How do I Regex match file names in bash? i.e. tail -f /var/log/(syslog|mail.log)

Question

I've been typing commands like the (the long way) for my whole life.

tail -f /var/log/syslog /var/log/mail.log /var/log/mail.err

This is probably a really basic question, but I had a hard time finding the answer.

Is there a regex way to match multiple files in the folder without retyping the location each time?

This saves me a few keystrokes, but not many

export LOGDIR=/var/log
tail -f $LOGDIR/syslog $LOGDIR/mail.log $LOGDIR/mail.err 

And sometimes I want multiple locations... I want to figure out something like this:

tail -f /var/log/(mail*|syslog|nginx/*)

(but actually have it work)

Answer 1

Use brace-expansion.

tail -f /var/log/{mail*,syslog,nginx/*}

Example:

$ tree
├── mail.err
├── mail.log
├── nginx
│   ├── a
│   ├── b
│   └── c
├── notthis
└── syslog
$ echo {mail*,syslog,nginx/*}
mail.err mail.log syslog nginx/a nginx/b nginx/c

Answer 2

In bash:

shopt -s extglob ## enable extend-glob if not enabled; default is "on"
tail -f /var/log/+(syslog|mail.+(log|err))

or apparently:

tail -f /var/log/+(syslog|mail*)

Please note that these are filename globing and applicable only for the files, so you should not expect to have expansion on the path like in nginx/* you said; instead you can prefer to use brace-expansion based solution and answer given by Quasímodo or just explicitly separate that as another parameter to the command:

tail -f /var/log/+(syslog|mail*) /var/log/nginx/*

Answer 3

Doing tail -f file1 file2 will follow file1 until "done" (never) before it gets to file2. However, multitail handles multiple files simultaneously. sudo apt install multitail;man multitail.