Bash function to find newest file matching pattern

Question

In Bash  I would like to create a function that returns the filename of the newest file that matches a certain pattern   For example  I have a directory of files like   Directory     a1 1 5 1    a1 2 1 4    b2 1 0    b2 2 3 4    b2 3 2 0   I want the newest file that starts with  b2    How do I do this in bash   I need to have this in my    bash profile script

User · Answer

Use the find command   Assuming you re using Bash 4 2   use -printf   T   p n  for file timestamp value   find  DIR -type f -printf   T   p n    sort -r   head -n 1   cut -d    -f2   Example   find   Downloads -type f -printf   T   p n    sort -r   head -n 1   cut -d    -f2   For a more useful script  see the find-latest script here  https   github com l3x helpers

User · Answer

The ls command has a parameter -t to sort by time  You can then grab the first  newest  with head -1   ls -t b2    head -1   But beware  Why you shouldn t parse the output of ls  My personal opinion  parsing ls is only dangerous when the filenames can contain funny characters like spaces or newlines  If you can guarantee that the filenames will not contain funny characters then parsing ls is quite safe   If you are developing a script which is meant to be run by many people on many systems in many different situations then I very much do recommend to not parse ls   Here is how to do it  right   How can I find the latest  newest  earliest  oldest  file in a directory   unset -v latest for file in   dir     do       file -nt  latest     amp  amp  latest  file done

User · Answer

There is a much more efficient way of achieving this  Consider the following command   find   -cmin 1 -name  b2     This command finds the latest file produced exactly one minute ago with the wildcard search on  b2    If you want files from the last two days then you ll be better off using the command below   find   -mtime 2 -name  b2     The     represents the current directory   Hope this helps

User · Answer

You can use stat with a file glob and a decorate-sort-undecorate with the file time added on the front     stat -f   m t N  b2    sort -rn   head -1   cut -f2-

User · Answer

This is a possible implementation of the required Bash function     Print the newest file  if any  matching the given pattern   Example usage      newest matching file  b2     WARNING  Files whose names begin with a dot will not be checked function newest matching file         Use   1-  instead of  1 in case  nounset  is set     local -r glob pattern   1-       if          1      then         echo  usage  newest matching file GLOB PATTERN   gt  amp 2         return 1     fi        To avoid printing garbage if no files match the pattern  set        nullglob  if necessary     local -i need to unset nullglob 0     if       BASHOPTS        nullglob        then         shopt -s nullglob         need to unset nullglob 1     fi      newest file      for file in  glob pattern   do            -z  newest file     file -nt  newest file                   amp  amp  newest file  file     done        To avoid unexpected behaviour elsewhere  unset nullglob if it was       set by this function        need to unset nullglob     amp  amp  shopt -u nullglob        Use printf instead of echo in case the file name begins with  -         -n  newest file     amp  amp  printf   s n    newest file       return 0     It uses only Bash builtins  and should handle files whose names contain newlines or other unusual characters

User · Answer

The combination of find and ls works well for   filenames without newlines not very large amount of files not very long filenames   The solution   find   -name  my-pattern  -print0       xargs -r -0 ls -1 -t       head -1   Let s break it down   With find we can match all interesting files like this   find   -name  my-pattern        then using -print0 we can pass all filenames safely to the ls like this   find   -name  my-pattern  -print0   xargs -r -0 ls -1 -t   additional find search parameters and patterns can be added here  find   -name  my-pattern      -print0   xargs -r -0 ls -1 -t   ls -t will sort files by modification time  newest first  and print it one at a line  You can use -c to sort by creation time  Note  this will break with filenames containing newlines   Finally head -1 gets us the first file in the sorted list   Note  xargs use system limits to the size of the argument list  If this size exceeds  xargs will call ls multiple times  This will break the sorting and probably also the final output  Run   xargs  --show-limits   to check the limits on you system   Note 2  use find   -maxdepth 1 -name  my-pattern  -print0 if you don t want to search files through subfolders   Note 3  As pointed out by  starfry - -r argument for xargs is preventing the call of ls -1 -t  if no files were matched by the find  Thank you for the suggesion

User · Answer

Dark magic function incantation for those who want the find     xargs     head     solution above  but in easy to use function form so you don t have to think    define the function find newest file matching pattern under directory        echo   find  1 -name  2 -print0   xargs -0 ls -1 -t   head -1      setup   mkdir  tmp files to move  cd  tmp files to move  touch file1 txt  touch file2 txt   invoke the function  newest file    find newest file matching pattern under directory  tmp files to move  bc    echo  newest file   Prints   file2 txt   Which is   The filename with the oldest modified timestamp of the file under the given directory matching the given pattern

User · Answer

Unusual filenames  such as a file containing the valid  n character can wreak havoc with this kind of parsing  Here s a way to do it in Perl   perl -le   sorted   map    - gt  0                        sort   a- gt  1   lt   gt   b- gt  1                        map       -M                            ARGV            print  sorted 0    b2    That s a Schwartzian transform used there

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