R functions: sub and gsub

sub (regexp, txtReplace, vec); # Replace first occurence
gsub(regexp, txtReplace, vec); # Replace all occurences

text    <- 'foo 42 bar 123 baz'
pattern <- '\\d+'
repl    <- ''

sub(pattern, repl, text)
# [1] "foo  bar 123 baz"

pattern <- '.*(\\d+).*'
repl    <- '\\1'
sub(pattern, repl, text)
# [1] "3"

pattern <- '.* (\\d+).*'
repl    <- '\\1'
sub(pattern, repl, text)
# [1] "123"

# non greedy:
pattern <- '.*? (\\d+).*'
repl    <- '\\1'
sub(pattern, repl, text)
# [1] "42"

gsub("xyz", "bar", "foo xyz baz xyz")
# [1] "foo bar baz bar"

# Note the regular expression (^)
gsub("^xyz", "bar", "foo xyz baz abcxyz")
# [1] "foo xyz baz abcxyz"

gsub("xyz", "bar", c("foo", "xyz", "baz"))
# [1] "foo" "bar" "baz"