How can I find the latest (newest, earliest, oldest) file in a directory?

The tempting solution is to use ls to output sorted filenames and take the first result. As usual, the ls approach cannot be made robust and should never be used in scripts due in part to the possibility of arbitrary characters (including newlines) present in filenames. Therefore, we need some other way to compare file metadata.

The most common requirement is to get the most or least recently modified files in a directory. Bash and all ksh variants can compare modification times (mtime) using the -nt and -ot operators of the conditional expression compound command:

# Bash/ksh
unset -v latest
for file in "$dir"/*; do
  [[ $file -nt $latest ]] && latest=$file
done

Or to find the oldest:

# Bash/ksh
unset -v oldest
for file in "$dir"/*; do
  [[ -z $oldest || $file -ot $oldest ]] && oldest=$file
done

Keep in mind that mtime on directories is that of the most recently added, removed, or renamed file in that directory. Also note that -nt and -ot are not specified by POSIX test, however many shells such as dash include them anyway. No bourne-like shell has analogous operators for comparing by atime or ctime, so one would need external utilities for that; however, it's nearly impossible to either produce output which can be safely parsed, or handle said output in a shell without using nonstandard features on both ends.

If the sorting criteria are different from "oldest or newest file by mtime", then GNU find and GNU sort may be used together to produce a sorted list of filenames + timestamps, delimited by NUL characters. This will of course operate recursively (GNU find's -maxdepth operator can prevent that); Here are a few possibilities, which can be modified as necessary to use atime or ctime, or to sort in reverse order:

# Bash + GNU find + GNU sort (To the precision possible on the given OS, but returns only one result)
IFS= read -r -d '' latest \
  < <(find "$dir" -type f -printf '%T@ %p\0' | sort -znr)
latest=${latest#* }   # remove timestamp + space

# GNU find + Bash w/ arrays (To the nearest 1s, using an undocumented "find -printf" format (%Ts).)
while IFS= read -rd '' 'latest[$(read -rd "" y; echo $y)]'
    do :
done < <(find "$dir" -type f -printf '%p\0%Ts\0')
latest=${latest[-1]}

# GNU stat + Bash /w arrays (non-recursive w/o globstar, to the nearest 1s)
while IFS= read -rd '' 'latest[$(read -rd "" y; echo $y)]'
    do :
done < <(stat '--printf=%n\0%Y\0' "$dir"/*)
latest=${latest[-1]}

One disadvantage to these approaches is that the entire list is sorted, whereas simply iterating through the list to find the minimum or maximum timestamp (assuming we want just one file) would be faster, however, depending on the size of the job the algorithmic disadvantage of sorting may be negligible in comparison to the overhead of using a shell.

# Bash + GNU find
unset -v latest time
while IFS= read -r -d '' line; do
  t=${line%% *} t=${t%.*}   # truncate fractional seconds
  ((t > time)) && { latest=${line#* } time=$t; }
done < <(find "$dir" -type f -printf '%T@ %p\0')

Lastly, here's a more verbose variant for use in a library or .bashrc which can either return a result or assign directly to a variable:

latest() {
    if [[ $FUNCNAME == ${FUNCNAME[1]} ]]; then
        unset -v x latest
        printf ${2:+'-v' "$2"} '%s' "$1"
        return
    fi

    if (($# > 2)); then
        echo $'Usage: latest <glob> <varname>\nError: Takes at most 2 arguments. Glob defaults to *'
        return 1
    fi >&2

    if ! shopt -q nullglob; then
        trap 'shopt -u nullglob; trap - RETURN' RETURN
        shopt -s nullglob
    fi

    local x latest

    for x in ${1-*}; do
        [[ -d $x || $x -nt $latest ]] && latest=$x
    done

    latest "$latest" ${2+"$2"}
}

Readers who are asking this question in order to rotate their log files may wish to look into logrotate(1) instead, if their operating system provides it.

CategoryShell