Use a defined webhook to post a message from the command-line as a parameter, standard input, or a file into Slack/Mattermost. Take advantage of colors, icons, and markdown to enhance your message.
Shell script
The following shell script provides an easy way to post a message carried as a parameter, standard input, or a file.
#!/bin/bash
# send message to slack channel
# define the boundaries after which the message will be sent will be sent as an attachment
# count "c" characters or "l" lines from stdin
stdin_check="l"
# define number of characters or lines from stdin
stdin_count="2"
# define usage function
function usage {
echo "Basic connection parameters:"
echo " -h hook_url"
echo " -c channel"
echo " -u username"
echo " -i icon"
echo " -p enable|disable (markdown)"
echo
echo "Define message using file contents:"
echo " -F \"file\""
echo " -C color"
echo " -T \"title\""
echo
echo "Define message using parameter:"
echo " -m \"message\""
echo
echo "Otherwise, define message using standard input."
echo
}
# curl is an essential application used to send message
if ! command -v curl &>/dev/null; then
echo "Error: curl is missing"
exit 1
fi
# display usage if no arguments are passed
if [ "$#" = "0" ];then
usage;
exit;
fi
# parse arguments
while getopts "h:c:u:m:i:C:F:T:p:" option; do
case $option in
"h")
slack_hook_url=${OPTARG}
;;
"c")
slack_channel=${OPTARG}
;;
"u")
slack_username=${OPTARG}
;;
"i")
slack_icon=${OPTARG}
;;
"C")
slack_color=${OPTARG}
;;
"F")
slack_file=${OPTARG}
;;
"T")
slack_title=$(echo -e "${OPTARG}" | sed 's/\"/\\"/g' | sed "s/'/\'/g" | sed 's/`/\`/g')
;;
"p")
if [ "${OPTARG}" == "disable" ]; then
slack_markdown="false"
else
slack_markdown="true"
fi
;;
"m")
slack_message=${OPTARG}
;;
\?|:)
usage
exit
;;
esac
done
# verify basic parameters
if [ -z "$slack_hook_url" ] || [ -z "$slack_channel" ] || [ -z "$slack_username" ]; then
echo "Error: Basic connection parameters are missing"
exit 1
fi
# set default icon if not defined
if [ -z "$slack_icon" ]; then
slack_icon="ghost"
fi
# read message
if [ -n "$slack_file" ]; then
if [ -f "$slack_file" ]; then
# read message using file (-F)
file=$(cat $slack_file)
else
echo "Error: File not found"
exit 1
fi
fi
if [ -n "$slack_message" ]; then
# read message (-m) message parameter
message="$slack_message"
else
if [ ! -t 0 ]; then
# read message from stdin
message=$(cat /dev/stdin)
fi
fi
# define header and color
if [ -n "$slack_title" ]; then
title="\"title\":\"${slack_title}\" ,"
if [ -z "$slack_file" ]; then
file="$message"
slack_file="/dev/null"
fi
else
title=""
fi
if [ -n "$slack_color" ]; then
color="\"color\":\"${slack_color}\" ,"
if [ -z "$slack_file" ]; then
file="$message"
slack_file="/dev/null"
fi
else
color=""
fi
# do not send empty message
if [ -z "${message}" ] && [ -z "${file}" ]; then
echo "Error: There is nothing to send"
exit 1
fi
# send message as attachment if it is bigger then defined values so it can be folded up
if [ -z "$slack_file" ]; then
count=$(echo -e "${message}" | wc -${stdin_check})
if [ "$count" -gt "$stdin_count" ]; then
# activate small cheat
file="$message"
slack_file="/dev/null"
fi
fi
# escape message and prepare text property
if [ -n "${message}" ]; then
escaped_message=$(echo -e "${message}" | sed 's/\"/\\"/g' | sed "s/'/\'/g" | sed 's/`/\`/g')
text="\"text\": \"${escaped_message}\""
fi
# escape file contents and prepare text property
if [ -n "${file}" ]; then
escaped_file=$(echo -e "${file}" | sed 's/\"/\\"/g' | sed "s/'/\'/g" | sed 's/`/\`/g')
file="\"text\": \"${escaped_file}\""
fi
# define json
markdown="\"mrkdwn\": false,"
if [ -n "$slack_file" ]; then
if [ "$slack_markdown" == "true" ]; then
markdown="\"mrkdwn_in\": [\"text\"],"
fi
json="{\"channel\": \"${slack_channel}\", \"username\":\"${slack_username}\", \"icon_emoji\":\":${slack_icon}:\", \"attachments\":[{ ${color} ${title} ${markdown} ${file}}]}"
else
if [ "$slack_markdown" == "true" ]; then
markdown="\"mrkdwn\": true,"
fi
json="{\"channel\": \"${slack_channel}\", \"username\":\"${slack_username}\", \"icon_emoji\":\":${slack_icon}:\", ${markdown} ${text}}"
fi
# send message
curl -s -d "payload=$json" $slack_hook_urlSample usage
Display usage information
$ bash slack_message.sh
Basic connection parameters: -h hook_url -c channel -u username -i icon -p enable|disable (markdown) Define message using file contents: -F "file" -C color -T "title" Define message using parameter: -m "message" Otherwise, define message using standard input.
Post simple message
$ bash slack_message.sh -h https://hooks.slack.com/services/D21FA21F/F9PATXG7R/38BepMtJ5NxF8yV2fQsHjen1 -c system-operations -u sysopsusr -i penguin -m "$(hostname) timezone is $(cat /etc/timezone)"
Post a multi-line message
$ bash slack_message.sh -h https://hooks.slack.com/services/D21FA21F/F9PATXG7R/38BepMtJ5NxF8yV2fQsHjen1 -c system-operations -u sysopsusr -i terminal -C 1974D2 -m "$(hostname) timezone is $(cat /etc/timezone)\nDatetime is $(date)"
Post file as a message
$ bash slack_message.sh -h https://hooks.slack.com/services/D21FA21F/F9PATXG7R/38BepMtJ5NxF8yV2fQsHjen1 -c system-operations -u sysopsusr -i terminal -F /proc/mdstat -T "$(hostname) software raid status"
Post message from standard input
$ df -h | sed -e '1s/^/```/' -e '$a```' | bash slack_message.sh -h https://hooks.slack.com/services/D21FA21F/F9PATXG7R/38BepMtJ5NxF8yV2fQsHjen1 -c system-operations -u sysopsusr -i comet -C 1974D2 -p enable -T "$(hostname) system disk space usage"
Additional information
Use color to indicate success or failure.
Enable markdown to enhance your message using its simple syntax.
Define the boundaries (number of lines or a number of characters) after which the message will be sent as an attachment.
Remember about optional title header as it can help you to shortly describe long messages, especially those including files.