Htydjtk

I want to find the age of the oldest file in a certain directory or return 0 if there aren't any files in this directory. I also need a one-line command doing it. So far this is my command for finding the age in seconds of the oldest file in the directory:

expr $(($(date +%s) - $(stat -c %Y $(ls -lt /path/to/dir/ | tail -1 | awk '{print $NF}'))))

The problem is that if there are no files it is returning the following error:

$ expr $(($(date +%s) - $(stat -c %Y $(ls -lt /path/to/dir/ | tail -1 | awk '{print $NF}'))))

stat: cannot stat ‘0’: No such file or directory

-bash: 1554373460 - : syntax error: operand expected (error token is "- ")

So in this case I want the command to return just 0 and to suppress the error printout.

If it must be one line:

stat -c %Y ./* 2>/dev/null | awk -v d="$(date +%s)" 'BEGIN {m=d} $0 < m {m = $0} END {print d - m}'

• 
  stat -c %Y ./* 2>/dev/null print the timestamp of all files, ignoring errors (so no files results in no output)


• 
  

  With awk:

  
  
  
  
  
  • 
    -v d="$(date +%s)" save the current timestamp in a variable d
    
  
  
  • 
    BEGIN {m=d} initialize m to d
    
  
  
  • 
    $0 < m {m = $0} keeping track of the minimum in m
    
  
  
  • 
    END {print d - m} print the difference.
  
  
  
  

With zsh and perl:

perl -le 'print 0+-M $ARGV[0]' /path/to/dir/*(N-Om[1])

(add the D glob qualifier if you also want to consider hidden files (but not . nor ..)).

Note that for symlinks, that considers the modification time of the file it resolves to. Remove the - in the glob qualifiers to consider the modification time of the symlink instead (and use (lstat$ARGV[0] && -M _) in perl to get the age of the symlink).

That gives the age in days. Multiply by 86400 to get a number of seconds:

perl -le 'print 86400*-M $ARGV[0]' /path/to/dir/*(N-Om[1])

• 
  (N-Om[1]): glob qualifier:
  
  
  
  
  • 
    N: turns on nullglob for that glob. So if there's no file in the directory, expands to nothing causing perl's -M to return undef.
  
  
  • 
    -: causes next glob qualifiers to apply on the target of symlinks
  
  
  • 
    Om: reverse (capital) order by modification time (so from oldest to newest like ls -rt)
  
  
  • 
    [1]: select first matching file only
  
  
  
  


• 
  -M file: gets the age of the content of the file.


• 
  0+ or 86400* force a conversion to number (for the undef case).