Tutorial: A bit of Bash
--D. Thiebaut (talk) 11:03, 26 November 2013 (EST)
A quick review of some useful Bash commands that can be used on the command line, or that can be included in bash scripts
Creating a bash script
- first line should contain name of bash shell
#! /bin/bash
- make the script executable
chmod +x scriptname
Variables
- Declaration
file="hello.txt" file=`ls -1 *.txt | head -1` # get the first .txt file in the directory
- In expressions: put a $ in front of it!
URL="http://cs.smith.edu/dftwiki/images/" file="toto.png" pathFile=$URL$file file="alpha" pathFile=$URL${file}.png # add braces if string needs to be concatenated to variable
Script Parameters
- assume doit.sh is a script and it is called as follows: doit.sh 8 2000 50
- To get the arguments inside the script:
NP=$1 # will get 8 N=$2 # will get 2000 M=$3 # will get 50
- To test if the number of parameters is 3 inside the script:
if [ "$#" -ne 3 ]; then echo "syntax: doit.sh NP N M" exit fi