diff --git a/NEWS.md b/NEWS.md
index c12cc3c64300c..37edaa843a17e 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -103,6 +103,7 @@ New library features
 * `RegexMatch` objects can now be used to construct `NamedTuple`s and `Dict`s ([#50988])
 * `Lockable` is now exported ([#54595])
 * New `ltruncate`, `rtruncate` and `ctruncate` functions for truncating strings to text width, accounting for char widths ([#55351])
+* `takestring!(v)` creates a `String` from `v` (a `Vector{UInt8}` or `IOBuffer`), truncating `v` and reusing its memory if possible )([#54372]).
 
 Standard library changes
 ------------------------
diff --git a/base/compiler/ssair/show.jl b/base/compiler/ssair/show.jl
index 7d936a1688aba..53799e980462b 100644
--- a/base/compiler/ssair/show.jl
+++ b/base/compiler/ssair/show.jl
@@ -312,7 +312,7 @@ function compute_ir_line_annotations(code::IRCode)
             loc_method = string(" "^printing_depth, loc_method)
             last_stack = stack
         end
-        push!(loc_annotations, String(take!(buf)))
+        push!(loc_annotations, takestring!(buf))
         push!(loc_lineno, (lineno != 0 && lineno != last_lineno) ? string(lineno) : "")
         push!(loc_methods, loc_method)
         (lineno != 0) && (last_lineno = lineno)
diff --git a/base/errorshow.jl b/base/errorshow.jl
index a3bf464439d44..1454193a11393 100644
--- a/base/errorshow.jl
+++ b/base/errorshow.jl
@@ -305,7 +305,7 @@ function showerror(io::IO, ex::MethodError)
         iob = IOContext(buf, io)     # for type abbreviation as in #49795; some, like `convert(T, x)`, should not abbreviate
         show_signature_function(iob, Core.Typeof(f))
         show_tuple_as_call(iob, :function, arg_types; hasfirst=false, kwargs = isempty(kwargs) ? nothing : kwargs)
-        str = String(take!(buf))
+        str = takestring!(buf)
         str = type_limited_string_from_context(io, str)
         print(io, str)
     end
@@ -596,7 +596,7 @@ function show_method_candidates(io::IO, ex::MethodError, kwargs=[])
             m = parentmodule_before_main(method)
             modulecolor = get!(() -> popfirst!(STACKTRACE_MODULECOLORS), STACKTRACE_FIXEDCOLORS, m)
             print_module_path_file(iob, m, string(file), line; modulecolor, digit_align_width = 3)
-            push!(lines, String(take!(buf)))
+            push!(lines, takestring!(buf))
             push!(line_score, -(right_matches * 2 + (length(arg_types_param) < 2 ? 1 : 0)))
         end
     end
diff --git a/base/exports.jl b/base/exports.jl
index daba9a010a9e6..b1eda2b60c52c 100644
--- a/base/exports.jl
+++ b/base/exports.jl
@@ -638,6 +638,7 @@ export
     split,
     string,
     strip,
+    takestring!,
     textwidth,
     thisind,
     titlecase,
diff --git a/base/filesystem.jl b/base/filesystem.jl
index bc1f4942877e8..9a5256f2d6478 100644
--- a/base/filesystem.jl
+++ b/base/filesystem.jl
@@ -141,7 +141,7 @@ import .Base:
     bytesavailable, position, read, read!, readavailable, seek, seekend, show,
     skip, stat, unsafe_read, unsafe_write, write, transcode, uv_error,
     setup_stdio, rawhandle, OS_HANDLE, INVALID_OS_HANDLE, windowserror, filesize,
-    isexecutable, isreadable, iswritable, MutableDenseArrayType
+    isexecutable, isreadable, iswritable, MutableDenseArrayType, unsafe_takestring!
 
 import .Base.RefValue
 
diff --git a/base/gmp.jl b/base/gmp.jl
index 1eaa20d6baecf..df0d9fee49348 100644
--- a/base/gmp.jl
+++ b/base/gmp.jl
@@ -11,7 +11,7 @@ import .Base: *, +, -, /, <, <<, >>, >>>, <=, ==, >, >=, ^, (~), (&), (|), xor,
              bin, oct, dec, hex, isequal, invmod, _prevpow2, _nextpow2, ndigits0zpb,
              widen, signed, unsafe_trunc, trunc, iszero, isone, big, flipsign, signbit,
              sign, hastypemax, isodd, iseven, digits!, hash, hash_integer, top_set_bit,
-             clamp
+             clamp, unsafe_takestring
 
 if Clong == Int32
     const ClongMax = Union{Int8, Int16, Int32}
@@ -761,7 +761,7 @@ function string(n::BigInt; base::Integer = 10, pad::Integer = 1)
         sv[i] = '0' % UInt8
     end
     isneg(n) && (sv[1] = '-' % UInt8)
-    String(sv)
+    unsafe_takestring(sv)
 end
 
 function digits!(a::AbstractVector{T}, n::BigInt; base::Integer = 10) where {T<:Integer}
diff --git a/base/indices.jl b/base/indices.jl
index 455bb0f7656a1..4253755d552a5 100644
--- a/base/indices.jl
+++ b/base/indices.jl
@@ -132,7 +132,7 @@ function throw_promote_shape_mismatch(a::Tuple, b::Union{Nothing,Tuple}, i = not
     if i ≢ nothing
         print(msg, ", mismatch at dim ", i)
     end
-    throw(DimensionMismatch(String(take!(msg))))
+    throw(DimensionMismatch(takestring!(msg)))
 end
 
 function promote_shape(a::Tuple{Int,}, b::Tuple{Int,})
diff --git a/base/int.jl b/base/int.jl
index a25b17e2cc958..581a875af4253 100644
--- a/base/int.jl
+++ b/base/int.jl
@@ -718,7 +718,7 @@ macro big_str(s)
             is_prev_dot = (c == '.')
         end
         print(bf, s[end])
-        s = String(take!(bf))
+        s = unsafe_takestring!(bf)
     end
     n = tryparse(BigInt, s)
     n === nothing || return n
diff --git a/base/intfuncs.jl b/base/intfuncs.jl
index 8d46fcffa3ad5..1515c2f763d7e 100644
--- a/base/intfuncs.jl
+++ b/base/intfuncs.jl
@@ -766,7 +766,7 @@ function bin(x::Unsigned, pad::Int, neg::Bool)
         i -= 1
     end
     neg && (@inbounds a[1] = 0x2d) # UInt8('-')
-    String(a)
+    unsafe_takestring(a)
 end
 
 function oct(x::Unsigned, pad::Int, neg::Bool)
@@ -780,7 +780,7 @@ function oct(x::Unsigned, pad::Int, neg::Bool)
         i -= 1
     end
     neg && (@inbounds a[1] = 0x2d) # UInt8('-')
-    String(a)
+    unsafe_takestring(a)
 end
 
