String Functions

The most useful built-in string functions:

s = "  Julia is fast  "
t = strip(s)
println("[", t, "]")
println(uppercase(t), " | ", lowercase(t))
println(occursin("fast", t), " ", startswith(t, "Jul"), " ", endswith(t, "!"))
println(replace(t, "fast" => "fun"))
println(split("a,b,,c", ","))
println(join(["x", "y", "z"], " + "))
println(findfirst("is", t))
println(reverse("stressed"))

[Julia is fast]
JULIA IS FAST | julia is fast
true true false
Julia is fun
SubString{String}["a", "b", "", "c"]
x + y + z
7:8
desserts

• strip, lstrip, rstrip remove whitespace.
• occursin(needle, haystack) checks for a substring.
• replace(s, old => new) uses a pair (=>) for the replacement.
• split returns a vector of substrings; join does the reverse.
• findfirst returns the range of indices where the match starts and ends (or nothing).

Formatting numbers

The Printf standard library gives C-style formatting:

using Printf

price = 1234.5
@printf("Price: %.2f\n", price)
@printf("%-8s|%6d|\n", "apples", 42)
label = @sprintf("%05.1f%%", 7.26)
println(label)
println(lpad(7, 3, "0"), " ", rpad("ab", 5, "."), "|")

Price: 1234.50
apples  |    42|
007.3%
007 ab...|

• @printf prints; @sprintf returns a string.
• %.2f two decimals, %6d integer in 6 columns, %-8s left-aligned string, %% a literal percent sign.
• lpad and rpad pad a value to a width.

Regular expressions

Regexes are written r"...":

text = "Order 66 shipped on 2024-05-17, order 67 on 2024-06-02"
println(occursin(r"\d{4}-\d{2}-\d{2}", text))
m = match(r"(\d{4})-(\d{2})-(\d{2})", text)
println(m.match, " year=", m[1])
for m in eachmatch(r"order (\d+)"i, text)
    println("order number: ", m[1])
end
println(replace(text, r"\d{4}-\d{2}-\d{2}" => "<date>"))

true
2024-05-17 year=2024
order number: 66
order number: 67
Order 66 shipped on <date>, order 67 on <date>

The i after the closing quote makes the match case-insensitive. Test your patterns interactively with the regex tester.

Practice

Turn "the quick brown fox" into "The Quick Brown Fox" by splitting into words, capitalizing each, and joining them.

words = split("the quick brown fox")
println(join(uppercasefirst.(words), " "))

The Quick Brown Fox