Rename all files in a directory according to a pattern (regular expression)

batch.rename.file <- function(pattern, replacement, path=".")
{ 
    ## Purpose: Rename all files in a directory according to a pattern (regular expression). 
    ## Arguments:
    ##   pattern: a regular expression (as is used by R base function "sub") to match the file names. 
    ##   replacement: replacement text for the new file name (as is used by R base function "gsub")
    ##   path: path to a directory containing the files to be renamed.  Default to the current directory. 
    ## Return: Side Effect (all files in the directory will be renamed)
    ## Author: Feiming Chen, Date: 21 Apr 2017, 13:32
    ## ________________________________________________
    
    f1 <- dir(path, pattern, full.names = T, recursive = T) # Current file names. Include all files in subdirectories. 
    f1.base <- basename(f1)
    f2.base <-  sub(pattern, replacement, f1.base)                   # Corresponding New file names
    f2 <- file.path(dirname(f1), f2.base)
    ans <- file.rename(f1, f2)
    idx <- which(!ans)                  # which operation (file renaming) fails
    if (length(idx) == 0) {
        cat("All", length(ans), "files are renamed.\n")
    } else {
        cat(length(idx), "out of", length(ans), "files are not renamed.\n")
    }
}
if (F) {                                # Unit Test
    dir.create("tmp")
    setwd("tmp")
    file.create("a.b.html", "c.d.html")
    batch.rename.file("\\.", "_")
    dir()                               # "a_b.html" "c_d.html"
}