How to check if a file exists in Go

Question

Go s standard library does not have a function solely intended to check if a file exists or not  like Python s os path exists   What is the idiomatic way to do it

User · Answer

You should use the os Stat   and os IsNotExist   functions as in the following example      Exists reports whether the named file or directory exists  func Exists name string  bool       if    err    os Stat name   err    nil           if os IsNotExist err                return false                     return true     The example is extracted from here

User · Answer

To check if a file doesn t exist  equivalent to Python s if not os path exists filename    if    err    os Stat   path to whatever    os IsNotExist err         path to whatever does not exist     To check if a file exists  equivalent to Python s if os path exists filename    Edited  per recent comments  if    err    os Stat   path to whatever    err    nil        path to whatever exists    else if os IsNotExist err         path to whatever does  not  exist    else        Schrodinger  file may or may not exist  See err for details        Therefore  do  NOT  use  os IsNotExist err  to test for file existence

User · Answer

err    os Stat file      if err    nil           log Printf  file  s exists   file        else if os IsNotExist err            log Printf  file  s not exists   file        else           log Printf  file  s stat error   v   file  err

User · Answer

As mentioned in other answers  it is possible to construct the required behaviour   errors from using different flags with os OpenFile  In fact  os Create is just a sensible-defaults shorthand for doing so       Create creates or truncates the named file  If the file already exists     it is truncated  If the file does not exist  it is created with mode 0666     before umask   If successful  methods on the returned File can    be used for I O  the associated file descriptor has mode O RDWR     If there is an error  it will be of type  PathError  func Create name string    File  error        return OpenFile name  O RDWR O CREATE O TRUNC  0666      You should combine these flags yourself to get the behaviour you are interested in      Flags to OpenFile wrapping those of the underlying system  Not all    flags may be implemented on a given system  const          Exactly one of O RDONLY  O WRONLY  or O RDWR must be specified      O RDONLY int   syscall O RDONLY    open the file read-only      O WRONLY int   syscall O WRONLY    open the file write-only      O RDWR   int   syscall O RDWR      open the file read-write         The remaining values may be or ed in to control behavior      O APPEND int   syscall O APPEND    append data to the file when writing      O CREATE int   syscall O CREAT     create a new file if none exists      O EXCL   int   syscall O EXCL      used with O CREATE  file must not exist      O SYNC   int   syscall O SYNC      open for synchronous I O      O TRUNC  int   syscall O TRUNC     truncate regular writable file when opened      Depending on what you pick  you will get different errors   Here s an example where I wish to open a file for writing  but I will only truncate an existing file if the user has said that is OK   var f  os File if truncateWhenExists          O TRUNC - truncate regular writable file when opened      if f  err   os OpenFile filepath  os O RDWR os O CREATE os O TRUNC  0644   err    nil           log Fatalln  failed to force-open file  err    err          else          O EXCL - used with O CREATE  file must not exist     if f  err   os OpenFile filepath  os O RDWR os O CREATE os O EXCL  0644   err    nil           log Fatalln  failed to open file  err    err

User · Answer

The example by user11617 is incorrect  it will report that the file exists even in cases where it does not  but there was an error of some other sort   The signature should be Exists string   bool  error   And then  as it happens  the call sites are no better   The code he wrote would better as   func Exists name string  bool          err    os Stat name      return  os IsNotExist err      But I suggest this instead   func Exists name string   bool  error         err    os Stat name    if os IsNotExist err        return false  nil       return err    nil  err

User · Answer

The first thing to consider is that it is rare that you would only want to check whether or not a file exists  In most situations  you re trying to do something with the file if it exists  In Go  any time you try to perform some operation on a file that doesn t exist  the result should be a specific error  os ErrNotExist  and the best thing to do is check whether the return err value  e g  when calling a function like os OpenFile       is os ErrNotExist  The recommended way to do this used to be  file  err    os OpenFile      if os IsNotExist err           handle the case where the file doesn t exist    However  since the addition of errors Is in Go 1 13  released in late 2019   the new recommendation is to use errors Is  file  err    os OpenFile      if errors Is err  os ErrNotExist           handle the case where the file doesn t exist     It s usually best to avoid using os Stat to check for the existence of a file before you attempt to do something with it  because it will always be possible for the file to be renamed  deleted  etc  in the window of time before you do something with it  However  if you re OK with this caveat and you really  truly just want to check whether a file exists without then proceeding to do something useful with it  as a contrived example  let s say that you re writing a pointless CLI tool that tells you whether or not a file exists and then exits               then the recommended way to do it would be  if    err    os Stat filename   errors Is err  os ErrNotExist           file does not exist   else          file exists

User · Answer

Answer by Caleb Spare posted in gonuts mailing list            It s not actually needed very often and       using os Stat is    easy enough for the cases where it is required              For instance  if you are going to open the file  there s no reason to check whether it exists first  The file could disappear in between checking and opening  and anyway you ll need to check the os Open error regardless  So you simply call os IsNotExist err  after you try    to open the file  and deal with its non-existence there  if that requires special handling               You don t need to check for the paths existing at all  and you shouldn t            os MkdirAll works whether or not the paths already exist   Also you need to check the error from that call      Instead of using os Create  you should use os OpenFile path  os O RDWR os O CREATE os O EXCL  0666    That way you ll get an error if the file already exists  Also this doesn t have a race condition with something else making the file  unlike your version which checks for existence beforehand        Taken from  https   groups google com forum   msg golang-nuts Ayx-BMNdMFo 4rL8FFHr8v4J

User · Answer

Best way to check if file exists   if    err    os Stat   path to file    err    nil    os IsExist err           your code here if file exists

User · Answer

The function example   func file is exists f string  bool          err    os Stat f      if os IsNotExist err            return false           return err    nil

User · Answer

basicly  package main  import        quot fmt quot       quot os quot     func fileExists path string  bool          err    os Stat path      return  os IsNotExist err     func main          var file string    quot foo txt quot      exist    fileExists file           if exist           fmt Println  quot file exist quot         else            fmt Println  quot file not exists quot              run example other way with os Open package main  import        quot fmt quot       quot os quot     func fileExists path string  bool          err    os Open path     For read access      return err    nil     func main          fmt Println fileExists  quot d4d txt quot          run it

User · Answer

Let s look at few aspects first  both the function provided by os package of golang are not utilities but error checkers  what do I mean by that is they are just a wrapper to handle errors on cross platform   So basically if os Stat if this function doesn t give any error that means the file is existing if it does you need to check what kind of error it is  here comes the use of these two function os IsNotExist and os IsExist   This can be understood as the Stat of the file throwing error because it doesn t exists or is it throwing error because it exist and there is some problem with it   The parameter that these functions take is of type error  although you might be able to pass nil to it but it wouldn t make sense   This also points to the fact that IsExist is not same as  IsNotExist  they are way two different things   So now if you want to know if a given file exist in go  I would prefer the best way is   if    err    os Stat path to file    os IsNotExist err        TODO

User · Answer

What other answers missed  is that the path given to the function could actually be a directory  Following function makes sure  that the path is really a file   func fileExists filename string  bool       info  err    os Stat filename      if os IsNotExist err            return false           return  info IsDir        Another thing to point out  This code could still lead to a race condition  where another thread or process deletes or creates the specified file  while the fileExists function is running   If you re worried about this  use a lock in your threads  serialize the access to this function or use an inter-process semaphore if multiple applications are involved  If other applications are involved  outside of your control  you re out of luck  I guess

[file] How to check if a file exists in Go?

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