I’m trying to create an alias to open up my log fie

alias open_log='date=`date +%y%m%d`;sudo tail -n 10 ~/logs/reconfig-$date.log;'

When I run that alias


I got

tail: cannot open ‘/home/benu/logs/reconfig-.log’ for reading: No such file or directory

But if I run

"what I set for that alias"

date=`date +%y%m%d`;sudo tail -n 10 ~/logs/reconfig-$date.log;

It works perfectly fine.

+ service iptables save
iptables: Saving firewall rules to /etc/sysconfig/iptables: [  OK  ]
+ mkdir -p /etc/nginx/sites-available
+ cp /root/portal-data/sites-available/default-https /etc/nginx/sites-available/default
+ '[' '!' -f /etc/ssl/mywifibusiness.trg.telenet.be.cert.pem ']'
+ echo 'Error: Unable to find certificate at /etc/ssl/mywifibusiness.trg.telenet.be.cert.pem'
Error: Unable to find certificate at /etc/ssl/mywifibusiness.trg.telenet.be.cert.pem
+ exit 1
Error: Executing /home/benu/reconfig.d/70-ssc-portal.sh returned 1
Reconfigure aborted

Why they’re behaving different ? Can anyone elaborate ?

How do I fix my alias to make it work ?

  • 1
    alias open_log="sudo tail -n 10 ~/logs/reconfig-$(date +%y%m%d).log" May 4, 2017 at 14:50
  • 1
    The only system I have access to is an Ubuntu system, and this seems to work there. @Christopher I don't think OP wants weak quotes here
    – Fox
    May 4, 2017 at 14:55
  • I even tried date=date +%y%m%d; echo -e "~/logs/reconfig-$date.log" | sudo tail -n 10; , but it does is printing out my path command, rather than running that command. How do I fix it guys ?
    – code-8
    May 4, 2017 at 14:56
  • Works for me, though setting a variable in an alias a bit weird (it stays set in the outside context). Do you have an alias or function overriding date or something like that?
    – ilkkachu
    May 4, 2017 at 15:01
  • 1
    Why would you want to open a file in your home directory as root? Why not just alias open_log="tail -n 10 ~/logs/reconfig-$(date +%y%m%d).log;"?
    – terdon
    May 4, 2017 at 15:02

1 Answer 1


Sorry, @ihue. I got this wrong to start. Kudos to @ilkkachu.

Compare the alias with the command line, posted before the edit:

alias 'date=date +%y%m%d;sudo tail -n 10 ~/logs/reconfig-$date.log;'
date=`date +%y%m%d`;sudo tail -n 10 ~/logs/reconfig-$date.log;

The alias is missing the backticks. Also, the backticks are all but antiquated. Use the following form for command substitution: $(command).

Double quotes work as follows, which sets the date each time the alias was set.

alias open_log="sudo tail -n 10 ~/logs/reconfig-$(date +%y%m%d).log"

Single quotes work dynamically, setting the date each time you call the alias.

alias open_log='sudo tail -n 10 ~/logs/reconfig-$(date +%y%m%d).log'
  • 2
    That alias, with the double-quotes, would expand the command substitution at the time the alias is set, not when it's executed.
    – ilkkachu
    May 4, 2017 at 15:01
  • Please note the accurate comment by @ilkkachu. In other words, every time you source your aliases, however that may be - at log in time or manually, perhaps - the date is set at that time, not dynamically every time you call the alias. May 4, 2017 at 15:04
  • 2
    ...of course with single-quotes it would be the opposite, compare alias d1='echo $(date +%T)' d2="echo $(date +%T)"
    – ilkkachu
    May 4, 2017 at 15:19
  • Thank you @ilkkachu. I had the wrong understanding to start. May 4, 2017 at 15:55

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