 # 2-digit decimal characters ("00":"99")
@@ -850,7 +850,7 @@ function dec(x::Unsigned, pad::Int, neg::Bool)
     a = StringMemory(n)
     append_c_digits_fast(n, x, a, 1)
     neg && (@inbounds a[1] = 0x2d) # UInt8('-')
-    String(a)
+    unsafe_takestring(a)
 end
 
 function hex(x::Unsigned, pad::Int, neg::Bool)
@@ -871,7 +871,7 @@ function hex(x::Unsigned, pad::Int, neg::Bool)
         @inbounds a[i] = d + ifelse(d > 0x9, 0x57, 0x30)
     end
     neg && (@inbounds a[1] = 0x2d) # UInt8('-')
-    String(a)
+    unsafe_takestring(a)
 end
 
 const base36digits = UInt8['0':'9';'a':'z']
@@ -896,7 +896,7 @@ function _base(base::Integer, x::Integer, pad::Int, neg::Bool)
         i -= 1
     end
     neg && (@inbounds a[1] = 0x2d) # UInt8('-')
-    String(a)
+    unsafe_takestring(a)
 end
 
 split_sign(n::Integer) = unsigned(abs(n)), n < 0
@@ -972,7 +972,7 @@ function bitstring(x::T) where {T}
         x = lshr_int(x, 4)
         i -= 4
     end
-    return String(str)
+    return unsafe_takestring(str)
 end
 
 """
diff --git a/base/io.jl b/base/io.jl
index 83a215d6359fc..9e0308cffd653 100644
--- a/base/io.jl
+++ b/base/io.jl
@@ -277,13 +277,13 @@ julia> io = IOBuffer();
 julia> write(io, "JuliaLang is a GitHub organization.", " It has many members.")
 56
 
-julia> String(take!(io))
+julia> takestring!(io)
 "JuliaLang is a GitHub organization. It has many members."
 
 julia> write(io, "Sometimes those members") + write(io, " write documentation.")
 44
 
-julia> String(take!(io))
+julia> takestring!(io)
 "Sometimes those members write documentation."
 ```
 User-defined plain-data types without `write` methods can be written when wrapped in a `Ref`:
@@ -544,7 +544,7 @@ julia> rm("my_file.txt")
 """
 readuntil(filename::AbstractString, delim; kw...) = open(io->readuntil(io, delim; kw...), convert(String, filename)::String)
 readuntil(stream::IO, delim::UInt8; kw...) = _unsafe_take!(copyuntil(IOBuffer(sizehint=16), stream, delim; kw...))
-readuntil(stream::IO, delim::Union{AbstractChar, AbstractString}; kw...) = String(_unsafe_take!(copyuntil(IOBuffer(sizehint=16), stream, delim; kw...)))
+readuntil(stream::IO, delim::Union{AbstractChar, AbstractString}; kw...) = takestring!(copyuntil(IOBuffer(sizehint=16), stream, delim; kw...))
 readuntil(stream::IO, delim::T; keep::Bool=false) where T = _copyuntil(Vector{T}(), stream, delim, keep)
 
 
@@ -566,10 +566,10 @@ Similar to [`readuntil`](@ref), which returns a `String`; in contrast,
 ```jldoctest
 julia> write("my_file.txt", "JuliaLang is a GitHub organization.\\nIt has many members.\\n");
 
-julia> String(take!(copyuntil(IOBuffer(), "my_file.txt", 'L')))
+julia> takestring!(copyuntil(IOBuffer(), "my_file.txt", 'L'))
 "Julia"
 
-julia> String(take!(copyuntil(IOBuffer(), "my_file.txt", '.', keep = true)))
+julia> takestring!(copyuntil(IOBuffer(), "my_file.txt", '.', keep = true))
 "JuliaLang is a GitHub organization."
 
 julia> rm("my_file.txt")
@@ -616,8 +616,7 @@ Logan
 """
 readline(filename::AbstractString; keep::Bool=false) =
     open(io -> readline(io; keep), filename)
-readline(s::IO=stdin; keep::Bool=false) =
-    String(_unsafe_take!(copyline(IOBuffer(sizehint=16), s; keep)))
+readline(s::IO=stdin; keep::Bool=false) = takestring!(copyline(IOBuffer(sizehint=16), s; keep))
 
