Linux2

Leveraging the power of the Linux command line

Getting the content for this practical

The necessary files for this practical are hosted in a version control system. To obtain them, just type the following command:

$ svn export http://source.ggy.bris.ac.uk/subversion-open/linux2/trunk linux2

This will fetch all necessary files and put them in a folder called linux2/. Ignore the cryptic syntax so far, an introduction to version control using subversion (svn) will be given later on.

Output redirection

In the Linux1 practical, we have discovered a few Linux commands. Some of these commands use input from the keyboard (standard input) and output data to the screen (standard output). It is possible to (a) redirect input and output and (b) link commands together to perform complex actions.

Redirecting standard input and output

The diff command outputs to the screen.

$ diff file1 file2

$ diff file1 file2 > diff12.txt
$ diff file2 file3 > diff23.txt

$ cat diff12.txt diff23.txt > diff.txt

$ diff file1 file2 > diff.txt
$ diff file2 file3 >> diff.txt

It is also possible to redirect the input. For instance consider the following

Pipelines

pipes between simple commands

ls -l | more

diff file1 file2 | tail

grep -i scene | wc

Automating things

"batch files"

$ cd example2

convert is a small utility from the program Imagemagick which allows the manipulation of images at the command line. For instance, to resize an image to 2000 pixels max and rename it, you could use:

$ convert image-large.jpg -resize 2000 image-2000.jpg

Now let's say

#!/bin/bash

echo "Create thumbnails."
convert image-large.jpg -resize 2000 image-2000.jpg
convert image-large.jpg -resize 1000 image-1000.jpg
convert image-large.jpg -resize 500 image-500.jpg
convert image-large.jpg -resize 100 image-100.jpg
convert image-large.jpg -resize 10 image-10.jpg

echo "Move thumbnails."
mkdir thumbnails
mv image-*0.jpg thumbnails/

echo "Compress thumbnails."
zip -r thumbnails thumbnails

echo "Clean up."
rm -rf thumbnails

echo "All done."

Launching, monitoring and controlling jobs

Background, bg, jobs, fg, nohup, top, kill

Environment Variables

SHELL PWD PATH (LD_LIBRARY_PATH)

Uploaded example scripts for:

• Environment Variables
• Conditionals
• For loops
• Functions
• Arithmetic

Text Processing

sed, awk.