |
|
800 |
|
801 These lists of function calls usually make it fairly easy to trace the |
|
802 path your program took before the error occurred, and to correct the |
|
803 error before trying again. |
|
804 |
4167
|
805 @node Executable Octave Programs |
3294
|
806 @section Executable Octave Programs |
|
807 @cindex executable scripts |
|
808 @cindex scripts |
|
809 @cindex self contained programs |
|
810 @cindex program, self contained |
|
811 @cindex @samp{#!} |
|
812 |
|
813 Once you have learned Octave, you may want to write self-contained |
|
814 Octave scripts, using the @samp{#!} script mechanism. You can do this |
|
815 on GNU systems and on many Unix systems @footnote{The @samp{#!} |
|
816 mechanism works on Unix systems derived from Berkeley Unix, System V |
6481
|
817 Release 4, and some System V Release 3 systems.}. |
|
818 |
|
819 Self-contained Octave scripts are useful when you want to write a |
|
820 program which users can invoke without knowing that the program is |
|
821 written in the Octave language. |
3294
|
822 |
|
823 For example, you could create a text file named @file{hello}, containing |
|
824 the following lines: |
|
825 |
|
826 @example |
|
827 @group |
|
828 #! @var{octave-interpreter-name} -qf |
|
829 # a sample Octave program |
|
830 printf ("Hello, world!\n"); |
|
831 @end group |
|
832 @end example |
|
833 |
|
834 @noindent |
|
835 (where @var{octave-interpreter-name} should be replaced with the full |
6481
|
836 file name for your Octave binary). Note that this will only work if |
|
837 @samp{#!} appears at the very beginning of the file. After making this |
|
838 file executable |
3294
|
839 (with the @code{chmod} command), you can simply type: |
|
840 |
|
841 @example |
|
842 hello |
|
843 @end example |
|
844 |
|
845 @noindent |
|
846 at the shell, and the system will arrange to run Octave as if you had |
|
847 typed: |
|
848 |
|
849 @example |
|
850 octave hello |
|
851 @end example |
|
852 |
|
853 The line beginning with @samp{#!} lists the full file name of an |
|
854 interpreter to be run, and an optional initial command line argument to |
|
855 pass to that interpreter. The operating system then runs the |
|
856 interpreter with the given argument and the full argument list of the |
|
857 executed program. The first argument in the list is the full file name |
|
858 of the Octave program. The rest of the argument list will either be |
|
859 options to Octave, or data files, or both. The @samp{-qf} option is |
|
860 usually specified in stand-alone Octave programs to prevent them from |
|
861 printing the normal startup message, and to keep them from behaving |
|
862 differently depending on the contents of a particular user's |
6620
|
863 @file{~/.octaverc} file. @xref{Invoking Octave from the Command Line}. |
6481
|
864 |
|
865 Note that some operating systems may place a limit on the number of |
|
866 characters that are recognized after @samp{#!}. Also, the various |
|
867 shells/systems parse differently the arguments appearing in a @samp{#!} |
|
868 line. The majority of them group together all the arguments in a string |
6939
|
869 and pass it to the interpreter as a single argument. In this case, the |
6481
|
870 following script: |
|
871 |
|
872 @example |
|
873 @group |
|
874 #! @var{octave-interpreter-name} -q -f # comment |
|
875 @end group |
|
876 @end example |
|
877 |
|
878 @noindent |
|
879 is equivalent to type at the command line: |
3294
|
880 |
6481
|
881 @example |
|
882 @group |
|
883 octave "-q -f # comment" |
|
884 @end group |
|
885 @end example |
3294
|
886 |
6481
|
887 @noindent |
|
888 which would obviously produce an error message. Unfortunately, it is |
|
889 impossible for Octave to know whether it has been called from the command |
|
890 line or from a @samp{#!} script, so some care is needed when using the |
|
891 @samp{#!} mechanism. |
|
892 |
|
893 Note that when Octave is started from an executable script, the built-in |
|
894 function @code{argv} returns a cell array containing the command line |
|
895 arguments passed to an executable Octave script, not the arguments |
|
896 passed to the Octave interpreter on the @samp{#!} line of the script. |
|
897 For example, the following program will reproduce the command line that |
|
898 is used to execute script, not @samp{-qf}. |
3294
|
899 |
|
900 @example |
|
901 @group |
|
902 #! /bin/octave -qf |
6479
|
903 printf ("%s", program_name ()); |
6620
|
904 arg_list = argv (); |
3294
|
905 for i = 1:nargin |
6479
|
906 printf (" %s", arg_list@{i@}); |
3294
|
907 endfor |
|
908 printf ("\n"); |
|
909 @end group |
|
910 @end example |
|
911 |
4167
|
912 @node Comments |
3294
|
913 @section Comments in Octave Programs |
|
914 @cindex @samp{#} |
|
915 @cindex @samp{%} |
|
916 @cindex comments |
|
917 @cindex use of comments |
|
918 @cindex documenting Octave programs |
|
919 @cindex programs |
|
920 |
|
921 A @dfn{comment} is some text that is included in a program for the sake |
|
922 of human readers, and that is not really part of the program. Comments |
|
923 can explain what the program does, and how it works. Nearly all |
|
924 programming languages have provisions for comments, because programs are |
|
925 typically hard to understand without them. |
|
926 |
|
927 In the Octave language, a comment starts with either the sharp sign |
|
928 character, @samp{#}, or the percent symbol @samp{%} and continues to the |
|
929 end of the line. The Octave interpreter ignores the rest of a |
|
930 line following a sharp sign or percent symbol. For example, we could |
|
931 have put the following into the function @code{f}: |
|
932 |
|
933 @example |
|
934 @group |
|
935 function xdot = f (x, t) |
|
936 |
|
937 # usage: f (x, t) |
|
938 # |
|
939 # This function defines the right hand |
|
940 # side functions for a set of nonlinear |
|
941 # differential equations. |
|
942 |
|
943 r = 0.25; |
|
944 @dots{} |
|
945 endfunction |
|
946 @end group |
|
947 @end example |
|
948 |
|
949 The @code{help} command (@pxref{Getting Help}) is able to find the first |
|
950 block of comments in a function (even those that are composed directly |
|
951 on the command line). This means that users of Octave can use the same |
|
952 commands to get help for built-in functions, and for functions that you |
|
953 have defined. For example, after defining the function @code{f} above, |
|
954 the command @kbd{help f} produces the output |
|
955 |
|
956 @example |
|
957 @group |
|
958 usage: f (x, t) |
|
959 |
|
960 This function defines the right hand |
|
961 side functions for a set of nonlinear |
|
962 differential equations. |
|
963 @end group |
|
964 @end example |
|
965 |
|
966 Although it is possible to put comment lines into keyboard-composed |
|
967 throw-away Octave programs, it usually isn't very useful, because the |
|
968 purpose of a comment is to help you or another person understand the |
|
969 program at a later time. |
|
970 |