Run a cron job manually and immediately

crontab -l

# Edit this file to introduce tasks to be run by cron.
#
# Each task to run has to be defined through a single line
# indicating with different fields when the task will be run
# and what command to run for the task
#
# To define the time you can provide concrete values for
# minute (m), hour (h), day of month (dom), month (mon),
# and day of week (dow) or use '*' in these fields (for 'any').#
# Notice that tasks will be started based on the cron's system
# daemon's notion of time and timezones.
#
# Output of the crontab jobs (including errors) is sent through
# email to the user the crontab file belongs to (unless redirected).
#
# For example, you can run a backup of all your user accounts
# at 5 a.m every week with:
# 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/
#
# For more information see the manual pages of crontab(5) and cron(8)
#
# m h  dom mon dow   command

X=Y
1 2 3 4 5 6 echo "Hello, world"
1 2 3 4 5 6 echo "Goodby, cruel world"
1 2 3 4 5 6 echo "Please spare me the drama"

cronTest

#!/bin/bash

# Execute a user crontab entry with the proper environment

DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"

env -i bash --noprofile --norc -c "$DIR/cronTest2 $USER"

cronTest2

#!/bin/bash

# Prompt user for a user crontab entry to execute

function deleteTempFile {
  rm -f $TEMP_FILE
}

function debug {
  if [ "$DEBUG" ]; then >&2 printf "$1\n"; fi
}

function isValidLineNumber {
  # $1 - number of lines
  # $2 - requested line number
  if [[ -n "${2//[0-9]+/}" ]] && (( $2 <= $1 )); then echo true; else echo false; fi
}

function isVariableAssignment {
  [[ "$( echo "$1" | grep "=" )" ]]
}

function makeTempCrontab {
  local -r ASTERISK=\\*
  local -r NUMBER='[[:digit:]]{1,2}'
  local -r NUMBERS="$NUMBER(,$NUMBER)+"
  local -r CRON="^(($ASTERISK|$NUMBER|$NUMBERS)[[:space:]]+)"
  local -r CRON5_REGEX="$CRON{5}"
  local -r CRON6_REGEX="$CRON{6}"

  rm -f "$TEMP_FILE"

  local -r ALL_LINES="$( crontab -l )"

  # Ignore empty lines and lines starting with # (comment lines)
  local -r LINES="$( 
    echo "$ALL_LINES" | \
    grep -v '^[[:space:]]*#' | \
    grep -v '^[[:space:]]*$'
  )"
  
  if [[ -z "$LINES" ]]; then
    echo "Your crontab is empty, nothing to do"
    exit 1
  fi

  IFS=$'\n' 
  for LINE in $LINES; do
    LINE="$( echo "$LINE" | sed 's/\s\+$//e' )" # remove trailing space
    if [ "$( echo "$LINE" | grep "^$" )" ]; then  
      debug ""  # ignore empty line
    elif [ "$( echo "$LINE" | egrep "$CRON6_REGEX" )" ]; then
      debug "6 field date/time specifier: $LINE"
      # strip out when to run debug, leaving just the command to execute
      echo "$LINE" | cut -f 7- -d ' ' >> "$TEMP_FILE"
    elif [ "$( echo "$LINE" | egrep "$CRON5_REGEX" )" ]; then
      debug "5 field date/time specifier: $LINE"
      # strip out when to run debug, leaving just the command to execute
      echo "$LINE" | cut -f 6- -d ' ' >> "$TEMP_FILE"
    elif [ "$( echo "$LINE" | grep '^@' )" ]; then
      debug "@declaration: $LINE"
      # strip out @declaration, leaving just the command to execute
      echo "$LINE" | cut -f 2- -d ' ' >> "$TEMP_FILE"
    elif [ "$( echo "$LINE" | grep '=' )" ]; then
      debug "Variable assignment: $LINE"
      echo "$LINE"  >> "$TEMP_FILE"
    else
      debug "Ignored: $LINE"
    fi
  done
  unset IFS
}

function runUpToLine {
  # Scans up to given line number in $TEMP_FILE
  # Evaluates variable assignment
  # Executes specified line
  # Ignores remainder of file
  # Function definitions are not supported
  #
  # $1 - line number to run

  readarray CONTENTS < "$TEMP_FILE"
  for (( i=0; i<=$1; i++ )); do
    # >&2 echo "\$i=$i, \$1=$1, isVariableAssignment: $( isVariableAssignment $CONTENTS[$i] ), CONTENTS[$i]=${CONTENTS[$i]}"
    if isVariableAssignment ${CONTENTS[$i]} || (( $i == $1 )); then
      printf "\nEvaluating $(( i+1 )): ${CONTENTS[$i]}"
      eval "${CONTENTS[$i]}"
    fi
  done
}

function selectLine {
  >&2 echo "This is the crontab for $USER without comment lines or blank lines:"
  cat -n "$TEMP_FILE" >&2
  >&2 echo "Which line would you like to run as $USER now?"

  local -r NUM_LINES=$( cat "$TEMP_FILE" | wc -l )
  read LINE_NUMBER
  # >&2 echo "NUM_LINES=$NUM_LINES, LINE_NUMBER=$LINE_NUMBER;  valid: $( isValidLineNumber $NUM_LINES $LINE_NUMBER )"
  while [[ $( isValidLineNumber $NUM_LINES $LINE_NUMBER ) == false ]]; do
    >&2 echo "$LINE_NUMBER is not valid, please enter an integer from 1 to $NUM_LINES"
    read LINE_NUMBER
    # >&2 echo "NUM_LINES=$NUM_LINES, LINE_NUMBER=$LINE_NUMBER;  valid: $( isValidLineNumber $NUM_LINES $LINE_NUMBER )"
  done
  (( LINE_NUMBER-- ))
  echo ${LINE_NUMBER}
}

function doIt {
  export USER=$1
  local -r TEMP_FILE="$( mktemp crontabTest.XXX )"
  trap deleteTempFile EXIT

  makeTempCrontab
  local -r LINE_NUMBER="$( selectLine )"
  runUpToLine $LINE_NUMBER
}

doIt "$1" 

sampleOutput

$ cronTest
This is the crontab for  without comment lines or blank lines:
     1  X=Y
     2  echo "Hello, world"
     3  echo "Goodby, cruel world"
     4  echo "Please spare me the drama"
Which line would you like to run as  now?
55
55 is not valid, please enter an integer from 1 to 4
2

Evaluating 1: X=Y

Evaluating 2: echo "Hello, world"
Hello, world