Shell Script Template

Posted on | Edited on | In

This is a good script template which returns JSON response, it has exit hook, logs and arguments checking. I will continuously update it if I find good patterns.

Use Python script is more developer friendly and easy to maintain.

对于一般用途的script，有几点需要注意:

  1. shebang 必须有 #!/usr/bin/env bash or #!/usr/bin/env sh
  2. debug set 放开头， 如同这里一样
  3. usage 函数格式要清晰，可以参考这个例子，且必须有-h/--help flag
  4. 传入的argument 要检查个数，以及是否为空
  5. 参数输入多多测试不同情况
  6. 可能需要log，可用temp 以及 exit hook解决，log放 /tmp directory
  7. 输出信息用[date time] prefix, 可以用LogMsg function wrap一下

Using # for comment is preferred, but you can comment multi-line by heredoc:

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: <<'END_COMMENT'
...
END_COMMENT
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#!/usr/bin/env bash
#########################################################################
# Please insert the update at top of the logs
# Date           Author           Description
#
#########################################################################
## syntax check only, dry run
#set -n
## add line number for -x
export PS4='$LINENO + '
## pipeline subcommand failure check
set -o pipefail
## e: command line failure check
## u: undefined variable check
## x: print command executed
set -eux

## find canonical file path
## or you can restrict run script in it's current directory
CUR_PATH=$(dirname $(readlink -f $0))
source $CUR_PATH/<env file>
JQ="$CUR_PATH/jq"

## create log file for this script
OUT_FILE=$(mktemp /tmp/log.XXXX)
#OUT_FILE=/tmp/log

########################### function #########################
function exitHook {
  rm -f $OUT_FILE
  rm -f ${OUT_FILE}.out
  rm -f ${OUT_FILE}.err
}
## clean job for log file, you can add other signals
trap exitHook EXIT

function usage() {
 echo "<Description>"
 echo
 echo "Usage:"
 echo "  $0 [...]"
 echo
 echo "Flags:"
 echo "  -h, --help     help info"
}

## this is for return json format messages
function returnError() {
  msg="$1"
  echo "{\"result\": \"Failure\", \"message\": \"$msg\"}" |${JQ} '.'
  exit 1
}

function returnInfo() {
  msg="$1"
  echo "{\"result\": \"Success\", \"message\": \"$msg\"}" |${JQ} '.'
  exit 0
}

########################## main ##############################
## declare input parameters
P1=""
P2=""

## check script parameters
if [[ $# -eq 0 ]]; then
  msg="No command-line arguments were specified..."
  returnError "$msg"
fi

while [[ $# -gt 0 ]]
do
  case "$1" in
    -p1|--p11)
       shift
       P1=$1
       shift;;

    -p2|--p22)
       shift
       P2=$1
       shift;;

    *) msg="$0: Bad Usage..."
       returnError "$msg"
  esac
done

## double check or restrict parameters
if [[ "X${P1}" = "X" ]]; then
  msg="-p1 was not specified"
  returnError "$msg"
elif [[ "X${P2}" = "X" ]]; then
  msg="-p2 was not specified"
  returnError "$msg"
fi

## then do the job, when you run some commands in script 
## you can redirect the normal output to ${OUT_FILE}.out
## and error output to ${OUT_FILE}.err by:
command 1>>${OUT_FILE}.out 2>>${OUT_FILE}.err

if [[ $? = 0 ]]; then
    msg="Run command successfully..."
    returnInfo "$msg"
else
    ## parse err log file and return message
    msg=$(cat ${OUT_FILE}.err|sed -e 's/"/\\"/g')
    returnError "$msg"
fi
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