Problem
You would like to copy the contents of a source directory to a destination directory without overwriting existing files on the destination.
Solution
You can use
rsync -a -v --ignore-existing source_dir/ dest_dir/
and you can also use the –dry-run option to test before running it.
Problem
You have defined a variable in a bash script (ie MY_FOLDER) but you also want to dynamically get the parent folder (ie MY_FOLDER can have multiple values).
Solution
Use the dirname as in the following
MY_FOLDER=/home/user/first_folder/second_folder MY_PARENT_FOLDER=$(dirname $MY_FOLDER) echo $MY_FOLDER echo $MY_PARENT_FOLDER ....... /home/user/first_folder/second_folder /home/user/first_folder
Problem
You would like to remove some lines from the bash history (ie using cut and paste with wrong values).
Solution
You can use the following, taken from the answer here
for i in {1..no_of_lines}; do history -d start_line; done
where start_line is the start of the lines you want to remove and no_of_lines is the number of lines you want to be removed.
Problem
You would like to send the error output from a command or a script to both an error file and an email.
Solution
By using tee, you could do the following:
command_with_parameters 2>&1 | tee /log_file_name | mail -s 'Command error' me@mydomain.com
Problem
You have a bash script that accepts parameter(s) but you want to give a default value for a missing parameter.
Solution
For example you have a script that accepts a parameter with the year and month (ie 201703), but you want to give it a default of two months ago if the parameter is missing.
#!/bin/bash
LM=$(date -d '2 month ago' +%Y%m)
YEARMONTH=${1:-${LM}}
echo $YEARMONTH