CSC231 nasmld script

--D. Thiebaut 09:18, 7 November 2012 (EST)
revised --D. Thiebaut (talk) 09:06, 30 September 2015 (EDT)

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This page presents a super fast introduction to writing bash scripts to assemble and link programs.

Preparation and Mini Lab

• Creating a bash script is a very simple process:

1. use emacs to create a text file (the same as an assembly file). Give it a catchy name. For example myScript.sh (.sh is a common extension for scripts).
2. write this as the first line of the script:

  #! /bin/bash

1. add comments that start with the # character. Document the script with a header.
2. add Linux commands, one per text line.
3. save your file
4. and make it executable:

  chmod a+x myScript.sh

(make sure the file name is the one you created with emacs!)

1. and you're done!
2. You can now run your script as follows:

  ./myScript.sh

Understanding Command-Line Parameters

Step 1

• Create the following script, called script1.sh:

#! /bin/bash
# script1.sh
# your name
# demo script

echo "program name =  $0"
echo "first parameter = $1"
echo "second parameter = $2"

• make your script executable and run it with a few parameters:

 chmod a+x 
 ./script1.sh
 ./script1.sh hello beautiful world!
 ./script1.sh 1 + 2 = 3

• You should now understand what $0, $1, and so on refer to in a bash script.

Step 2

• Modify your script and add a few lines:

#! /bin/bash
# script1.sh
# your name
# demo script

echo "Your input line is $@"
echo "You have entered $# parameters"
echo "program name =  $0"
echo "first parameter = $1"
echo "second parameter = $2"

Step 3: testing if the # of parameters is correct

• Another modification: we check to see if $1, the first parameter on the command line, exists. If it doesn't, then we display some syntax/usage information for the user, and the script stops. You may want to look at this page on how to test various quantities in bash.

#! /bin/bash
# script1.sh
# your name
# an example script that makes sure there's 1 parameter before displaying
# what is found on the command line.


# display syntax if user forgets Parameter 1.  We test is the length of parameter 1 
# is 0. (-n is true if length is non zero, so ! -n is true if the length is 0)
if [ ! -n "$1" ]; then   
  echo "Usage: `basename $0` parameter1"
  exit 1
fi  

# display various quantities referring to the command line.
echo "your input line is $@"
echo "you have entered $# parameters"
echo "program name =  $0"
echo "first parameter = $1"
echo "second parameter = $2"

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An Assemble/Link Script: Version 1

#! /bin/bash
# nasmld
# D. Thiebaut
# assembles and links an assembly program for 
# a Pentium processor running Linux
# To create the script, edit with your favorite text editor,
# save to current directory or to ~/bin, and make executable:
# 
#     chmod +x nasmld
#
set -e   # stop on error

filename=$(basename "$1")   # remove the path in front of the file name
filename="${filename%.*}"   # remove the extension from the file name

nasm -f elf -F stabs $filename.asm
ld -o $filename -melf_i386 $filename.o
rm $filename.o
./$filename

A More Sophisticated Assemble/Link Script: Version 2

This version stops and gives an error message if nasm or ld return an error.

#! /bin/bash
# nasmld
# D. Thiebaut
# assembles and links an assembly program for 
# a Pentium processor running Linux.
# To create the script, edit with your favorite text editor,
# save to current directory or to ~/bin, and make executable:
# 
#     chmod +x nasmld
#

# display syntax if user forgets
if [ ! -n "$1" ]
then
  echo "Usage: `basename $0` progName"
  exit 1
fi  

# remove the ".asm" part of the filename
filename=$(basename "$1")    # remove path
filename="${filename%.*}"    # remove extension

# assemble and generate a listing (optional)
nasm -f elf -F stabs $filename.asm -l $filename.lst

# if we get errors, stop
if [ "$?" -ne "0" ]; then
    echo "*** Nasm ERROR! ***"
    exit
fi

# link
ld -melf_i386 -o $filename $filename.o

# if we get errors, stop
if [ "$?" -ne "0" ]; then
    echo "Link ERROR! ***"
    exit
fi

# no errors, run the program!
rm $filename.o
./$filename

Usage

If you have a program, say HelloWorld.asm, and want to assemble, link and run it, simply type:

  nasmld  HelloWorld.asm

at the command line, or, if that doesn't work:

  ./nasmld HelloWorld.asm