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  • BASH - Bourne again shell

  • To check the shell we're in

    echo $SHELL

  • To list all files under a directory (even hidden ones)

    ls -al

    "a" stands for all and "i" stands for long list In the output columns 1) dash denotes files 2) d denotes directory 3) the r, w and x denote read write and execute perms 4) rhyme are users and groups 5) the next column is the size in bytes 6) file name is in the last column

  • To rename a file

    mv #oldFileName #newFileName

  • rm to delete a file

  • To copy content from one file to another file

cat #oneFile > #anotherFile "less" #filename to scroll through file contents

  • nano is a text editopr used in the shell itself

    nano #filename CTRL + S to save file CTRL + X to exit

  • "mkdir" to make a new directory

  • "touch" to add new files into the directory

  • "rmdir" to delete only EMPTY directories

  • "rm -ir #dirname

    • "i" confirms if you want to delete everything in the directory
    • "r" recursively deletes everything in the directory and the then the directory itself

find / -name "backup" 2>/dev/null

- This command here is finding a file with name backup in it starting the search from the directory itself and 2> is pushing all the errors if any to /dev/null

history

- this command gives you the history of all the commands we used

Aliases

  • To keep aliases in a file

    nano .bash aliases alias fbackup= 'find ~ -name "backup*" 2>/dev/null' - so here we're creationg an alias named fbackups and to that we're assigning the above command - Now to get the bash shell to look at the file immediately > source .bash_aliases

    backup - will give you the files with name backup in it

Writing a Shell Script

nano myBackup #!/bin/bash - this is a note to the interpreter that this is a bash file

  • Anything starting with a # is a comment

myBackup: backup utility for dev directory

  • creating variable first

    BACKUP_PATH= "/home/rhyme/dev/" HOME_PATH= "/home/rhyme/" DATE= date +%d%m%Y - backtics tell the shell to execute whats inside - DATE here is a variable that holds the output from calling the date command BACKUP "backup_" EXT+".tar" - this tell the script to look for files with the name backup and extension tar FILE_NAME=$HOME_PATH $BACKUP $DATE $EXT - here we are referencing the variable using "$" sign echo $FILE_NAME ./myBackup

    tar cfz $FILE_NAME $BACKUP_PATH - this archives the dev directory and saves it as this filename - tar stands for tape archive - this tells tar to create a file with our filename and use the backup path ie our dev directory here - "z" here zips the script for us

  • To summarise

    #!/bin/bash #myBackup: backup utility for dev directory BACKUP_PATH= "/home/rhyme/dev/" HOME_PATH= "/home/rhyme/"] DATE= date +%d% m%Y BACKUP "backup_" EXT+".tar" FILE_NAME=$HOME_PATH $BACKUP $DATE $EXT #echo $FILE_NAME tar cf $FILE_NAME $BACKUP_PATH

  • now we have a bash script that will create a daily backup file

  • Permisions

    chmod u=rwx myBackup - what this does is it gives the user read write and execute perms on the myBackup script chmod go=rx myBackup - gives groups and others only read and execute perms of myBackup script ll myBackup - to view the perms chmod o-r myBackup - to remove read perms from others - "+r" to add those perms back

Bash Scripting and Creating a Cron Job with Crontab

if test -f "$FILE_NAME"; then > mail -A $FILE_NAME -s "TODAY's BAckup" johndoe@gmail.com

   - this will mail my backup in case the backup fails

else > echo $DATE " There was a problem creating ther backup file" >> $HOME_PATH/error.log fi

  • if the file doesn't exist then it will send out the message and putting it in an error log file by creating it

  • crontab A.K.A cron table is a job scheduler on Unix-like operating systems.

  • one uses cron to schedule jobs, also known as cron jobs, to run periodically at fixed times, dates, or intervals.

  • To create a new crontab

    crontab -e

    • m is for minute (1-60)
    • h is for hour (1-12)
    • dom is day of the month (1-31)
    • mon for month (1-12)
    • dow is day of the week (1-7)

0 2 * * * /home/rhyme/myBackup - This command makes our crontab for making daily backups at 2am everyday - * stands for all

  • to run a script every minute

            • /path/to/script

  • to delete all crontabs on my user account

    crontab -r

  • shortcuts to run crontab

    @yearly /path/to/job @annually /path/to/job - These are the same. It will run once a year. @monthly /path/to/job - runs once per month. @weekly /path/to/job -Run once a week. @daily /path/to/job @midnight /path/to/job - And these are the same-- you'll run once a day. - Daily is specific--it would schedule to run at midnight. This would be the same as '0 0 * * *'.

    @hourly /path/to/job - runs once every hour. @reboot /path/to/job - runs every time the system boots up