LFS101x.2 Introduction to Linux - Notes

shell-notes

#!/bin/bash

# Declaring functions
function display() {
  echo "Hello" $1 "!"
}

# ./my_script.sh param1 param2
# $0 (script name)
# $1 .. $n (nth parameter)
# $* (all parameters)
# $# (number of arguments)

# Using variables
var="something"
echo $var

# Read user input
echo "Please enter your name:"
read name
display $name  # call to function

# Testing for files
if [[ -f /etc/passwd ]]
then
  echo "The file exists!"
elif [[ -f /etc/other ]]
then
  echo "Other file exists"
else
  echo "The file doesn't exist"
fi

# Operands:
# &&, ||, ! (not)

# Testing for files:
# -----------------
# -e (file exists)
# -d (file is directory)
# -f (file is regular file)
# -s (file has non-zero size)
# -r (file is readable)
# -w (file is writable)
# -x (file is executable)

# Numerical tests:
# ----------------
# -eq, ne, gt, lt, ge, le

echo $((2 + 1))

echo $? # status of the last command

string="alejandro"

len=${#string} # Saves the length of string1 in the variable len
halfLength=${string:0:4}

echo $len
echo $halfLength

set -x # start debugging

read NUM

case $NUM in
  1) echo "one";;
  2) echo "two";;
  3) var=$NUM; exit;;
  *) echo "other number";;
esac

set +x # stop debugging

TEMP=$(mktemp /tmp/tempfile.XXXXX) # create temporary file 
# add option -d to create a folder

# command: test

# exit # exit status of the last command, equivalent to 
# command below
# exit $?