OPS435 Lecture 4 - Bash

• Writing a script
• Receiving parameters
• Return codes
• true and false commands
• Program control:
  • if
  • test, [
  • [[
• Parameter expansion examples
  • echo $1
  • echo ${11}
• Input from the user
  • read command

In-class examples

runme.sh:

#!/bin/bash

echo "First parameter was $1"
echo Second: $2
echo 'Third parameter: ' $3
echo "Fourth parameter was $4"

divide.sh:

#!/bin/bash

if [[ $# -lt 1 ]]
then
  echo "Not enough parameters"
  exit
fi

echo $(( $1 / 2 ))

stringtest.sh:

#!/bin/bash

COMPARETO=hello
COMPARETO="hello"
COMPARETO='hello'

if [ x$1 = x$COMPARETO ]
then
  echo "You guessed the string"
else
  echo "Guess again"
fi

testcommand.sh:

#!/bin/bash

if ls /etc/linuxmint > /dev/null 2> /dev/null
then
  echo "Correct distribution"
else
  echo "Please run this script on linux mint"
  exit
fi

FILETYPE=`file -b /etc/linuxmint`
#if [ "$FILETYPE" = "directory " ]
if test "$FILETYPE" = "directory "
then
  echo "It's a directory as I expected"
else
  echo "It's not a directory"
  exit
fi

ask.sh:

#!/bin/bash

echo "Script started"
echo "Please choose one of the following files: "
cd /var/log
ls syslog*

echo -n "Your choice: "
read CHOSENNAME

echo $CHOSENNAME