Embedded shell (QNX Neutrino)
esh [-c command] [-irv] [script_file]
QNX Neutrino
Restricted operations include running executables that start with a slash, exporting variables, and reattaching standard input, output and error to another device. For more information, see the sections “Command-line format” and “Builtin commands.”
The esh utility provides a subset of the functionality found in the standard shell, /bin/sh. You should find esh 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.
Command-line format
In esh, command lines take this form:
command arg1 arg2 ... [redir-op file] [&]
where:
| 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 esh 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
You use most commands for manipulating files in one way or another. As such, esh has a filename “shorthand” (consisting of *, ?, [, and ]) that you can use to specify the files that a command is to operate on. This shorthand is the same used by the standard shell. For more information, see “Filename patterns” in ksh.
Quoting
The following characters have a special meaning in esh:
& \ " * ? [ 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 esh (that is, esh interprets and executes them internally):
. (dot) command
. file
The . (dot) command reads and executes the commands from file within the current environment. The search path contained in the environment variable PATH is used to find the directory containing file. This command doesn't require that file be executable.
alias command
alias [name=value]...
Without arguments, alias lists all aliases and their values. If only the name is specified, its value is listed. Any name specified with a value defines an alias.
Alias expansion occurs when the first word of a statement is a defined alias, except when that alias is already being expanded.
List all aliases:
alias
Remove an alias:
alias name=
cd command
cd [directory]
Change 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.
emount command (QNX Momentics 6.3.0 Service Pack 2 or later)
emount special directory [fs_type]
Mount a special device. The arguments are:
| type: | Filesystem or manager: |
|---|---|
| cd | fs-udf.so |
| cifs | fs-cifs |
| dos | fs-dos.so |
| mac | fs-mac.so |
| nfs | fs-nfs2, fs-nfs3 |
| nt | fs-nt.so |
| qnx6 | fs-qnx6.so (Power-Safe filesystem) |
| udf | fs-udf.so |
The default is qnx6.
ewaitfor command (QNX Momentics 6.3.0 Service Pack 2 or later)
ewaitfor path [max_seconds [delay]]
Wait until the given path exists. The arguments are:
exec command
exec [command [argument...]]
Execute a command and/or manipulate file descriptors.
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 esh. Any specified arguments are passed to the spawned process.
If esh is operating in restricted mode (-r), you can't use the exec command to run a command whose path starts with a slash.
exit command
exit [n]
Cause esh to exit with the exit status specified by n. If n isn't specified, esh exits with the status of the last command executed.
export command
export name[=word]... export -p
Mark environment variables for export. This makes them 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.
kill command
kill pid
Set a SIGTERM on the process with process ID pid.
reopen command
reopen [device]
Close standard input, standard output, and standard error and attach them to the specified device. This command is often used in startup scripts. If you don't specify a device, /dev/con1 is used.
If restricted mode (-r) is set, you can't use this command.
set command
set -v
Enable verbose mode; all commands are echoed to the standard output before they're executed.
unset command
unset variable
Unset the specified variable. If restricted mode (-r) is set, you can't use this command.
Invoke a subshell:
esh
Invoke a subshell with a script file:
esh /etc/backup
Run the following command and exit:
esh -c "ls /bin"
If PATH isn't in the existing environment when esh is invoked, it is set to /bin:/usr/bin. For more information on setting PATH, see “Setting PATH and LD_LIBRARY_PATH” in the Configuring Your Environment chapter of the QNX Neutrino User's Guide.
The current version of esh strips out single quotes ('), which means that many common uses of commands such as find fail.