Cheat sheet (bash script)

bash_cheat_sheet.sh

#!/bin/bash

# Comments are like that
# First line is the shebang with #, !, then path to the executable (meaning it can be /bin/python)

#####################
## STATEMENTS
#####################

# One Statement per line
foo="Bar"
echo $foo

# Chained Statements on same line
foo="Bar";echo $foo


#####################
## VARIABLES
#####################

# Variable assignment : using '=' (no spaces around)
some_variable="Some string Value"
other_variable=12

variable_from_command_output=`uname -a`
# OR
variable_from_command_output=$(uname -a)

# Using variables by prefixing them with '$'
echo $variable_from_command_output

# concatenate
some_other=$some_variable$other_variable
# $some_other equals "Some string Value12"

# format string
format_other="Twelve is "$other_variable
format_other="Twelve is ${other_variable}"

# Built-in Variables
# $0 contains the call to the script, as it is typed
echo "Command line is '${0}'"

# $1 $2 $3 ... are the arguments of the script, beware, if they are not present they will be empty
echo "Arguments are '$1' '$2' '$3'"

# $# contains the number of arguments
echo "You passed $# arugment(s)"


####################################
## READING FILES
####################################

while read -r line; do
    echo "$line"
done < filename.txt


####################################
## STRING SEARCH/REPLACE
####################################

searchString="I love Suzy and Mary"
search="Suzi"
replace="Sara"
echo "${searchString/"$search"/"$replace"}"
# prints 'I love Sara and Mary'

#To replace all occurrences, use ${parameter//pattern/string}:
message='The secret code is 12345'
echo "${message//[0-9]/X}"
# prints 'The secret code is XXXXX'


####################################
## UTILITIES
####################################

script_absolute_directory=$(dirname $(readlink -f $0))
echo "Current Script absolute directory is $script_absolute_directory"