 """
     copyline(out::IO, io::IO=stdin; keep::Bool=false)
@@ -642,10 +641,10 @@ See also [`copyuntil`](@ref) for reading until more general delimiters.
 ```jldoctest
 julia> write("my_file.txt", "JuliaLang is a GitHub organization.\\nIt has many members.\\n");
 
-julia> String(take!(copyline(IOBuffer(), "my_file.txt")))
+julia> takestring!(copyline(IOBuffer(), "my_file.txt"))
 "JuliaLang is a GitHub organization."
 
-julia> String(take!(copyline(IOBuffer(), "my_file.txt", keep=true)))
+julia> takestring!(copyline(IOBuffer(), "my_file.txt", keep=true))
 "JuliaLang is a GitHub organization.\\n"
 
 julia> rm("my_file.txt")
@@ -1291,7 +1290,7 @@ function iterate(r::Iterators.Reverse{<:EachLine}, state)
         buf.size = _stripnewline(r.itr.keep, buf.size, buf.data)
         empty!(chunks) # will cause next iteration to terminate
         seekend(r.itr.stream) # reposition to end of stream for isdone
-        s = String(_unsafe_take!(buf))
+        s = unsafe_takestring!(buf)
     else
         # extract the string from chunks[ichunk][inewline+1] to chunks[jchunk][jnewline]
         if ichunk == jchunk # common case: current and previous newline in same chunk
@@ -1308,7 +1307,7 @@ function iterate(r::Iterators.Reverse{<:EachLine}, state)
             end
             write(buf, view(chunks[jchunk], 1:jnewline))
             buf.size = _stripnewline(r.itr.keep, buf.size, buf.data)
-            s = String(_unsafe_take!(buf))
+            s = unsafe_takestring!(buf)
 
             # overwrite obsolete chunks (ichunk+1:jchunk)
             i = jchunk
diff --git a/base/iobuffer.jl b/base/iobuffer.jl
index c0c2731eec08b..6e3e1ea30b671 100644
--- a/base/iobuffer.jl
+++ b/base/iobuffer.jl
@@ -66,7 +66,7 @@ julia> io = IOBuffer();
 julia> write(io, "JuliaLang is a GitHub organization.", " It has many members.")
 56
 
-julia> String(take!(io))
+julia> takestring!(io)
 "JuliaLang is a GitHub organization. It has many members."
 
 julia> io = IOBuffer(b"JuliaLang is a GitHub organization.")
@@ -84,7 +84,7 @@ IOBuffer(data=UInt8[...], readable=true, writable=true, seekable=true, append=fa
 julia> write(io, "JuliaLang is a GitHub organization.")
 34
 
-julia> String(take!(io))
+julia> takestring!(io)
 "JuliaLang is a GitHub organization"
 
 julia> length(read(IOBuffer(b"data", read=true, truncate=false)))
@@ -489,6 +489,84 @@ function take!(io::IOBuffer)
     return data
 end
 
+"Internal method. This method can be faster than takestring!, because it does not
+reset the buffer to a usable state, and it does not check for io.reinit.
+Using the buffer after calling unsafe_takestring! may cause undefined behaviour.
+This function is meant to be used when the buffer is only used as a temporary
+string builder, which is discarded after the string is built."
+function unsafe_takestring!(io::IOBuffer)
+    start = io.seekable ? io.offset + 1 : io.ptr
+    nbytes = io.size - start + 1
+    iszero(nbytes) && return ""
+    # The C function can only copy from the start of the memory.
+    # Fortunately, in most cases, the offset will be zero.
+    return if isone(start)
+        ccall(:jl_genericmemory_to_string, Ref{String}, (Any, Int), io.data, nbytes)
+    else
+        mem = StringMemory(nbytes)
+        unsafe_copyto!(mem, 1, io.data, start, nbytes)
+        unsafe_takestring(mem)
+    end
+end
+
+"""
+    takestring!(io::IOBuffer) -> String
+
+Return the content of `io` as a `String`, resetting the buffer to its initial
+state.
+This is preferred over calling `String(take!(io))` to create a string from
+an `IOBuffer`.
+
+# Examples
+```jldoctest
+julia> io = IOBuffer();
+
+julia> write(io, [0x61, 0x62, 0x63]);
+
+julia> s = takestring!(io)
+"abc"
+
+julia> isempty(take!(io)) # io is now empty
+true
+```
+
+!!! compat "Julia 1.12"
+    This function requires at least Julia 1.12.
+"""
+function takestring!(io::IOBuffer)
+    # If the buffer has been used up and needs to be replaced, there are no bytes, and
+    # we can return an empty string without interacting with the buffer at all.
+    io.reinit && return ""
+
+    # If the buffer is not writable, it may hold external memory the user has a
+    # reference to. We can't use unsafe_takestring! because the GC would take control
+    # of the memory and could deallocate it while the user still has a reference to it.
+    if !io.writable
+        nbytes = filesize(io)
+        return copyto!(StringVector(nbytes), 1, io.data, io.offset + 1, nbytes)
+    end
+    
+    s = unsafe_takestring!(io)
+
+    # Restore the buffer to a usable state, making it no longer undefined behaviour to
+    # use the buffer after the `unsafe_takestring!` call.
+    # Note that if the buffer is not writable, there is no need to reinitialize the buffer,
+    # since it doesn't matter that the returned string looks into the same memory -
+    # this is because the buffer is not mutable through either the string nor the buffer.
+    if io.writable
+        io.reinit = true
+        io.mark = -1
+        io.ptr = 1
+        io.size = 0
+        io.offset = 0
+    end
+    s
+end
+
+# Fallback methods
+unsafe_takestring!(io::GenericIOBuffer) = takestring!(io)
+takestring!(io::GenericIOBuffer) = String(take!(io))
+
 """
     _unsafe_take!(io::IOBuffer)
 
diff --git a/base/iostream.jl b/base/iostream.jl
index 762f881cfbecb..767ef8ba882c2 100644
--- a/base/iostream.jl
+++ b/base/iostream.jl
@@ -98,7 +98,7 @@ julia> write(io, "JuliaLang is a GitHub organization.")
 julia> truncate(io, 15)
 IOBuffer(data=UInt8[...], readable=true, writable=true, seekable=true, append=false, size=15, maxsize=Inf, ptr=16, mark=-1)
 
-julia> String(take!(io))
+julia> takestring!(io)
 "JuliaLang is a "
 
 julia> io = IOBuffer();
@@ -107,7 +107,7 @@ julia> write(io, "JuliaLang is a GitHub organization.");
 
 julia> truncate(io, 40);
 
-julia> String(take!(io))
+julia> takestring!(io)
 "JuliaLang is a GitHub organization.\\0\\0\\0\\0\\0"
 ```
 """
@@ -456,7 +456,7 @@ function readuntil_string(s::IOStream, delim::UInt8, keep::Bool)
 end
 readuntil(s::IOStream, delim::AbstractChar; keep::Bool=false) =
     isascii(delim) ? readuntil_string(s, delim % UInt8, keep) :
-    String(_unsafe_take!(copyuntil(IOBuffer(sizehint=70), s, delim; keep)))
+    takestring!(copyuntil(IOBuffer(sizehint=70), s, delim; keep))
 
