Bash is a great way to automate tasks and make your life easier as both a developer or an operator.
This project contains a few samples, tricks and stuff I can never remember :-)
In the samples folder of this repo you will find some of these snippets as indivual scripts.
These samples assuming the scripts are running bash. Add this to the top of the file to ensure that is the case
#!/bin/bash
Sometimes you want to run something and then test if the response contains a certain value.
Here is an example. The 'cf' command line interface is used to talk to Cloud Foundry. In this example we are testing the output of that command to check if an particular application is running in Cloud Foundry. We are terminating the script if the application is not here, but we also could take this opportunity to install it.
OUTPUT="$(cf events spring-music)"
if [[ $OUTPUT == *"App spring not found"* ]]; then
echo "The application does not exist, terminating the program"
exit 1;
fi
An example of IF/Then.
if [ "$greeting" == "hello" ]; then
echo "Hi!"
else
echo "What...no hello?"
fi
In this snippet we are prompting the user for a value, and then check to ensure it was not blank.
echo 'Please supply a non-blank value?'
read VALUE
if [ -z "$VALUE" ]; then
echo "I said 'non-blank'"
else
echo "You said: $VALUE"
fi
echo 'Done!'
Its often handy to know where in the file system a script is running. This command will do the trick.
export START_DIRECTORY=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
There are times you might wish to ensure a certain number of arguements.
if [ "$#" -ne 3 ]; then
echo "There needs to be at least 3 args"
fi
If a script needs to be have arguements passed in for it to work, you can add logic like this in the beginning of the script to stop execution if no arguements are specified.
if [ $# -eq 0 ]; then
echo "Usage: startSite.sh <names of serviceFile>";
echo "Hint: servicesToManageDev.txt, servicesToManageQA.txt, servicesToManageProduction.txt";
echo "Program terminating ...";
exit 1;
fi
echo "Are good to continue? (Type 'Y' to proceed)"
read CONFIRMATION
if [ "$CONFIRMATION" != "Y" ]; then
echo "Terminating the program"
exit 0;
fi
The following checks if a file exists.
#!/bin/bash
if [ -e smoketest.txt ]
then
echo "We have a smoketest file. Yipeee"
else
echo "There is no smoketest file! Boooooooooo"
fi
Sometimes so many arguements are passed into a script, it makes more sense to construct a properties file. In this example we have several row, with each row consisting of arguments seperated by spaces. Here is how values can be read from a file. Note: NAMES[i] contains the args in their respective positions.
Property File:
somethingcool option1 option2 option3
anothercoolthing option1 option2 option3
Script to read the property file above:
while read line
do
IFS=':' read -ra NAMES <<< "$line"
echo "${NAMES[1]}" "${NAMES[0]}" "${NAMES[2]}"
done < <(grep . "$START_DIRECTORY/$CONFIG_FILE")
Its handy to give a list of options, collect what the user wants and then perform a task based on their selection. The following is a script I like to use to SSH into different machines.
echo "++++++++++++++++"
echo "Which Server?"
echo "++++++++++++++++"
echo "1: QA"
echo "2: Jenkins"
echo "3: Production"
echo "4: Production Eureka"
echo "5: Data Server"
echo "6: Artifactory"
echo "---------------"
read option
if [[ ("$option" -eq "1") ]]; then
echo "SSHing into the QA Server"
ssh -i xxxxx.pem [email protected]
fi
if [[ ("$option" -eq "2") ]]; then
echo "SSHing into the Jenkins Server"
ssh -i xxxxx.pem [email protected]
fi
if [[ ("$option" -eq "3") ]]; then
echo "SSHing into the Production Server"
ssh -i xxxxx.pem [email protected]
fi
if [[ ("$option" -eq "4") ]]; then
echo "SSHing into the Production Eureka Server"
ssh -i xxxxx.pem [email protected]
fi
if [[ ("$option" -eq "5") ]]; then
echo "SSHing into the Data Server"
ssh -i xxxxx.pem [email protected]
fi
if [[ ("$option" -eq "6") ]]; then
echo "SSHing into Artifactory"
ssh -i xxxxx.pem [email protected]
fi
scp target/CoolBootApp-0.0.1-SNAPSHOT.jar [email protected]:/path-to-folder
cat /etc/*-release
if [ "$EUID" -ne 0 ]
then echo "Please run as root"
exit
fi
if [ $? -eq 0 ]; then
echo 'GREAT!'
else
echo 'Houston we have a problem'
fi
if [[ -z $(docker ps -q -f name=rabbit) ]]; then
echo 'Starting the Rabbit Docker image'
sudo docker start rabbitmq
if [ $? -eq 0 ]; then
echo 'Rabbit is started: http://localhost:15672/ username: guest password: guest'
else
echo 'Rabbit did not start';
exit 1;
fi
else
echo 'Rabbit is already running'
fi
Functions are great to clean up the logic in scripts making them easier to maintain and read. All variables are global in bash. To manipulate a variable only within the scope of the function, declare the variable in the function body using the 'local' keyword.
echo_function () {
echo 'Welcome to function one!'
}
echo_function
There are a few ways to return a value. In this first example the 'return' keyword is used, and '$?' to output what the function returned after its execution. This is generally used to check the exit status of a function, so only a numberic value can be returned.
return_example () {
return 'Hello!'
}
return_example
echo $?
Returning a string value can be done by setting an arguement.
return_string () {
variable_defined_in_function="I was generated in a function. Nice to meet you!"
}
return_string
echo $variable_defined_in_function
Here we will capture the output of an echo inside function into a variable defined outside of the function. Then echo this externally defined variable. The internal variable has the local keyword, so its not global.
stdout_return_value () {
local variable_defined_in_function="I was generated in a function. Nice to meet you!"
echo "$func_result"
}
stdout_return_value="$(stdout_return_value)"
echo $stdout_return_value
Finally a few examples of working with parameters and functions.
arg_function () {
echo "Args 1 and 2: $1 $2"
echo "Number of args: $#"
echo "Total Args: $*"
}
arg_function "A" "B" "C"
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