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FileSize

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description

FileSize["name"]

gives the number of bytes in the file with the specified name.

Notes In FileSize\["name"\], name is interpreted relative to your current directory. FileSize does not search $Path. FileSize follows symbolic links, reporting the size of the target file. FileSize gives the size as an integer count of bytes, not a Quantity. FileSize returns $Failed and prints a message if the file cannot be found.

Examples (8)

Every input below was run against the current Mathilda build and its output recorded.

Basic Examples (4)

Writes "2\n3\n5\n7\n11\n" = 11 bytes

In[1]:= Put[2, 3, 5, 7, 11, "/tmp/mathilda_io_fs.txt"]

In[2]:= FileSize["/tmp/mathilda_io_fs.txt"]
Out[2]= 11

A plain Integer, not a Quantity

In[3]:= Head[FileSize["/tmp/mathilda_io_fs.txt"]]
Out[3]= Integer

Missing file -> $Failed

In[4]:= Quiet[FileSize["/tmp/mathilda_no_such_file_xyz"]]
Out[4]= $Failed

Applications (4)

Writes "2\n3\n5\n7\n11\n" = 11 bytes

In[5]:= Put[2, 3, 5, 7, 11, "/tmp/mathilda_fs.txt"];

In[6]:= FileSize["/tmp/mathilda_fs.txt"]
Out[6]= 11

A plain Integer, not a Quantity

In[7]:= Put[2, 3, 5, 7, 11, "/tmp/mathilda_fs.txt"]; Head[FileSize["/tmp/mathilda_fs.txt"]]
Out[7]= Integer

Missing file -> $Failed

In[8]:= Quiet[FileSize["/tmp/mathilda_no_such_file_xyz"]]
Out[8]= $Failed

Implementation notes

Algorithm. builtin_filesize accepts exactly one EXPR_STRING argument (anything else — wrong arity, a symbol, a non-string atom — returns NULL, leaving the call unevaluated so symbolic arguments flow through). It calls stat() on the path and, on success, returns st.st_size as an Integer (expr_new_integer((int64_t)st.st_size)) — a plain byte count, not a Quantity. stat (not lstat) follows symbolic links, so the size reported is the target file's.

When the path cannot be stat'd (most often because nothing is there) it emits FileSize::nffil through fs_msg and returns $Failed. fs_msg is the local diagnostic funnel: it calls mth_msg_note_fired() (so Check[] sees the message) and returns early under mth_msg_suppressed() (so Quiet[] silences it), then vfprintfs to stderr — the same Quiet/Check-aware pattern as dt_msg in src/datetime.c.

Data structures. None beyond a struct stat; the path is read directly out of the argument string. _POSIX_C_SOURCE 200809L is defined before any include so stat is visible under glibc's -std=c99 (SPEC.md §10).

Complexity / limits. O(1) — one stat syscall. The path is interpreted relative to the current working directory; $Path is not searched. ATTR_PROTECTED.

  • Protected.
  • "name" is interpreted relative to the current working directory. $Path is not searched.
  • Implemented with stat(), so symbolic links are followed and the target file's size is reported.
  • Returns $Failed and prints a FileSize::nffil message when the file cannot be found. The message respects Quiet[] and is visible to Check[].
  • Leaves the call unevaluated when given the wrong arity, a symbolic argument, or any non-string atom.

Attributes: Protected.

References

Notes & additional examples

Notes

FileSize["name"] gives the file's size in bytes as a plain Integer (not a Quantity). The path is relative to the current working directory; $Path is not searched. It is implemented with stat, so a symbolic link is followed and the target file's size is reported.

A path that cannot be stat'd (usually because nothing is there) returns $Failed with a FileSize::nffil message, which respects Quiet[] and is visible to Check[]. A symbolic or non-string argument leaves the call unevaluated.