 function readline(s::IOStream; keep::Bool=false)
     @_lock_ios s ccall(:jl_readuntil, Ref{String}, (Ptr{Cvoid}, UInt8, UInt8, UInt8), s.ios, '\n', 1, keep ? 0 : 2)
diff --git a/base/logging/ConsoleLogger.jl b/base/logging/ConsoleLogger.jl
index c4596dd86c3f5..c0a98822b52d4 100644
--- a/base/logging/ConsoleLogger.jl
+++ b/base/logging/ConsoleLogger.jl
@@ -141,7 +141,7 @@ function handle_message(logger::ConsoleLogger, level::LogLevel, message, _module
         for (key, val) in kwargs
             key === :maxlog && continue
             showvalue(valio, val)
-            vallines = split(String(take!(valbuf)), '\n')
+            vallines = split(takestring!(valbuf), '\n')
             if length(vallines) == 1
                 push!(msglines, (indent=2, msg=SubString("$key = $(vallines[1])")))
             else
diff --git a/base/pkgid.jl b/base/pkgid.jl
index 8c776d79a69cb..9878c0b0a8a40 100644
--- a/base/pkgid.jl
+++ b/base/pkgid.jl
@@ -32,7 +32,7 @@ function binpack(pkg::PkgId)
     uuid = pkg.uuid
     write(io, uuid === nothing ? UInt128(0) : UInt128(uuid))
     write(io, pkg.name)
-    return String(take!(io))
+    return unsafe_takestring!(io)
 end
 
 function binunpack(s::String)
diff --git a/base/show.jl b/base/show.jl
index 0a2976e7ebe42..d39fb687f5dd8 100644
--- a/base/show.jl
+++ b/base/show.jl
@@ -375,12 +375,12 @@ julia> io = IOBuffer();
 
 julia> printstyled(IOContext(io, :color => true), "string", color=:red)
 
-julia> String(take!(io))
+julia> takestring!(io)
 "\\e[31mstring\\e[39m"
 
 julia> printstyled(io, "string", color=:red)
 
-julia> String(take!(io))
+julia> takestring!(io)
 "string"
 ```
 
@@ -2609,7 +2609,7 @@ function show_tuple_as_call(out::IO, name::Symbol, sig::Type;
     end
     print_within_stacktrace(io, ")", bold=true)
     show_method_params(io, tv)
-    str = String(take!(buf))
+    str = takestring!(buf)
     str = type_limited_string_from_context(out, str)
     print(out, str)
     nothing
@@ -2718,7 +2718,7 @@ function type_depth_limit(str::String, n::Int; maxdepth = nothing)
         end
         prev = di
     end
-    return String(take!(output))
+    return unsafe_takestring!(output)
 end
 
 function print_type_bicolor(io, type; kwargs...)
@@ -3150,7 +3150,7 @@ summary(io::IO, x) = print(io, typeof(x))
 function summary(x)
     io = IOBuffer()
     summary(io, x)
-    String(take!(io))
+    takestring!(io)
 end
 
 ## `summary` for AbstractArrays
diff --git a/base/stat.jl b/base/stat.jl
index 506b5644dccbc..48967bbae0035 100644
--- a/base/stat.jl
+++ b/base/stat.jl
@@ -301,7 +301,7 @@ function filemode_string(mode)
         end
         complete && write(str, "-")
     end
-    return String(take!(str))
+    return unsafe_takestring!(str)
 end
 
 """
diff --git a/base/strings/annotated.jl b/base/strings/annotated.jl
index be4c6887d4a6d..5bb32abde2b9a 100644
--- a/base/strings/annotated.jl
+++ b/base/strings/annotated.jl
@@ -274,7 +274,7 @@ function annotatedstring(xs...)
             print(s, x)
         end
     end
-    str = String(take!(buf))
+    str = takestring!(buf)
     AnnotatedString(str, annotations)
 end
 
@@ -457,7 +457,7 @@ function annotated_chartransform(f::Function, str::AnnotatedString, state=nothin
         stop_offset  = last(offsets[findlast(<=(stop) ∘ first, offsets)::Int])
         push!(annots, ((start + start_offset):(stop + stop_offset), value))
     end
-    AnnotatedString(String(take!(outstr)), annots)
+    AnnotatedString(takestring!(outstr), annots)
 end
 
 ## AnnotatedIOBuffer
diff --git a/base/strings/basic.jl b/base/strings/basic.jl
index bf11199143c1e..927d86b79474a 100644
--- a/base/strings/basic.jl
+++ b/base/strings/basic.jl
@@ -681,7 +681,7 @@ function filter(f, s::AbstractString)
     for c in s
         f(c) && write(out, c)
     end
-    String(_unsafe_take!(out))
+    takestring!(out)
 end
 
 ## string first and last ##
diff --git a/base/strings/io.jl b/base/strings/io.jl
index acbd945c8e137..9b278122f5bc9 100644
--- a/base/strings/io.jl
+++ b/base/strings/io.jl
@@ -25,7 +25,7 @@ julia> io = IOBuffer();
 
 julia> print(io, "Hello", ' ', :World!)
 
-julia> String(take!(io))
+julia> takestring!(io)
 "Hello World!"
 ```
 """
@@ -68,7 +68,7 @@ julia> io = IOBuffer();
 
 julia> println(io, "Hello", ',', " world.")
 
-julia> String(take!(io))
+julia> takestring!(io)
 "Hello, world.\\n"
 ```
 """
@@ -113,7 +113,7 @@ function sprint(f::Function, args...; context=nothing, sizehint::Integer=0)
     else
         f(s, args...)
     end
-    String(_unsafe_take!(s))
+    takestring!(s)
 end
 
 function _str_sizehint(x)
@@ -147,7 +147,7 @@ function print_to_string(xs...)
     for x in xs
         print(s, x)
     end
-    String(_unsafe_take!(s))
+    takestring!(s)
 end
 
 function string_with_env(env, xs...)
@@ -164,7 +164,7 @@ function string_with_env(env, xs...)
     for x in xs
         print(env_io, x)
     end
-    String(_unsafe_take!(s))
+    takestring!(s)
 end
 
 """
@@ -298,10 +298,10 @@ Create a read-only `IOBuffer` on the data underlying the given string.
 ```jldoctest
 julia> io = IOBuffer("Haho");
 
-julia> String(take!(io))
+julia> takestring!(io)
 "Haho"
 
