Executing Scripts - Paiet/Tech-Journal-for-Everything GitHub Wiki

• ​Scripts
  • A collection of commands run in order
  • Can be static, or accepts modifiers
• Executing a script
  • Example 1: bash myscript.sh
    • Interpreter calls the script
  • Example 2: ./myscript.sh
    • Interpreter should be defined on line 1
    • #! /bin/bash
    • Must have execute permissions
• Demonstration
  1. vi ~/myscript.sh
  2. `echo "Test output"
  3. ~/myscript.sh
     • Fails due to missing +x
  4. bash myscript.sh
     • Success
  5. chmod +x ~/myscript.sh
  6. ~/myscript.sh
     • Success, but missing interpreter may be an issue
• Variables
  • Many scripts accept input to change their behavior
  • Variables can be populated in the script
  • Variables can be provided via the command line
  • Arguments
    • Variables are populated from the command line
    • Unnamed become $1, $2, etc
    • Can be named
      • NAME="Nicholas"

Basic Variables

#! /bin/bash
# Syntax: myscript.sh <firstname> <lastname>
HOSTNAME=`hostname`
echo "Firstname: $1"
echo "Lastname: $2"
echo "Full Name: $1 $2"
echo "Shell: $SHELL"
echo "Hostname: $HOSTNAME"
echo "The date is `date`"

Accepting Input

#! /bin/bash
# Syntax: myscript.sh
HOSTNAME=`hostname`
read -p "Enter Firstname: " FNAME
read -p "Enter Lastname: " LNAME
FULLNAME="$FNAME $LNAME"
echo "Firstname: $FNAME"
echo "Lastname: $LNAME"
echo "Full Name: $FULLNAME"
echo "Shell: $SHELL"
echo "Hostname: $HOSTNAME"
echo "The date is `date`"

Performing Arithmetic

NUMBER1=36
NUMBER2=2
let RESULT1=$NUMBER1/$NUMBER2; echo "$NUMBER1/$NUMBER2=$RESULT1"
RESULT2=`expr $NUMBER1 / $NUMBER2`; echo "$NUMBER1/$NUMBER2=$RESULT2"
RESULT3=`echo "$NUMBER1 / $NUMBER2" | bc`; echo "$NUMBER1/$NUMBER2=$RESULT3"