UNIX Bourne Shell Programming

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7. VAX DCL TO UNIX SHELL SCRIPT CONVERSION.

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7.4 Command Structure and File Naming Conventions

VMS is not case-sensitive in its interpretation of commands. It
doesn't distinguish between upper and lower case characters. This
is not true in UNIX, however. Commands must be entered in lower
case characters only. The Shell will not understand characters that
are in uppercase.

Filenames are also case sensitive in UNIX. The file named
MYFILE.DAT and the file myfile.dat refer to different files. One
advantage of this is that you can have a much larger variety of
filenames with fewer characters. Especially good if you don't like
to type.

This also has advantage over the filename conventions used by VMS.
Directories and subdirectories are pointer files in both operating
systems. When a subdirectory is created in VMS it is given the
extension name .DIR automatically. UNIX files on the other hand do
not distinguish between ordinary files and directories. Many VMS
users have adopted a practice of naming new subdirectories in UNIX
with all capital letters or the first letter being capitalized.
This is not, however, standard UNIX practice.

VMS Sample Session:

$CREATE/DIRECTORY [.TEST]
$DIRECTORY

UNIX Shell Sample Session:

$mkdir Test
$ls Test

It is possible in UNIX to maintain the same filename conventions
that you used in VMS. The period (.) is a legal character in a UNIX
filename. Some VMS users like to continue the practice of naming
files using the same . extensions from VMS. Problems occur when
default extensions are different between the two systems. For
example, object files use the extension .OBJ in VMS but .o in UNIX.
Another example is FORTRAN source code in UNIX the extension is .f
and VMS uses .FOR. Note that .o and .f are UNIX conventions to
facilitate file recognition and that UNIX commands do not assume
file extensions as VMS does.
Here is a list of commonly used extensions for both operating
systems.

VMS UNIX Definition

.OLB .a Library

.BAS .bas BASIC Source Code

.C .c C Source Code

.FOR .f FORTRAN Source Code
.h C header files
.l lex program

.OBJ .o Object Code

.PAS .p PASCAL Source Code
.s Symbolic Assembly Code
.y yacc program

.EXE a.out Executable Image

.ADA ADA Source Code
.B32 BLISS-32 Source Code
.CLD Command description file
.COB Cobol Source Code
.COM Commands for the language interpreter
.DAT Data file
.DIS Distribution list file for MAIL
.DIR Directory file
.EDT Startup command file for EDT editor
.DOC Documentation
.HLP Input source files for HELP Library
.JOU Journal file created by EDT
.LIS Listing of text
.LOG Batch job output file
.MAI MAIL message file
.MAR VAX Macro source code
.SYS System Image
.TMP Temporary file

7.5 File Management Commands

This is a table of the more commonly used file management commands.
Some of these commands have been covered elsewhere in this manual.
The on-line manual command (man) can be used to get detailed
information about any UNIX command.

UNIX VMS Purpose
Command equivalent

ar LIBRARY Archive files

awk TPU Pattern matching utility

cat TYPE/APPEND Catenates and prints to
terminal

cd SET DEFAULT Change working directory

chgrp SET FILE Change group ownership

chmod SET PROTECTION Changes protection

cmp DIFFERENCE Compares two files and reports
first difference found

cp COPY Create a new copy

find DIRECTORY Locates within a directory
structure

ftp COPY Transfer to/from remote node

grep SEARCH Finds a string

ln ASSIGN Create a symbolic link

ls DIRECTORY List contents of a directory

merge MERGE Merge files

mkdir CREATE/DIR Make a directory

mv RENAME Moves or renames files

od DUMP Octal, decimal, hex, ASCII
dump

pr PRINT/HEAD Prints files

pwd SHOW DEFAULT Working directory name

rm DELETE Removes or deletes files

rmdir DELETE Removes a directory file

sort SORT Sorts by a key

tail EDIT/READ Outputs last part of file

tar BACKUP Tape archive

touch CREATE Updates file characteristics
or creates null file

tr EDIT Translates characters

7.6 Metacharacters

Characters that have special meanings to the Shell are known as
metacharacters. Users should avoid using these characters in
filenames as results might be unpredictable. We have already seen
several metacharacters, for example, vertical bar (|), or the
greater than (>) or less than (<). The function of metacharacters
can be different depending on whether the Shell or a UNIX tool
interprets the character. The following is a list of UNIX special
characters and their VMS equivalent.

