12-06-2000
me2unix does a great job of stating the main difference between C program and shell programs.
C is a compiled and executed language.
Shells are C programs written to interpret commands without compiling them.
The same holds true for PERL, PYTHON, PHP and other C programs that are compiled.
So, just look at SHELLs as C programs that have built-in functions and the ability to call other C programs. If you need a C program feature in a SHELL, you simply write a C program, compile it and execute it within the SHELL environment, as me2unix explains.
In fact, entire programs are often written via SHELLS as folks familiar with PHP, PERL, etc. Even the Java Virtual Machine (JVM) is a 'kind of SHELL' program if you think about it. The JVM is just a 'special class of shell'.
This was a good question by the thread starter and a good answer by m2unix.
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NAME
smrsh - restricted shell for sendmail
SYNOPSIS
smrsh -c command
DESCRIPTION
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sharply limits commands that can be run using the |program syntax of sendmail. This improves overall system security. smrsh limits the set
of programs that a programmer can execute, even if sendmail runs a program without going through an alias or forward file.
Briefly, smrsh limits programs to be in the directory /var/adm/sm.bin, allowing system administrators to choose the set of acceptable com-
mands. It also rejects any commands with the characters: ,, <, >, |, ;, &, $,
(<RETURN>), or
(<NEWLINE>) on the command line to pre-
vent end run attacks.
Initial pathnames on programs are stripped, so forwarding to /usr/ucb/vacation, /usr/bin/vacation, /home/server/mydir/bin/vacation, and
vacation all actually forward to/var/adm/sm.bin/vacation.
System administrators should be conservative about populating /var/adm/sm.bin. Reasonable additions are utilities such as vacation(1) and
procmail. Never include any shell or shell-like program (for example, perl) in the sm.bin directory. This does not restrict the use of
shell or perl scrips in the sm.bin directory (using the #! syntax); it simply disallows the execution of arbitrary programs.
OPTIONS
The following options are supported:
-c command
Where command is a valid command, executes command.
FILES
/var/adm/sm.bin directory for restricted programs
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsr, SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO
sendmail(1M), , attributes(5)
SunOS 5.10 6 Nov 1998 smrsh(1M)