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* Description: Comment out and enable certain task on crontab by Linux shell script
* Date: 11:49 PM EST, 03/12/2018
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<1> In some case, for app server, when Linux system up, some certain crontab jobs need to be commented out first. After app up, then uncomment the jobs:
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     |__ o. Above action can be archived by manual work, but following shell script can manipulate crontab automatically.
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     |__ o. "Crontab -l" output is a text file, which can be written by ">"
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     |            # Keep the jobs, which need to be active as it is via "grep -v option".					 
     |            crontab -l | grep -v /u01/job_name_not_comment.sh > /u01/crontab_disable.txt
     |            
     |            # Comment out the jobs need to be disabled.		 
     |            crontab -l | grep /u01/job_name_comment.sh | sed '/\/u01\/job_name.sh/s!^!#Disabled#!' >> /u01/crontab_disable.txt
     |            
     |            # Writing the final result back to crontab as text file
     |            crontab < /u01/crontab_disable.txt
     |		 
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     |__ o. Now, "crontab -l" will show job got commented out with heads "#Disabled#":	 
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     |            #Disabled#/u01/job_name_comment.sh
     |            
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     |	 
     |__ o. Following command will remove "#Disabled#" to re-activate job on Crontab:			 
    
                  crontab -l | sed '/\/u01\/job_name.sh/s!#Disabled#!!' > /u01/crontab_enable.txt
                  crontab < /u01/crontab_enable.txt