UNIX Function VMS equivalent
Char

& Perform command in Background
= Assignment operator =
; Command separator
\ Continuation of command line -
\m Literal translation of metacharacter m "m
' Turn off special meaning "
` Process immediately @ & run
" Group characters into a single argument "
# Comment follows !
* Wildcard filename substitution *
? Wildcard filename substitution single character %
$ Argument substitution follows '
$# Argument count
$$ Process id F$GETJPI("PID")
$? Exit status $STATUS
$< Read one line from standard input INQUIRE, READ
. Current directory []
[] Selective filename substitution

Note: Metacharacters unique to the C-Shell have not been included
in this list to reduce confusion. Check C-Shell documentation for
a complete list.

7.7 Wildcards: Are They Really Wild?

UNIX wildcards extend the features found with wildcards in VMS.
The following table shows how UNIX expands wildcard definitions:

UNIX example Meaning

* # All files in the current directory and one
level below

. # Files in the current directory

*.* # All files that contain a period in the filename |

*.com # All files in the current directory that
end in .com

?.com # All files in the current directory that
end in .com and have one character
preceding the period

name[xyz] # All files in the current directory, namex,
namey, or namez

name[a-z] # All files in the current directory namea
through namez

name[a-z4] # All files in the current directory, namea
through namez and name4

There are no absolute rules concerning the use of wildcards. The
output produced by the wildcard expansion process is command
dependent. For instance, the ls * command will list files in the
current directory and the files in the directory in the next lower
level as well. The wc * (word count) command will produce output
for the files in the current directory only. Thus as you can see
commands vary in how wildcards are expanded.

Users and programmers can use wildcards in a similar way to the
method of using wildcards on the VAX. UNIX will interpret *.com to
mean any file in the current directory that ends in .com even
though the extension has no meaning in UNIX.

7.8 Summary

The VMS and UNIX operating systems are similar in some respects.
The VMS user must recognize that there are some fundamental
differences.

UNIX allows multiple processes and the user must learn to manage
these processes. VMS usually manages a single process which
processes commands in sequence.

UNIX has a different command syntax. UNIX commands are already
short and cannot be abbreviated like VMS commands. UNIX commands
do not lend themselves easily to describe their function. For
example, TYPE seems to describe the function better than cat in
UNIX. Single letter options modify UNIX commands in a manner
similar to VMS command qualifiers.

UNIX has a different file and directory structure. You can address
any file irrespective of the physical device using the absolute or
relative pathname.

UNIX has metacharacters which have special functions when
interpreted by the Shell.

Workshop 7

This workshop will reinforce your understanding of the ideas
presented in all the previous chapters. Login to the Multimax using
the username and password given to you by the instructor. Each
student is to complete the entire workshop.

DESK EXERCISES

1. Convert the DCL command file found on the next page
to BourneShell and run it.

Helpful?? Hints:

What does the VMS DCL command file do?

Does UNIX Shell have a similar function?

What does the UNIX command cut do?

What does the UNIX command date do?

Can this script be converted one line at a time?

2. Not all functions, especially calls to library
functions, that exist in VMS have an equivalent call in
UNIX Shell. An example of this is F$ELEMENT in VMS.
Write a BourneShell script that will do the same job as
F$ELEMENT and test it.

If time remains and you want a further challenge:

3. Write a user interface to add and delete records to the
phone.lis database. Query the user in a user friendly
manner and check to see if the name is already in the
database prior to adding it.

That's all for this workshop. If you didn't finish
because of time, that's OK, as long as you understand
the process needed to do conversions.

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