D. Command Line Guidelines
Utilities have the following general usage:
utility [options] arguments
Typically, arguments is a set of filenames. If more than one file is specified, each filename is echoed to standard error as it is processed.
Options can either be:
- short style - these begin with a '-' character, or
- long-style - these begin with the character sequence '--'.
To obtain a concise summary of a utility's usage, execute it without any parameters. For example:
$ hoopy usage : hoopy [-h[help]] [-o[out_ext]] [-l[log_ext]] [-t thing,..] file ... purpose: do lots of hoopy things to files version: 1.000 $ _
The exit code returned to the operating system is dependent on the severity of any errors encountered during execution. The pre-defined exit codes are linked to message types as summarised below.
|8||warning||a possible problem was identified|
|16||error||an error was found|
|24||abort||processing could not continue on a file|
|32||fatal||the application terminated abnormally|
|64||failed||an internal error occurred|
The set of options is implicitly terminated by the first argument. i.e. the first symbol which does not begin with either '-' or '--'. To specify an argument which would otherwise be treated as an option, it is sometimes necessary to explicitly terminate the options using the '--' symbol.
Unless stated otherwise for a particular utility, '+' can be used to specify that standard input contains a list of arguments. This feature is particularly useful for passing complex arguments to scripts on systems with poor support for command line quoting.
If the arguments are files, '-' can be used to indicate standard input.
Default options for a utility can be specified in an environment variable of the form:
For example, if
HOOPYOPTS=-R/home/me/etc/reports export HOOPYOPTS
Several types of options are supported as outlined in the table below.
|Option type||Usage message format|
For parameter-optional options, the option parameter typically defaults to a particular value if the option is supplied without a parameter. For example, the extension of output files can be specified using the -o option. The default value of this parameter-optional option is 'out'. The series of examples below illustrates this.
- To send output to standard output:
- To send output to .out files:
hoopy -o *.dat
- To send output to .new files:
hoopy -onew *.dat
As for arguments, '-' can be specified to indicate standard input for options expecting a filename.
Some options have list parameters. These options can be specified several times and/or multiple list elements can be separated with commas. For example, the following are all equivalent:
hoopy -ta,b,c *.dat hoopy -ta -tb,c *.dat hoopy -ta,b -tc *.dat hoopy -ta -tb -tc *.dat
In addition to simple lists, lists of name-value pairs are also supported. In this case, the name and value are separated by a '=' or ':' character.
Note: on MS-DOS and OS/2, '=' causes problems so ':' must be used.
If only the name is given, the value is assumed to be 1. For example, the following are equivalent:
mycmd -ftbl_dir=../tables -fverbose=1 *.dat mycmd -ftbl_dir=../tables -fverbose *.dat mycmd -ftbl_dir:../tables -fverbose *.dat
Ordering is not important for name-value lists but may be important for normal lists. In either case, within a usage message, list options are indicated as follows:
There are two parameter styles: short and long. Short style is typically used on the command line. Long style is useful to improve readability in shell scripts.
In short style:
- options are specified by a single character
- a set of parameter-less options can be clustered
- between the option character and the parameter:
- whitespace is optional for a parameter-required option
- whitespace is not permitted for a parameter-optional option
In long style:
- the name can be abbreviated provided it is still unique
- a '=' or ':' is used to separate the option name from the parameter
hoopy --out *.dat
hoopy --out=new *.dat
Long option names should be selected for maximum readability. In general, the short name should be the first letter of the long name.
For list options which specify a set of directories to search in:
- the long name should end in '_path'
- the short name should be a capital letter
If applicable, the capital letter used should be taken from the related option. For example, if the -r option is used to specify a report file, the -R option should be the list of directories to search for the report in.
There are 3 options available for most utilities:
By default, generated output goes to standard output. To direct output to a file per input file, use the -o option to specify an extension for output files. If the -o option is specified without a parameter, an extension of out is assumed. Likewise, error messages go to standard error by default. Use the -l option to create a log file per input file. If the -l option is specified without a parameter, an extension of log is assumed.
For a small number of scripts, there is never a need for output or error files per argument. In this case, the -o and -l options are not available.
The -h option provides help and is always available. To obtain a concise description of each option, use the help option with no parameter. For example:
$ sdfget -h usage : sdfget [-h[help]] [-o[out_ext]] [-l[log_ext]] [-g get_rule] [-r[rpt_file]] [-i] file ... purpose: extract documentation embedded in source code version: 2.000 (SDF 2.000beta9) options: -h, --help display help on options -o, --out_ext output file extension -l, --log_ext log file extension -g, --get_rule rule to use to get documentation -r, --rpt_file report file -i, --inverse only output lines not extracted
Detailed help on a given option can be obtained by specifying the option code as a parameter to the -h option. For example:
$ sdfget -hg usage : sdfget [-h[help]] [-o[out_ext]] [-l[log_ext]] [-g get_rule] [-r[rpt_file]] [-i] file ... purpose: extract documentation embedded in source code version: 2.000 (SDF 2.000beta9) Detailed help on option: -g,--get_rule Attribute Value Help rule to use to get documentation Type STR Parameter yes Initial perl Legal table, perl, cpp, c, eiffel, fortran
The help option can also be used to obtain other useful information by specifying a special keyword as the parameter. The keywords supported are:
- .parts - display name & version of components (and exit)
- .time - display execution time (when exiting)
- .calltree - display the internal sequence of subroutines leading to utility exit
This type of information is useful when developing scripts but is rarely needed by end-users.