Scripting

• Scripting
  • Fundamentals
  • If Statements
    • Conditions
  • Case Statements
  • Loops
    • For Loops
    • While Loops
    • Until Loops
  • Functions

Fundamentals

Shebang (first line of file) for shell (.sh) files: #!/bin/sh or #!/bin/bash

Shell arguments: $1, $2 … $9; $@ (all arguments)

If Statements

if condition1; then
    command1a
    command1b
elif condition2; then
    command2
else
    command3
fi

Conditions

test $# -ne 2 or [ $# -ne 2 ] (spaces are required!)

Case Statements

echo -n "yes/no? "
read answer
case $answer in
    y | yes ) echo "yes";;
    n | no ) echo "no";;
    *) echo "invalid input";;
esac

Loops

For Loops

for i in a b c; do
  echo $i
done

IFS=$'\n' # Internal Field Separator (needed to allow spaces in filenames)
for file in $*; do
  cp "$file" "$file.bak"
done

While Loops

i=1
while [ $i -le 5 ]; do 
  echo $i; i=$(($i+1))
done

Until Loops

i=1
until [ $i -gt 5 ]; do
  echo $i; i=$(($i+1))
done

Functions

function myFunc {
  echo "Hello World, $1!"
}
myfunc "Linux"

myFunc() {
  echo "Hello World, $1!"
}
myfunc "Linux"

greet() {
  echo "Hello $1 $2!"
}
greet "John" "Doe"