| glob2rx {utils} | R Documentation |
Change Wildcard or Globbing Pattern into Regular Expression
Description
Change wildcard aka globbing patterns into the
corresponding regular expressions (regexp).
This is also a practical didactical example for the use of
sub() and regular expressions.
Usage
glob2rx(pattern, trim.head = FALSE, trim.tail = TRUE)
Arguments
pattern |
character vector |
trim.head |
logical specifying if leading |
trim.tail |
logical specifying if trailing |
Details
This takes a wildcard as used by most shells and returns an equivalent regular expression. ‘?’ is mapped to ‘.’ (match a single character), ‘*’ to ‘.*’ (match any string, including an empty one), and the pattern is anchored (it must start at the beginning and end at the end). Optionally, the resulting regexp is simplified.
Note that now even ‘(’, ‘[’ and ‘{’ can be used
in pattern, but glob2rx() may not work correctly with
arbitrary characters in pattern, for example escaped special
characters.
Value
A character vector of the same length as the input pattern
where each wildcard is translated to the corresponding
regular expression.
Author(s)
Martin Maechler, Unix/sed based version, 1991; current: 2004
See Also
regexp about regular expression,
sub, etc about substitutions using regexps.
Sys.glob does wildcard expansio, i.e., “globbing” on
file paths more subtly, e.g., allowing to escape special characters.
Examples
stopifnot(glob2rx("abc.*") == "^abc\\.",
glob2rx("a?b.*") == "^a.b\\.",
glob2rx("a?b.*", trim.tail = FALSE) == "^a.b\\..*$",
glob2rx("*.doc") == "^.*\\.doc$",
glob2rx("*.doc", trim.head = TRUE) == "\\.doc$",
glob2rx("*.t*") == "^.*\\.t",
glob2rx("*.t??") == "^.*\\.t..$",
glob2rx("*[*") == "^.*\\["
)