# Declaring a variable, no space after equal sign
variable="Hello world."
# Using the variable
echo $variable
# print an expression
echo $(( 660 + 6 ))
# Builtin variables:
echo "Last program return value: $?"
echo "Script's PID: $$"
echo "Number of arguments: $#"
echo "Scripts arguments: $@"
echo "Scripts arguments separated in different variables: $1 $2..."
# Reading a value from input:
echo "What's your name?"
read name # no need to declare a new variable
echo Hello, $name!
# basic if structure
if [ $username -ne $USER ]
then
echo "Your name isn't your username"
else
echo "Your name is your username"
fi
# conditional execution
echo "Always executed" || echo "Only executed if first command fails"
echo "Always executed" && echo "Only executed if first command does NOT fail"
# use square brackets for multiple conditions
# To use && and || with if statements, you need multiple pairs of square brackets:
if [ $userName == "lucy666" ] && [ $age -eq 15 ]
then
echo "This will run if $userName is lucy666 AND $Age is 66."
fi
if [ $userName == "bastard21" ] || [ $userName == "evilclown" ]
then
echo "This will run if $userName is bastard21 OR evilclown."
fi
case "$myVar" in
# List patterns for the conditions you want to meet
0) echo "There is a zero.";;
1) echo "There is a one.";;
*) echo "It is not null.";;
esac
# print variable 3 times
for myVar in {1..3}
do
echo "$myVar"
done
# Or write it the "traditional for loop" way:
for ((i=1; i <= 3; i++))
do
echo $i
done
# can be used to act on files..
# This will run the command 'cat' on file1 and file2
for myVar in file1 file2
do
cat "$myVar"
done
# output from a command
# This will cat the output from ls command.
for x in $(ls)
do
cat "$x"
done
# while loop:
while [ true ]
do
echo "loop body..."
break
done
# define a function
function foo ()
{
echo "Arguments work just like script arguments: $@"
echo "And: $1 $2..."
echo "This is a function"
return 0
}
# alternatively, you can also just declare without the function keyword
bar ()
{
echo "Another way to declare functions!"
return 0
}
# Calling you function
foo "My name is" $name
# find files that start with the word "text"
find -name "text"
# find only directories
find /var/log -name "syslog" -type d
# find only files
find -type f
grep <someText> <fileName> = search for text in file
-i = case insensitive
-I = exclude binary files
grep -E ^<text> <fileName> = search start of lines with the word text
sort <fileName> = sort alphabetically
sort -o <file> <outputFile> = write result to a file
sort -r <fileName> = sort in reverse
sort -R <fileName> = sort randomly
wc <fileName> = word count
options:
-l (lines), -w (words), -c (byte size), -m (number of characters)
cut = cut a part of a file
options:
-c --> Ex, cut -c 2-5 names.txt
(cut the characters 2 to 5 of each line)
-d (delimiter) (-d & -f good for .csv files)
-f (# of field to cut)