-julia> String(take!(io))
+julia> takestring!(io)
 "Haho"
 ```
 """
@@ -777,7 +777,7 @@ function unindent(str::AbstractString, indent::Int; tabwidth=8)
             print(buf, ' ')
         end
     end
-    String(take!(buf))
+    takestring!(buf)
 end
 
 function String(a::AbstractVector{Char})
diff --git a/base/strings/string.jl b/base/strings/string.jl
index 90d6e5b26ccd3..04ecdab089ce0 100644
--- a/base/strings/string.jl
+++ b/base/strings/string.jl
@@ -61,14 +61,9 @@ by [`take!`](@ref) on a writable [`IOBuffer`](@ref) and by calls to
 In other cases, `Vector{UInt8}` data may be copied, but `v` is truncated anyway
 to guarantee consistent behavior.
 """
-String(v::AbstractVector{UInt8}) = String(copyto!(StringMemory(length(v)), v))
-function String(v::Memory{UInt8})
-    len = length(v)
-    len == 0 && return ""
-    return ccall(:jl_genericmemory_to_string, Ref{String}, (Any, Int), v, len)
-end
+String(v::AbstractVector{UInt8}) = unsafe_takestring(copyto!(StringMemory(length(v)), v))
+
 function String(v::Vector{UInt8})
-    #return ccall(:jl_array_to_string, Ref{String}, (Any,), v)
     len = length(v)
     len == 0 && return ""
     ref = v.ref
@@ -83,6 +78,30 @@ function String(v::Vector{UInt8})
     return str
 end
 
+"""
+    takestring!(x) -> String
+
+Create a string from the content of `x`, emptying `x`.
+
+# Examples
+```jldoctest
+julia> v = [0x61, 0x62, 0x63];
+
+julia> s = takestring!(v)
+"abc"
+
+julia> isempty(v)
+true
+```
+"""
+takestring!(v::Vector{UInt8}) = String(v)
+
+"Create a string re-using the memory, if possible.
+Mutating the memory after calling this function is undefined behaviour."
+function unsafe_takestring(m::Memory{UInt8})
+    isempty(m) ? "" : ccall(:jl_genericmemory_to_string, Ref{String}, (Any, Int), m, length(m))
+end
+
 """
     unsafe_string(p::Ptr{UInt8}, [length::Integer])
 
diff --git a/base/strings/unicode.jl b/base/strings/unicode.jl
index ad047514c85a6..b2882b49d89b3 100644
--- a/base/strings/unicode.jl
+++ b/base/strings/unicode.jl
@@ -6,7 +6,7 @@ module Unicode
 import Base: show, ==, hash, string, Symbol, isless, length, eltype,
              convert, isvalid, ismalformed, isoverlong, iterate,
              AnnotatedString, AnnotatedChar, annotated_chartransform,
-             @assume_effects, annotations
+             @assume_effects, annotations, unsafe_takestring!
 
 # whether codepoints are valid Unicode scalar values, i.e. 0-0xd7ff, 0xe000-0x10ffff
 
@@ -689,7 +689,7 @@ function titlecase(s::AbstractString; wordsep::Function = !isletter, strict::Boo
         end
         c0 = c
     end
-    return String(take!(b))
+    return takestring!(b)
 end
 
 # TODO: improve performance characteristics, room for a ~10x improvement.
diff --git a/base/strings/util.jl b/base/strings/util.jl
index 0ba76e1c76fa0..2d530f5e2124f 100644
--- a/base/strings/util.jl
+++ b/base/strings/util.jl
@@ -1028,7 +1028,7 @@ function _replace_(str, pat_repl::NTuple{N, Pair}, count::Int) where N
         return String(str)
     end
     out = IOBuffer(sizehint=floor(Int, 1.2sizeof(str)))
-    return String(take!(_replace_finish(out, str, count, e1, patterns, replaces, rs)))
+    return takestring!(_replace_finish(out, str, count, e1, patterns, replaces, rs))
 end
 
 """
@@ -1214,7 +1214,7 @@ function bytes2hex(itr)
         b[2i - 1] = hex_chars[1 + x >> 4]
         b[2i    ] = hex_chars[1 + x & 0xf]
     end
-    return String(b)
+    return unsafe_takestring(b)
 end
 
 function bytes2hex(io::IO, itr)
@@ -1260,5 +1260,5 @@ function Base.rest(s::AbstractString, st...)
     for c in Iterators.rest(s, st...)
         print(io, c)
     end
-    return String(take!(io))
+    return takestring!(io)
 end
diff --git a/base/task.jl b/base/task.jl
index 6cb1ff785eeee..61cc103c70081 100644
--- a/base/task.jl
+++ b/base/task.jl
@@ -95,7 +95,7 @@ function show_task_exception(io::IO, t::Task; indent = true)
     else
         show_exception_stack(IOContext(b, io), stack)
     end
-    str = String(take!(b))
+    str = takestring!(b)
     if indent
         str = replace(str, "\n" => "\n    ")
     end
diff --git a/base/toml_parser.jl b/base/toml_parser.jl
index 4d07cfed05d8a..7dac4af022eca 100644
--- a/base/toml_parser.jl
+++ b/base/toml_parser.jl
@@ -315,7 +315,7 @@ function point_to_line(str::AbstractString, a::Int, b::Int, context)
         c == '\n' && break
         print(io1, c)
     end
-    return String(take!(io1.io)), String(take!(io2.io))
+    return takestring!(io1.io), takestring!(io2.io)
 end
 
 function Base.showerror(io::IO, err::ParserError)
diff --git a/base/util.jl b/base/util.jl
index 95d62c4a16e1d..e606e092ef959 100644
--- a/base/util.jl
+++ b/base/util.jl
@@ -77,7 +77,7 @@ function with_output_color(@nospecialize(f::Function), color::Union{Int, Symbol}
     iscolor = get(io, :color, false)::Bool
     try f(IOContext(buf, io), args...)
     finally
-        str = String(take!(buf))
+        str = takestring!(buf)
         if !iscolor
             print(io, str)
         else
@@ -109,7 +109,7 @@ function with_output_color(@nospecialize(f::Function), color::Union{Int, Symbol}
                 isempty(line) && continue
                 print(buf, enable_ansi, line, disable_ansi)
             end
-            print(io, String(take!(buf)))
+            print(io, takestring!(buf))
         end
     end
 end
diff --git a/base/uuid.jl b/base/uuid.jl
index 9b2da3c6409db..217c0b55adf7d 100644
--- a/base/uuid.jl
+++ b/base/uuid.jl
@@ -96,7 +96,7 @@ let groupings = [36:-1:25; 23:-1:20; 18:-1:15; 13:-1:10; 8:-1:1]
             u >>= 4
         end
         @inbounds a[24] = a[19] = a[14] = a[9] = '-'
-        return String(a)
+        return unsafe_takestring(a)
     end
 end
 
diff --git a/doc/src/base/strings.md b/doc/src/base/strings.md
index b7d16ffc7d487..b2ba92fc54981 100644
--- a/doc/src/base/strings.md
+++ b/doc/src/base/strings.md
@@ -34,6 +34,7 @@ Base.SubstitutionString
 Base.@s_str
 Base.@raw_str
 Base.@b_str
+Base.takestring!
 Base.Docs.@html_str
 Base.Docs.@text_str
 Base.isvalid(::Any)
diff --git a/doc/src/devdocs/functions.md b/doc/src/devdocs/functions.md
index 777afaa56348d..fb67dfd17c3e2 100644
--- a/doc/src/devdocs/functions.md
+++ b/doc/src/devdocs/functions.md
@@ -117,7 +117,7 @@ function lines(words)
             n += length(w)+1
         end
     end
-    String(take!(io))
+    takestring!(io)
 end
 import Markdown
 [string(n) for n in names(Core;all=true)
diff --git a/doc/src/manual/getting-started.md b/doc/src/manual/getting-started.md
index 2c69aabbda192..edec633245021 100644
--- a/doc/src/manual/getting-started.md
+++ b/doc/src/manual/getting-started.md
@@ -13,7 +13,7 @@ known as a read-eval-print loop or "REPL") by double-clicking the Julia executab
 using REPL
 io = IOBuffer()
 REPL.banner(io)
-banner = String(take!(io))
+banner = takestring!(io)
 import Markdown
 Markdown.parse("```\n\$ julia\n\n$(banner)\njulia> 1 + 2\n3\n\njulia> ans\n3\n```")
 ```
diff --git a/src/genericmemory.c b/src/genericmemory.c
index ea52fca66ba48..4a64b571ac367 100644
--- a/src/genericmemory.c
+++ b/src/genericmemory.c
@@ -193,7 +193,6 @@ JL_DLLEXPORT jl_value_t *jl_genericmemory_to_string(jl_genericmemory_t *m, size_
     }
     int how = jl_genericmemory_how(m);
     size_t mlength = m->length;
-    m->length = 0;
     if (how != 0) {
         jl_value_t *o = jl_genericmemory_data_owner_field(m);
         jl_genericmemory_data_owner_field(m) = NULL;
@@ -208,8 +207,6 @@ JL_DLLEXPORT jl_value_t *jl_genericmemory_to_string(jl_genericmemory_t *m, size_
         JL_GC_PUSH1(&o);
         jl_value_t *str = jl_pchar_to_string((const char*)m->ptr, len);
         JL_GC_POP();
-        if (how == 1) // TODO: we might like to early-call jl_gc_free_memory here instead actually, but hopefully `m` will die soon
-            jl_gc_count_freed(mlength);
         return str;
     }
     // n.b. how == 0 is always pool-allocated, so the freed bytes are computed from the pool not the object
diff --git a/stdlib/Base64/src/encode.jl b/stdlib/Base64/src/encode.jl
index 588b49aa28d97..d55421c52ff55 100644
--- a/stdlib/Base64/src/encode.jl
+++ b/stdlib/Base64/src/encode.jl
@@ -24,7 +24,7 @@ julia> write(iob64_encode, "Hello!")
 
