make tail wait for a file to exist

Question

tail -f bar/somefile.log would fail immediately when somefile.log does not exist. How do I make tail indefinitely wait for that file to be created (which will happen in a few moments)?

Update: using -F, I see:

tail: cannot open `bar/somefile.log' for reading: No such file or directory
tail: cannot watch parent directory of `bar/somefile.log': No such file or directory

because bar does't exist yet (it will be created in a few moments). when bar was created, and somefile.log was touched, tail didn't pick up the changes at all.

score 43 · Answer 1 · answered Feb 20 '12 at 19:18

43

You're not mentioning which OS you need it for, but tailon linux has the --retry and --follow options that will do just that;

tail --retry --follow=name somefile.log

answered Feb 20 '12 at 19:18

Joachim Isaksson

803
5
7

8

thanks, or `tail -F somefile.log`. but then, tail fails for a different reason (i've updated my question) – Sridhar Ratnakumar Feb 20 '12 at 19:35

cYrus · Accepted Answer · 2012-02-21T16:23:45.627

31

This works:

while ! tail -f bar/somefile.log ; do sleep 1 ; done

edited Feb 21 '12 at 16:23

answered Feb 20 '12 at 19:15

cYrus

21,379
8
74
79

this is what finally worked for me (for missing parent directory cases). – Sridhar Ratnakumar Feb 20 '12 at 19:48
Will this work for Mac? – mCeviker Aug 10 '18 at 20:45

score 10 · Answer 3 · answered Feb 20 '12 at 23:48

10

Create the file first:

touch somefile ; tail -f somefile

answered Feb 20 '12 at 23:48

psusi

7,837
21
25

Nice elegant logical solution. – CarComp Jun 12 '19 at 19:37
Depending on the application, this might be the best solution. Thanks! – Alex Kaszynski Jan 17 '21 at 17:21

make tail wait for a file to exist

3 Answers3