How to create shell script for a cron job with hidden debug information

Create a shell script for a cron job with hidden debug information shown only when executed inside the terminal.

The idea behind this is quite simple as we need to verify if stdin (file descriptor __), stdout (file descriptor 1), or stderr (file descriptor 2) is associated with the terminal. If not, then the shell script is executed as a cron job, so any debug message can be omitted.

#!/bin/bash
# cron job template with debug information

# display debug information 
# only if $terminal variable is set to 1
emit() {
  if [ "$terminal" -eq "1" ]; then
    printf "%s\n" "$*" 
  fi
}

# determine if standard input (file descriptor) is opened on a terminal
# and set $terminal variable accordingly
if [ -t 0 ] ; then
  terminal=1
else
  terminal=0
fi  

emit "Script name is $(basename $0)" 
emit "Script location is $(readlink -f $0)" 
emit "Script is executed on $TERM"
emit "Script is executed from $PWD directory"
emit "Script is executed with $USER permissions"
if [ -n "$SUDO_USER" ]; then
  emit "Script is executed using sudo by $SUDO_USER ($SUDO_UID:$SUDO_GID)"
fi
emit 
emit "Script is using path defined as $PATH"
emit "Script LANG variable is $(locale | awk -F '=' '/LANG=/ {print $2}')"
emit
emit "Execution start: $(date)"

# perform real operations here

emit "Execution end: $(date)"

Sample output inside the terminal.

~# bash bin/cron_job_template.sh

Script name is cron_job_template.sh
Script location is /root/bin/cron_job_template.sh
Script is executed on screen
Script is executed from /root directory
Script is executed with root permissions

Script is using path defined as /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
Script LANG variable is C.UTF-8

Execution start: Tue Dec 26 13:25:50 UTC 2017
Execution end: Tue Dec 26 13:25:50 UTC 2017