 julia> close(iob64_encode);
 
-julia> str = String(take!(io))
+julia> str = takestring!(io)
 "SGVsbG8h"
 
 julia> String(base64decode(str))
@@ -211,6 +211,6 @@ function base64encode(f::Function, args...; context=nothing)
         f(IOContext(b, context), args...)
     end
     close(b)
-    return String(take!(s))
+    return takestring!(s)
 end
 base64encode(args...; context=nothing) = base64encode(write, args...; context=context)
diff --git a/stdlib/FileWatching/src/FileWatching.jl b/stdlib/FileWatching/src/FileWatching.jl
index 0c987ad01c828..27fc7231bcd2a 100644
--- a/stdlib/FileWatching/src/FileWatching.jl
+++ b/stdlib/FileWatching/src/FileWatching.jl
@@ -25,7 +25,7 @@ import Base: @handle_as, wait, close, eventloop, notify_error, IOError,
     _sizeof_uv_poll, _sizeof_uv_fs_poll, _sizeof_uv_fs_event, _uv_hook_close, uv_error, _UVError,
     iolock_begin, iolock_end, associate_julia_struct, disassociate_julia_struct,
     preserve_handle, unpreserve_handle, isreadable, iswritable, isopen,
-    |, getproperty, propertynames
+    |, getproperty, propertynames, unsafe_takestring
 import Base.Filesystem.StatStruct
 if Sys.iswindows()
     import Base.WindowsRawSocket
diff --git a/stdlib/FileWatching/src/pidfile.jl b/stdlib/FileWatching/src/pidfile.jl
index 4c821a3d897e4..3a8b9430f4f68 100644
--- a/stdlib/FileWatching/src/pidfile.jl
+++ b/stdlib/FileWatching/src/pidfile.jl
@@ -5,7 +5,8 @@ export mkpidlock, trymkpidlock
 
 using Base:
     IOError, UV_EEXIST, UV_ESRCH,
-    Process
+    Process,
+    unsafe_takestring
 
 using Base.Filesystem:
     File, open, JL_O_CREAT, JL_O_RDWR, JL_O_RDONLY, JL_O_EXCL,
@@ -285,7 +286,7 @@ function _rand_filename(len::Int=4) # modified from Base.Libc
     for i = 1:len
         slug[i] = chars[(Libc.rand() % length(chars)) + 1]
     end
-    return String(slug)
+    return unsafe_takestring(slug)
 end
 
 function tryrmopenfile(path::String)
diff --git a/stdlib/InteractiveUtils/src/InteractiveUtils.jl b/stdlib/InteractiveUtils/src/InteractiveUtils.jl
index 835988ddf149f..e7d10266677c6 100644
--- a/stdlib/InteractiveUtils/src/InteractiveUtils.jl
+++ b/stdlib/InteractiveUtils/src/InteractiveUtils.jl
@@ -147,7 +147,7 @@ function versioninfo(io::IO=stdout; verbose::Bool=false)
     if verbose
         cpuio = IOBuffer() # print cpu_summary with correct alignment
         Sys.cpu_summary(cpuio)
-        for (i, line) in enumerate(split(chomp(String(take!(cpuio))), "\n"))
+        for (i, line) in enumerate(split(chomp(takestring!(cpuio)), "\n"))
             prefix = i == 1 ? "  CPU: " : "       "
             println(io, prefix, line)
         end
diff --git a/stdlib/LibGit2/src/utils.jl b/stdlib/LibGit2/src/utils.jl
index f62663a6ea4ca..a1edce7ab403a 100644
--- a/stdlib/LibGit2/src/utils.jl
+++ b/stdlib/LibGit2/src/utils.jl
@@ -162,7 +162,7 @@ function git_url(;
     end
     seekstart(io)
 
