bash 将条目插入 crontab 除非它已经存在（如果可能，作为单行）
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Insert entry into crontab unless it already exists (as one-liner if possible)
提问by fredrik
What's the preferred method to insert an entry into /etc/crontab unless it exists, preferably using a one-liner?
将条目插入 /etc/crontab 的首选方法是什么，除非它存在，最好使用单行？
Here's my example entry I wish to place into /etc/crontab unless it already exists in there.
这是我希望放入 /etc/crontab 的示例条目，除非它已经存在于那里。
*/1 * * * * some_user python /mount/share/script.py
I'm on CentOS 6.6 and so far I have this:
我在 CentOS 6.6 上，到目前为止我有这个：
if grep "*/1 * * * * some_user python /mount/share/script.py" /etc/crontab; then echo "Entry already in crontab"; else echo "*/1 * * * * some_user python /mount/share/script.py" >> /etc/crontab; fi
回答by arco444
You can do this:
你可以这样做：
grep 'some_user python /mount/share/script.py' /etc/crontab || echo '*/1 * * * * some_user python /mount/share/script.py' >> /etc/crontab
If the line is absent, grepwill return 1, so the right hand side of the or ||will be executed.
如果该行不存在，grep将返回1，因此||将执行or 的右侧。
回答by dleon
You can do it like this:
你可以这样做：
if grep "\*\/5 \* \* \* \* /usr/local/bin/test.sh" /var/spool/cron/root; then echo "Entry already in crontab"; else echo "*/5 * * * * /usr/local/bin/test.sh" >> /var/spool/cron/root; fi
Or even more terse:
或者更简洁：
grep '\*\/12 \* \* \* \* /bin/yum makecache fast' /var/spool/cron/root \
|| echo '*/12 * * * * /bin/yum makecache fast' >> /var/spool/cron/root
回答by karpada
Factoring out the filename & using the q & F options
file="/etc/crontab"; grep -qF "some_user python /mount/share/script.py" "$file" || echo "*/1 * * * * some_user python /mount/share/script.py"
分解出文件名并使用 q & F 选项
file="/etc/crontab"; grep -qF "some_user python /mount/share/script.py" "$file" || echo "*/1 * * * * some_user python /mount/share/script.py"
