10-15-2012
Shell quoting rules for other languages programmers
I've seen so many times that programmers were confused about shell quoting and white spaces interpretation, that I decided to investigate that problem deeper. And my conclusion is that quoting in shells is
very different from other programming languages. Programmers who have bigger experience in C/Python/Java/PHP than in Shell should remember about two
unintuitive rules:
- everything in shell is a string, and one need to quote everything properly. Also when reading variables: "$X", not only storing X="hi there"
- shell will parse lines of code just one time, leaving unresolved nested variables and commands. In this case programmer need to explicitly use "eval" function.
I've written short article about this if anyone will be more curious you can find it under "white shell cofoh"
This User Gave Thanks to wyderkat For This Post:
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msh(1mh) msh(1mh)
Name
msh - MH shell
Syntax
msh [ -help ] [ -prompt string ] [ file ]
Description
The command is an interactive program that implements a subset of the normal MH commands operating on a single file in format. That is, is
used to read a file that contains a number of messages, as opposed to the standard MH style of reading a number of files, each file being a
separate message in a folder.
The chief advantage of is that, unlike the normal MH style, it allows a file to have more than one message in it. In addition, can be used
on other files, such as message archives which have been packed using
When invoked, reads the named file, and enters a command loop. You can type most of the normal MH commands. The syntax and semantics of
these commands typed to are identical to their MH counterparts. In cases where the nature of would be inconsistent with the way MH works
(for example, specifying a +folder with some commands), will duly inform you. The commands that currently supports are:
ali burst comp dist folder
forw inc mark mhmail msgchk
next packf pick prev refile
repl rmm scan send show
sortm whatnow whom
In addition, has a command which gives a brief overview of all the options. To terminate either type <CTRL/D>, or use the command. If the
file is writable and has been modified, then using will ask you if the file should be updated.
A redirection facility is supported by Commands may be followed by one of the following standard ULTRIX symbols:
| Open an interprocess channel; connect output to another ULTRIX command.
> Write output to file.
>> Append output to file.
If file starts with a tilde (~), then a C-shell-like expansion takes place. Note that commands are interpreted by
When parsing commands to the left of any redirection symbol, will honor the backslash () as the quote next-character symbol, and double
quotes (") as quote-word delimiters. All other input tokens are separated by white space (spaces and tabs).
You may wish to use an alternative profile for the commands that executes; see for details of the $MH environment variable.
Options
-help Prints a list of the valid options for this command.
-prompt string
Sets the prompt for If the string you specify includes white space, you must enclose it in double quotes ("). If you do not
specify this option, the default prompt is (msh).
The following defaults are used by
file defaults to
-prompt (msh)
Restrictions
The shell is not the C-shell, and a lot of the facilities provided by the latter are not present in the former. In particular, does not
support back-quoting, history substitutions, variable substitutions, or alias substitutions.
does not understand back-quoting. The only effective way to use inside is to always use the -seq select option. If you add the following
line to your will work equally well from both the shell and
pick: -seq select -list
There is a strict limit of messages per file in format which can handle. Usually, this limit is 1000 messages.
Profile Components
Path: To determine your Mail directory
Msg-Protect: To set protections when creating a new file
fileproc: Program to file messages
showproc: Program to show messages
Files
The user profile.
The system customization file.
See Also
csh(1), packf(1mh), sh(1), mh_profile(5mh)
msh(1mh)