-    return String(take!(io))
+    return takestring!(io)
 end
 
 function credential_identifier(scheme::AbstractString, host::AbstractString)
diff --git a/stdlib/Markdown/src/Common/block.jl b/stdlib/Markdown/src/Common/block.jl
index 1b5cc1a752bcb..d68db483f999d 100644
--- a/stdlib/Markdown/src/Common/block.jl
+++ b/stdlib/Markdown/src/Common/block.jl
@@ -114,7 +114,7 @@ function indentcode(stream::IO, block::MD)
                 break
             end
         end
-        code = String(take!(buffer))
+        code = takestring!(buffer)
         !isempty(code) && (push!(block, Code(rstrip(code))); return true)
         return false
     end
@@ -178,7 +178,7 @@ function blockquote(stream::IO, block::MD)
         end
         empty && return false
 
-        md = String(take!(buffer))
+        md = takestring!(buffer)
         push!(block, BlockQuote(parse(md, flavor = config(block)).content))
         return true
     end
@@ -236,7 +236,7 @@ function admonition(stream::IO, block::MD)
             end
         end
         # Parse the nested block as markdown and create a new Admonition block.
-        nested = parse(String(take!(buffer)), flavor = config(block))
+        nested = parse(takestring!(buffer), flavor = config(block))
         push!(block, Admonition(category, title, nested.content))
         return true
     end
@@ -326,7 +326,7 @@ function list(stream::IO, block::MD)
         return true
     end
 end
-pushitem!(list, buffer) = push!(list.items, parse(String(take!(buffer))).content)
+pushitem!(list, buffer) = push!(list.items, parse(takestring!(buffer)).content)
 
 # ––––––––––––––
 # HorizontalRule
diff --git a/stdlib/Markdown/src/GitHub/GitHub.jl b/stdlib/Markdown/src/GitHub/GitHub.jl
index 61807d267511d..f53aaaa00e2aa 100644
--- a/stdlib/Markdown/src/GitHub/GitHub.jl
+++ b/stdlib/Markdown/src/GitHub/GitHub.jl
@@ -21,9 +21,9 @@ function fencedcode(stream::IO, block::MD)
             if startswith(stream, string(ch) ^ n)
                 if !startswith(stream, string(ch))
                     if flavor == "math"
-                        push!(block, LaTeX(String(take!(buffer)) |> chomp))
+                        push!(block, LaTeX(takestring!(buffer) |> chomp))
                     else
-                        push!(block, Code(flavor, String(take!(buffer)) |> chomp))
+                        push!(block, Code(flavor, takestring!(buffer) |> chomp))
                     end
                     return true
                 else
diff --git a/stdlib/Markdown/src/parse/parse.jl b/stdlib/Markdown/src/parse/parse.jl
index 389099b2984f6..371d52cfaf53f 100644
--- a/stdlib/Markdown/src/parse/parse.jl
+++ b/stdlib/Markdown/src/parse/parse.jl
@@ -65,7 +65,7 @@ function parseinline(stream::IO, md::MD, config::Config)
         char = peek(stream, Char)
         if haskey(config.inner, char) &&
                 (inner = parseinline(stream, md, config.inner[char])) !== nothing
-            c = String(take!(buffer))
+            c = takestring!(buffer)
             !isempty(c) && push!(content, c)
             buffer = IOBuffer()
             push!(content, inner)
@@ -73,7 +73,7 @@ function parseinline(stream::IO, md::MD, config::Config)
             write(buffer, read(stream, Char))
         end
     end
-    c = String(take!(buffer))
+    c = takestring!(buffer)
     !isempty(c) && push!(content, c)
     return content
 end
diff --git a/stdlib/Markdown/src/parse/util.jl b/stdlib/Markdown/src/parse/util.jl
index aabfcbb3ddc62..cd8158780bd6d 100644
--- a/stdlib/Markdown/src/parse/util.jl
+++ b/stdlib/Markdown/src/parse/util.jl
@@ -141,7 +141,7 @@ function readuntil(stream::IO, delimiter; newlines = false, match = nothing)
         while !eof(stream)
             if startswith(stream, delimiter)
                 if count == 0
-                    return String(take!(buffer))
+                    return takestring!(buffer)
                 else
                     count -= 1
                     write(buffer, delimiter)
@@ -187,7 +187,7 @@ function parse_inline_wrapper(stream::IO, delimiter::AbstractString; rep = false
             if !(char in whitespace || char == '\n' || char in delimiter) && startswith(stream, delimiter^n)
                 trailing = 0
                 while startswith(stream, delimiter); trailing += 1; end
-                trailing == 0 && return String(take!(buffer))
+                trailing == 0 && return takestring!(buffer)
                 write(buffer, delimiter ^ (n + trailing))
             end
         end
diff --git a/stdlib/REPL/src/LineEdit.jl b/stdlib/REPL/src/LineEdit.jl
index 5af03e0df9b6d..464fdab5a8337 100644
--- a/stdlib/REPL/src/LineEdit.jl
+++ b/stdlib/REPL/src/LineEdit.jl
@@ -166,7 +166,7 @@ region_active(s::PromptState) = s.region_active
 region_active(s::ModeState) = :off
 
