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Invocation

Ae recognises the following flags on invocation:

`-i'

Ensures that the shell runs in interactive mode. The primary effects of this mode are to activate the user interface for entering commands, and to respond to syntax errors by asking for a new command rather than exitting. Other effects are discussed below in more relevant context. Interactive mode is the default if input is being read from a terminal.

`-s'

The shell reads commands from standard input rather than from a shell script. This is needed if arguments are given on the command line. Without the `-s' flag the first argument after the flags is taken to be a file from which to read commands.

`-e'

Shell will exit immediately if any command returns a non-zero (erroneous) status (This probably isn't the case at the moment).

`-k'

Assignment words (see section Parsing) are recognised anywhere in a command line rather than only at the beginning. (NOT IMPLEMENTED)

`-n'

Read and parse commands but do not execute them. This allows for syntactic checking of shell scripts.

`-t'

Only the first command read is executed and it is performed by an exec, if possible, to save one process.

`-u'

Unset variables are regarded as errors when substituting.

`-v'

Verbose mode. Every line of input is printed after it is read. To aid with syntax checking, each line is preceded by one or two numbers. The first number indicates the level of nesting of complex commands before that line was parsed, and the second, if present, indicates the depth of quoting before the line is parsed.

`-x'

Trace mode. Each command and its arguments is printed before being executed. Should say more here.

`-c'

Input is taken from the text of the next argument rather than from a file.

If there are further arguments, the first is used as the name of a file to take input from unless the `c' or `s' flags are given. Any remaining arguments are assigned to the variable ARGV (see section Reserved Variable Names).

The value of the zeroth argument (the name the program was called under) can also affect the execution of ae. If this argument starts with a hyphen (as is the case for any login shell) then ae reads commands from the files `/etc/profile' and `.profile' in the users home directory, if these files exist.

Initialisation commands are also read from the environment variable SHELLRC if the shell is interactive.

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