Does a check on the specified file.
flag- Flag may be one of the following:
d - Checks if the file is a directory.
e - Checks if the file exists.
f - Checks if the file is a regular file.
m - Returns the file mode (in octal)
s - Returns the size (in bytes) of the file
A - Returns the epoch at which the file was last accessed.
C - Returns the epoch at which the inode was last changed.
M - Returns the epoch at which the file was last modified.
This documentation was imported from Asterisk Version GIT-20-f8000daff5