 
-input_string(s::PromptState) = String(take!(copy(s.input_buffer)))
+input_string(s::PromptState) = takestring!(copy(s.input_buffer))
 
 input_string_newlines(s::PromptState) = count(c->(c == '\n'), input_string(s))
 function input_string_newlines_aftercursor(s::PromptState)
@@ -1443,7 +1443,7 @@ function edit_input(s, f = (filename, line, column) -> InteractiveUtils.edit(fil
     end
     buf = buffer(s)
     pos = position(buf)
-    str = String(take!(buf))
+    str = takestring!(buf)
     lines = readlines(IOBuffer(str); keep=true)
 
     # Compute line
@@ -1672,7 +1672,7 @@ function normalize_key(key::Union{String,SubString{String}})
             write(buf, c)
         end
     end
-    return String(take!(buf))
+    return takestring!(buf)
 end
 
 function normalize_keys(keymap::Union{Dict{Char,Any},AnyDict})
@@ -2012,7 +2012,7 @@ function history_set_backward(s::SearchState, backward::Bool)
     nothing
 end
 
-input_string(s::SearchState) = String(take!(copy(s.query_buffer)))
+input_string(s::SearchState) = takestring!(copy(s.query_buffer))
 
 function reset_state(s::SearchState)
     if s.query_buffer.size != 0
@@ -2100,7 +2100,7 @@ function refresh_multi_line(termbuf::TerminalBuffer, terminal::UnixTerminal,
     return ias
 end
 
-input_string(s::PrefixSearchState) = String(take!(copy(s.response_buffer)))
+input_string(s::PrefixSearchState) = takestring!(copy(s.response_buffer))
 
 write_prompt(terminal, s::PrefixSearchState, color::Bool) = write_prompt(terminal, s.histprompt.parent_prompt, color)
 prompt_string(s::PrefixSearchState) = prompt_string(s.histprompt.parent_prompt.prompt)
diff --git a/stdlib/REPL/src/REPL.jl b/stdlib/REPL/src/REPL.jl
index ddf2f55d0b9f7..7e84b83509041 100644
--- a/stdlib/REPL/src/REPL.jl
+++ b/stdlib/REPL/src/REPL.jl
@@ -880,7 +880,7 @@ function hist_from_file(hp::REPLHistoryProvider, path::String)
 end
 
 function add_history(hist::REPLHistoryProvider, s::PromptState)
-    str = rstrip(String(take!(copy(s.input_buffer))))
+    str = rstrip(takestring!(copy(s.input_buffer)))
     isempty(strip(str)) && return
     mode = mode_idx(hist, LineEdit.mode(s))
     !isempty(hist.history) &&
@@ -1007,7 +1007,7 @@ function history_move_prefix(s::LineEdit.PrefixSearchState,
                              prefix::AbstractString,
                              backwards::Bool,
                              cur_idx::Int = hist.cur_idx)
-    cur_response = String(take!(copy(LineEdit.buffer(s))))
+    cur_response = takestring!(copy(LineEdit.buffer(s)))
     # when searching forward, start at last_idx
     if !backwards && hist.last_idx > 0
         cur_idx = hist.last_idx
@@ -1049,7 +1049,7 @@ function history_search(hist::REPLHistoryProvider, query_buffer::IOBuffer, respo
     qpos = position(query_buffer)
     qpos > 0 || return true
     searchdata = beforecursor(query_buffer)
-    response_str = String(take!(copy(response_buffer)))
+    response_str = takestring!(copy(response_buffer))
 
     # Alright, first try to see if the current match still works
     a = position(response_buffer) + 1 # position is zero-indexed
@@ -1106,7 +1106,7 @@ end
 LineEdit.reset_state(hist::REPLHistoryProvider) = history_reset_state(hist)
 
 function return_callback(s)
-    ast = Base.parse_input_line(String(take!(copy(LineEdit.buffer(s)))), depwarn=false)
+    ast = Base.parse_input_line(takestring!(copy(LineEdit.buffer(s))), depwarn=false)
     return !(isa(ast, Expr) && ast.head === :incomplete)
 end
 
@@ -1668,7 +1668,7 @@ let matchend = Dict("\"" => r"\"", "\"\"\"" => r"\"\"\"", "'" => r"'",
             pos = nextind(code, last(j))
         end
         print(buf, SubString(code, pos, lastindex(code)))
-        return String(take!(buf))
+        return takestring!(buf)
     end
 end
 
diff --git a/test/iobuffer.jl b/test/iobuffer.jl
index b5b34a2dbed8c..843cc72b6b5a8 100644
--- a/test/iobuffer.jl
+++ b/test/iobuffer.jl
@@ -54,6 +54,26 @@ bufcontents(io::Base.GenericIOBuffer) = unsafe_string(pointer(io.data), io.size)
     @test_throws ArgumentError seek(io, 0)
 end
 
+@testset "takestring!" begin
+    buf = IOBuffer()
+    write(buf, "abcø")
+    s = takestring!(buf)
+    @test isempty(takestring!(buf))
+    @test s == "abcø"
+    write(buf, "xyz")
+    @test takestring!(buf) == "xyz"
+    buf = IOBuffer()
+
+    # Test with a nonzero offset in the buffer
+    v = rand(UInt8, 8)
+    for i in 1:8
+        pushfirst!(v, rand(UInt8))
+    end
+    buf = IOBuffer(v)
+    s = String(copy(v))
+    @test takestring!(buf) == s
+end
+
 @testset "Read/write readonly IOBuffer" begin
     io = IOBuffer("hamster\nguinea pig\nturtle")
     @test position(io) == 0
diff --git a/test/strings/basic.jl b/test/strings/basic.jl
index 874607f3c1b20..f081d87a32d3e 100644
--- a/test/strings/basic.jl
+++ b/test/strings/basic.jl
@@ -49,6 +49,24 @@ using Random
     end
 end
 
+@testset "takestring!" begin
+    v = [0x61, 0x62, 0x63]
+    old_mem = v.ref.mem
+    @test takestring!(v) == "abc"
+    @test isempty(v)
+    @test v.ref.mem !== old_mem # memory is changed
+    for v in [
+        UInt8[],
+        [0x01, 0x02, 0x03],
+        collect(codeunits("æøå"))
+    ]
+        cp = copy(v)
+        s = takestring!(v)
+        @test isempty(v)
+        @test codeunits(s) == cp
+    end
+end
+
 @testset "{starts,ends}with" begin
     @test startswith("abcd", 'a')
     @test startswith('a')("abcd")