CSC231 nasmld script
--D. Thiebaut 09:18, 7 November 2012 (EST)
revised --D. Thiebaut (talk) 09:06, 30 September 2015 (EDT)
Contents
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:
- 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).
- write this as the first line of the script:
#! /bin/bash
- add comments that start with the # character. Document the script with a header.
- add Linux commands, one per text line.
- save your file
- and make it executable:
chmod a+x myScript.sh
- (make sure the file name is the one you created with emacs!)
- and you're done!
- 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 = $2"
An Assemble/Link Script: Version 1
#! /bin/bash # nasmld # D. Thiebaut # assembles and links an assembly program for # a Pentium processor running Linux # To create the script, edit with your favorite text editor, # save to current directory or to ~/bin, and make executable: # # chmod +x nasmld # set -e # stop on error filename=$(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