The purpose of this document is to explain how to cope with the percentage sign (%) in a crontab entry.
Usually, a % is used to denote a new line in a crontab entry. The first % is special in that it denotes the start of STDIN for the crontab entry's command. A trivial example is:
* * * * * cat - % another minute has passed
This would output the text
another minute has passed
After the first %, all other %s in a crontab entry indicate a new line. So a slightly different trivial example is:
* * * * * cat - % another % minute % has % passed
This would output the text
another minute has passed
Note how the % has been used to indicate a new line.
The problem is how to use a % in a crontab line to as a % and not as a new line. Many manuals will say escape it with a . This certainly stops its interpretation as a new line but the shell running the cron job can leave the in. For example:
* * * * * echo '\% another \% minute \% has \% passed'
would output the text
\% another \% minute \% has \% passed
Clearly, not what was intended.
A solution is to pass the text through sed. The crontab example now becomes:
* * * * * echo '\% another \% minute \% has \% passed'| sed -e 's|\||g'
This would output the text
% another % minute % has % passed
which is what was intended.
This technique is very useful when using a MySQL command within a crontab. MySQL command can often have a % in them. Some example are:
- SET @monyy=DATE_FORMAT(NOW(),"%M %Y")
- SELECT * FROM table WHERE name LIKE 'fred%'
So, to have a crontab entry to run the MySQL command
mysql -vv -e "SELECT * FROM table WHERE name LIKE Fred%'" member_list
would have to appear in the crontab as
echo "SELECT * FROM table WHERE name LIKE 'Fred\%'" | sed -e 's|\||g' | mysql -vv member_list