Execution hook examples

04/25/2022 Contributors

Use the following examples to get an idea of how to structure your execution hooks. You can use these hooks as templates, or as test scripts.

Simple success example

This is an example of a simple hook that succeeds and writes a message to standard output and standard error.

#!/bin/sh

# success_sample.sh
#
# A simple noop success hook script for testing purposes.
#
# args: None
#


#
# Writes the given message to standard output
#
# $* - The message to write
#
msg() {
    echo "$*"
}


#
# Writes the given information message to standard output
#
# $* - The message to write
#
info() {
    msg "INFO: $*"
}

#
# Writes the given error message to standard error
#
# $* - The message to write
#
error() {
    msg "ERROR: $*" 1>&2
}


#
# main
#

# log something to stdout
info "running success_sample.sh"

# exit with 0 to indicate success
info "exit 0"
exit 0

Simple success example (bash version)

This is an example of a simple hook that succeeds and writes a message to standard output and standard error, written for bash.

#!/bin/bash

# success_sample.bash
#
# A simple noop success hook script for testing purposes.
#
# args: None


#
# Writes the given message to standard output
#
# $* - The message to write
#
msg() {
    echo "$*"
}


#
# Writes the given information message to standard output
#
# $* - The message to write
#
info() {
    msg "INFO: $*"
}

#
# Writes the given error message to standard error
#
# $* - The message to write
#
error() {
    msg "ERROR: $*" 1>&2
}


#
# main
#

# log something to stdout
info "running success_sample.bash"

# exit with 0 to indicate success
info "exit 0"
exit 0

Simple success example (zsh version)

This is an example of a simple hook that succeeds and writes a message to standard output and standard error, written for Z shell.

#!/bin/zsh

# success_sample.zsh
#
# A simple noop success hook script for testing purposes.
#
# args: None
#


#
# Writes the given message to standard output
#
# $* - The message to write
#
msg() {
    echo "$*"
}


#
# Writes the given information message to standard output
#
# $* - The message to write
#
info() {
    msg "INFO: $*"
}

#
# Writes the given error message to standard error
#
# $* - The message to write
#
error() {
    msg "ERROR: $*" 1>&2
}

#
# main
#

# log something to stdout
info "running success_sample.zsh"

# exit with 0 to indicate success
info "exit 0"
exit 0

Success with arguments example

The following example demonstrates how you can use args in a hook.

#!/bin/sh

# success_sample_args.sh
#
# A simple success hook script with args for testing purposes.
#
# args: Up to two optional args that are echoed to stdout

#
# Writes the given message to standard output
#
# $* - The message to write
#
msg() {
    echo "$*"
}


#
# Writes the given information message to standard output
#
# $* - The message to write
#
info() {
    msg "INFO: $*"
}

#
# Writes the given error message to standard error
#
# $* - The message to write
#
error() {
    msg "ERROR: $*" 1>&2
}


#
# main
#

# log something to stdout
info "running success_sample_args.sh"


# collect args
arg1=$1
arg2=$2

# output args and arg count to stdout
info "number of args: $#"
info "arg1 ${arg1}"
info "arg2 ${arg2}"

# exit with 0 to indicate success
info "exit 0"
exit 0

Pre-snapshot / post-snapshot hook example

The following example demonstrates how the same script can be used for both a pre-snapshot and a post-snapshot hook.

#!/bin/sh

# success_sample_pre_post.sh
#
# A simple success hook script example with an arg for testing purposes
# to demonstrate how the same script can be used for both a prehook and posthook
#
# args: [pre|post]

# unique error codes for every error case
ebase=100
eusage=$((ebase+1))
ebadstage=$((ebase+2))
epre=$((ebase+3))
epost=$((ebase+4))


#
# Writes the given message to standard output
#
# $* - The message to write
#
msg() {
    echo "$*"
}


#
# Writes the given information message to standard output
#
# $* - The message to write
#
info() {
    msg "INFO: $*"
}

#
# Writes the given error message to standard error
#
# $* - The message to write
#
error() {
    msg "ERROR: $*" 1>&2
}


#
# Would run prehook steps here
#
prehook() {
    info "Running noop prehook"
    return 0
}

#
# Would run posthook steps here
#
posthook() {
    info "Running noop posthook"
    return 0
}


#
# main
#

# check arg
stage=$1
if [ -z "${stage}" ]; then
    echo "Usage: $0 <pre|post>"
    exit ${eusage}
fi

if [ "${stage}" != "pre" ] && [ "${stage}" != "post" ]; then
    echo "Invalid arg: ${stage}"
    exit ${ebadstage}
fi

