Shell Scripting

script.sh

#!/bin/bash
echo "Scripting is fun!"

$ chmod 755 script.sh
$ ./script.sh
Scripting is fun!

#!/usr/bin/python
print "This is a python script!"

Variables

VARIABEL_NAME="bash"
echo "I like the $VARIABLE_NAME shell."
echo "I like the ${VARIABLE_NAME} shell."

Assign a command output to a variable

#!/bin/bash
SERVER_NAME=$(hostname)
echo "You are running this script on ${SERVER_NAME}."

Variable Names

Letters, digits, underscores

Tests

[ condition-to-test-for]
[ -e /etc/passwd ]

-d	True, if file is a directory
-e	file exists
-f	exists and is a regular file
-r	file is readable to you
-s	file exists and is not empty
-w	exists and is writeable to you
-x	exists and is executable by you

arg1 -eq arg2	arg1 = arg2
arg1 -ne arg2	arg1 != arg2
arg1 -lt arg2	arg1 < arg2
arg1 -le arg2	arg1 <= arg2
arg1 -gt arg2	arg1 > arg2
arg1 -ge arg2	arg1 >= arg2

If statement

if [ condition-is-true ]
then
  command 1
  command 2
else
 command 3
fi

For loop

for VARIABLE_NAME in ITEM_1 ITEM_N
do
  command 1
  command 2
done

#!/bin/bash
COLORS="red green blue"

for COLOR in $COLORS
do
  echo "COLOR: $COLOR"
done

#!/bin/bash
PICTURES=$(ls *jpg)
DATE=$(date + %F)

for PICTURE in $PICTURES
do
  echo "Renaming ${PICTURE} to ${DATE}-${PICTURE}"
  mv ${PCITURE} ${DATE}-${PICTURE}
done

Postitional Parameters

$ script.sh parameter1 parameter2 parameter3

$0:"script.sh"
$1:"parameter1"
$2:"parameter2"
$3:"parameter3"

n Parameters

echo "executing script: $0"
for USER in $@
do
  echo "Archiving user: $USER"
  # Lock the account
  passwd -l $USER
  # Create an archive
  tar cf /archives/${USER}.tar.gz /home/${UESR}
done

User Input (STDIN)
read -p "PROMPT" VARIABLE