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C Library Functions  - scratch (3)

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NAME

scratch(3f) - [M_io:QUERY] Return the name of a scratch file (LICENSE:PD)

CONTENTS

Synopsis
Description
Options
Returns
Examples
Author
License

SYNOPSIS

function scratch(prefix) result(tname)

     character(len=:),allocatable         :: tname
     character(len=*),intent(in),optional :: prefix

DESCRIPTION

Fortran supports non-retainable automatically deleted scratch files via OPEN(STATUS=’SCRATCH’,...). However, there are circumstances where a file with a unique name is required instead.

Specifying the pathname of a file can be required for performance reasons, file space limitations, or to support the ability for other processes or subprocesses to access the file.

By default SCRATCH(3f) Returns a unique filename for a scratch file in the directory pointed to by the most common environment variables used to designate a scratch directory.

The environment variables queried are $TMPDIR (the canonical environment variable in Unix and POSIX used to specify a temporary directory for scratch space) . If $TMPDIR is not set, $TEMP, $TEMPDIR, and $TMP are examined in that order. If nothing is set "/tmp/" is used.

OPTIONS

prefix

an optional prefix for the leaf of the filename. The prefix is used as-is if it contains the character "/" or "\". A suffix created by genuuid(3) is used to make the name unique. Otherwise, the prefix is prefixed by the first value that is not blank from the set {$TMPDIR, $TEMP, $TEMPDIR, $TMP, /tmp}. The default prefix is the basename of the program that called the procedure (the name trimmed of directories and anything from the right-most period in the name to the end of the name).

RETURNS

o	If a prefix is not supplied:

      a filename whose basename is the current program followed by a UUID
      ( Universal Unique IDentifier) with the prefix ".scr" in the current
      temporary directory.

o	if the prefix contains a slash or backslash:

      The same as if a prefix is not supplied accept the prefix is assumed to
      be a directory in which to create a file

o	A prefix not containing a slash or backslash:

      The same as if a prefix is not supplied accept the basename begins with
      the given string instead of the current program name.

EXAMPLES

Sample:

    program demo_scratch
    use M_io, only : scratch
    implicit none
    write(*,*)’find good scratch file name candidates; one should test if writable’
    call printit(’JUNK:’)
    call printit(’./’)
    call printit(’/var/tmp/’)
    call printit(’’)
    call printit()
    contains
    subroutine printit(NAME)
    character(len=*),intent(in),optional :: NAME
    if(present(NAME))then
       write(*,’(a,t20,a)’)NAME,scratch(NAME)
    else
       write(*,’(a,t20,a)’)’*OT PRESENT*’,scratch()
    endif
    end subroutine printit
    end program demo_scratch

Results:

   >  find good scratch file name candidates; one should test if writable
   > JUNK:              /tmp/JUNK:405d766e-1320-4405-50e1-5d88fffbee9a.scr
   > ./                 ./xx-901606b1-6ad2-4e96-6b17-e8bffedf2452.scr
   > /var/tmp/          /var/tmp/xx-3f5c55fa-17ca-4020-4a05-a9d9cfad8dbe.scr
   >                    /tmp/f10e0491-a2ff-4455-5ff6-55d7dfe7fa8c.scr
   > *NOT PRESENT*      /tmp/xx-f4fed5f7-3694-4609-5af4-8902ffa75839.scr

AUTHOR

John S. Urban

LICENSE

Public Domain

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Nemo Release 3.1

scratch (3)

February 23, 2025

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