# log something to stdout
info "running success_sample_pre_post.sh"

if [ "${stage}" = "pre" ]; then
    prehook
    rc=$?
    if [ ${rc} -ne 0 ]; then
        error "Error during prehook"
    fi
fi

if [ "${stage}" = "post" ]; then
    posthook
    rc=$?
    if [ ${rc} -ne 0 ]; then
        error "Error during posthook"
    fi
fi

exit ${rc}

Failure example

The following example demonstrates how you can handle failures in a hook.

#!/bin/sh

# failure_sample_arg_exit_code.sh
#
# A simple failure hook script for testing purposes.
#
# args: [the exit code to return]
#


#
# Writes the given message to standard output
#
# $* - The message to write
#
msg() {
    echo "$*"
}


#
# Writes the given information message to standard output
#
# $* - The message to write
#
info() {
    msg "INFO: $*"
}

#
# Writes the given error message to standard error
#
# $* - The message to write
#
error() {
    msg "ERROR: $*" 1>&2
}


#
# main
#

# log something to stdout
info "running failure_sample_arg_exit_code.sh"

argexitcode=$1

# log to stderr
error "script failed, returning exit code ${argexitcode}"

# exit with specified exit code
exit ${argexitcode}

Verbose failure example

The following example demonstrates how you can handle failures in a hook, with more verbose logging.

#!/bin/sh

# failure_sample_verbose.sh
#
# A simple failure hook script with args for testing purposes.
#
# args: [The number of lines to output to stdout]


#
# Writes the given message to standard output
#
# $* - The message to write
#
msg() {
    echo "$*"
}


#
# Writes the given information message to standard output
#
# $* - The message to write
#
info() {
    msg "INFO: $*"
}

#
# Writes the given error message to standard error
#
# $* - The message to write
#
error() {
    msg "ERROR: $*" 1>&2
}


#
# main
#

# log something to stdout
info "running failure_sample_verbose.sh"


# output arg value to stdout
linecount=$1
info "line count ${linecount}"

# write out a line to stdout based on line count arg
i=1
while [ "$i" -le ${linecount} ]; do
    info "This is line ${i} from failure_sample_verbose.sh"
    i=$(( i + 1 ))
done

error "exiting with error code 8"
exit 8

Failure with an exit code example

The following example demonstrates a hook failing with an exit code.

#!/bin/sh

# failure_sample_arg_exit_code.sh
#
# A simple failure hook script for testing purposes.
#
# args: [the exit code to return]
#


#
# Writes the given message to standard output
#
# $* - The message to write
#
msg() {
    echo "$*"
}


#
# Writes the given information message to standard output
#
# $* - The message to write
#
info() {
    msg "INFO: $*"
}

#
# Writes the given error message to standard error
#
# $* - The message to write
#
error() {
    msg "ERROR: $*" 1>&2
}


#
# main
#

# log something to stdout
info "running failure_sample_arg_exit_code.sh"

argexitcode=$1

# log to stderr
error "script failed, returning exit code ${argexitcode}"

# exit with specified exit code
exit ${argexitcode}

Success after failure example

The following example demonstrates a hook failing the first time it is run, but succeeding after the second run.

#!/bin/sh

# failure_then_success_sample.sh
#
# A hook script that fails on initial run but succeeds on second run for testing purposes.
#
# Helpful for testing retry logic for post hooks.
#
# args: None
#

#
# Writes the given message to standard output
#
# $* - The message to write
#
msg() {
    echo "$*"
}


#
# Writes the given information message to standard output
#
# $* - The message to write
#
info() {
    msg "INFO: $*"
}

#
# Writes the given error message to standard error
#
# $* - The message to write
#
error() {
    msg "ERROR: $*" 1>&2
}


#
# main
#

# log something to stdout
info "running failure_success sample.sh"


if [ -e /tmp/hook-test.junk ] ; then
    info "File does exist.  Removing /tmp/hook-test.junk"
    rm /tmp/hook-test.junk
    info "Second run so returning exit code 0"
    exit 0
else
    info "File does not exist.  Creating /tmp/hook-test.junk"
    echo "test" > /tmp/hook-test.junk
    error "Failed first run, returning exit code 5"
    exit 5
fi