`uesh`

Micro-embedded shell (QNX)

Syntax:

uesh [script_file]

Options:

script_file: A file containing shell commands to execute.

The uesh utility provides a subset of the functionality found in the standard QNX embedded shell, /bin/esh. You should find uesh useful for situations where memory requirements are limited. For example, you could use it to run a simple system initialization file for an embedded system.

The micro-embedded shell has some very significant limitations. These include:

No interactive mode.
No pipes.
No aliases.
No filename or command completion.
No set command.

For applications that require greater functionality, use esh or the full shell, sh.

Command-line format

In uesh, command lines take this form:

[//node] command arg1 arg2 ... [redir-op file] [&]

Where:

//node

The node the command is to be executed on. Remote execution isn't allowed in restricted mode.

command

The command to be executed. If it doesn't start with a slash, the command will follow the path set by the PATH environment variable. In restricted mode, a command can't start with a slash.

redir-op file

A redirection operator. When a command is invoked, three standard files are set up in its environment. These files, standard input, standard output, and standard error output (stdin, stdout, stderr), are usually attached to the active terminal. You can redirect a command's standard input, standard output, and standard error as follows:

Specifying:	Will:
`<`file	redirect standard input from this file.
`>`file	redirect standard output to this file. If the file exists, it's overwritten; if the file doesn't exist, it's created.
`>>`file	redirect standard output to this file. If the file exists, the information is appended to the end of the file; if the file doesn't exist, it's created.
`2>`file	do the same as `>`file, but for standard error.
`2>>`file	do the same as `>>`file, but for standard error.
`&`	If a command contains an unquoted &, then `uesh` doesn't wait for the command to complete execution but immediately moves on to process the next command. The standard input of the command is redirected from `/dev/null`, and SIGINT and SIGQUIT are ignored.

Filename expansion

The uesh shell does not support filename expansion. Such shorthands as *.c for all files ended in .c will not work.

Quoting

The following characters have a special meaning in uesh:

    &  \  "  *  ?  [  space

To suppress the special meaning of these characters and keep their literal meaning, you use quoting.

To quote a sequence of characters or sequence of words, enclose the sequence in double quotes. To quote a single character, use double quotes or precede it with the escape character (\).

Escape character (backslash)

The escape character (\) preserves the literal meaning of the next character. You can't obtain a single backslash by quoting \ with double quotes. To obtain a backslash, enter \\ instead.

Double quotes

Enclosing characters and words in double quotes ("") preserves the literal meaning of all characters within double quotes, with the exception of the \ character. For example:

    "ab cd"

represents a single, five-character argument.

You can keep the literal meaning of a double quote with the \ character. For example:

    ab\"cd

represents the single, five-character argument ab"cd.

Builtin commands

The following commands are built into uesh. That is, uesh interprets and executes them internally.

cd

change working directory

cd [directory]

The cd utility changes the working directory of the current execution environment. If directory isn't specified, the value of the HOME environment variable becomes the new working directory. If restricted mode (-r) is set, you can't start the pathname with a double slash.

exec

execute a command and/or manipulate file descriptors

exec [command [argument...]]

The exec command opens, closes, or copies file descriptors as specified by any I/O redirections given as part of argument. If a command is specified, that command is spawned as a replacement for uesh. Any specified arguments are passed to the spawned process.

exit

cause uesh to exit

exit [n]

The exit command causes uesh to exit with the exit status specified by n. If n isn't specified, uesh exits with the status of the last command executed.

export

mark environment variables for export

export name[=word]...
export -p

The export command marks the specified names for export, which will cause them to be in the environment of subsequently executed commands. If you specify the -p option, the names and values of all exported variables are written to the standard output.

If restricted mode (-r) is set, you can't use this command.

Examples:

Invoke the script /etc/backup with uesh:

    esh /etc/backup

Environment variables:

You can use the following variables to modify uesh's environment:

HOME: The pathname of the user's home directory
LOGNAME: The user's login name.
PATH: The directory search path used by uesh for locating executable programs and uesh shell scripts. To change PATH, you must use the export command.
If PATH isn't in the existing environment when uesh is invoked, it is set to /bin:/usr/bin.
SHELL: The pathname of the user's preferred shell.
TERM: The terminal type.
TMPDIR: The pathname of a directory that can be used by utilities that need a place to create temporary files.
TZ: The timezone setting.

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