Delete all but the most recent X files in bash

The problems with the existing answers:

• inability to handle filenames with embedded spaces or newlines.
  • in the case of solutions that invoke rm directly on an unquoted command substitution (rm `...`), there’s an added risk of unintended globbing.
• inability to distinguish between files and directories (i.e., if directories happened to be among the 5 most recently modified filesystem items, you’d effectively retain fewer than 5 files, and applying rm to directories will fail).

wnoise’s answer addresses these issues, but the solution is GNU-specific (and quite complex).

Here’s a pragmatic, POSIX-compliant solution that comes with only one caveat: it cannot handle filenames with embedded newlines – but I don’t consider that a real-world concern for most people.

^{For the record, here’s the explanation for why it’s generally not a good idea to parse ls output: http://mywiki.wooledge.org/ParsingLs}

ls -tp | grep -v '/$' | tail -n +6 | xargs -I {} rm -- {}

^{Note: This command operates in the current directory; to target a directory explicitly, use a subshell ((...)) with cd:
(cd /path/to && ls -tp | grep -v '/$' | tail -n +6 | xargs -I {} rm -- {})
The same applies analogously to the commands below.}

The above is inefficient, because xargs has to invoke rm separately for each filename.
However, your platform’s specific xargs implementation may allow you to solve this problem:

A solution that works with GNU xargs is to use -d '\n', which makes xargs consider each input line a separate argument, yet passes as many arguments as will fit on a command line at once:

ls -tp | grep -v '/$' | tail -n +6 | xargs -d '\n' -r rm --

^{Note: Option -r (--no-run-if-empty) ensures that rm is not invoked if there’s no input.}

A solution that works with both GNU xargs and BSD xargs (including on macOS) – though technically still not POSIX-compliant – is to use -0 to handle NUL-separated input, after first translating newlines to NUL (0x0) chars., which also passes (typically) all filenames at once:

ls -tp | grep -v '/$' | tail -n +6 | tr '\n' '\0' | xargs -0 rm --

Explanation:

• ls -tp prints the names of filesystem items sorted by how recently they were modified , in descending order (most recently modified items first) (-t), with directories printed with a trailing / to mark them as such (-p).

  • Note: It is the fact that ls -tp always outputs file / directory names only, not full paths, that necessitates the subshell approach mentioned above for targeting a directory other than the current one ((cd /path/to && ls -tp ...)).

• grep -v '/$' then weeds out directories from the resulting listing, by omitting (-v) lines that have a trailing / (/$).

  • Caveat: Since a symlink that points to a directory is technically not itself a directory, such symlinks will not be excluded.

• tail -n +6 skips the first 5 entries in the listing, in effect returning all but the 5 most recently modified files, if any.
  Note that in order to exclude N files, N+1 must be passed to tail -n +.

• xargs -I {} rm -- {} (and its variations) then invokes on rm on all these files; if there are no matches at all, xargs won’t do anything.

  • xargs -I {} rm -- {} defines placeholder {} that represents each input line as a whole, so rm is then invoked once for each input line, but with filenames with embedded spaces handled correctly.
  • -- in all cases ensures that any filenames that happen to start with - aren’t mistaken for options by rm.

A variation on the original problem, in case the matching files need to be processed individually or collected in a shell array:

# One by one, in a shell loop (POSIX-compliant):
ls -tp | grep -v '/$' | tail -n +6 | while IFS= read -r f; do echo "$f"; done

# One by one, but using a Bash process substitution (<(...), 
# so that the variables inside the `while` loop remain in scope:
while IFS= read -r f; do echo "$f"; done < <(ls -tp | grep -v '/$' | tail -n +6)

# Collecting the matches in a Bash *array*:
IFS=$'\n' read -d '' -ra files  < <(ls -tp | grep -v '/$' | tail -n +6)
printf '%s\n' "${files[@]}" # print array elements