I searched SO and found that to uppercase a string following would work

str="Some string"
echo ${str^^}

But I tried to do a similar thing on a command-line argument, which gave me the following error


             ## Output
echo ${1^^}  ## line 3: ${1^^}: bad substitution
echo {$1^^}  ## No error, but output was still smaller case i.e. no effect

How could we do this?


The syntax str^^ which you are trying is available from Bash 4.0 and above. Perhaps yours is an older version (or you ran the script with sh explicitly):

Try this:

str="Some string"
printf '%s\n' "$str" | awk '{ print toupper($0) }'
  • 1
    From mtk's words I understood that case modification actually works for him with variables.
    – manatwork
    Oct 16 '12 at 12:46
  • 1
    @manatwork That is not clearly stated in the initial question. The bad substitution error message is the same as you would get with older bash versions.
    – Bernhard
    Oct 16 '12 at 12:48
  • 4
    You are correct. I checked the version, its 3.2.25. Your solution works and also I tried tr '[a-z]' [[A-Z]'.
    – mtk
    Oct 16 '12 at 12:51
  • 26
    @mtk That should be tr '[a-z]' '[A-Z]'.
    – l0b0
    Oct 17 '12 at 9:43
  • 3
    I'm running GNU bash, version 4.3.42(1)-release (x86_64-apple-darwin14.5.0), and I get the same error as OP, so I don't think this is available on any bash 4.0 and above as you say. Jan 26 '16 at 23:19
echo "lowercase" | tr a-z A-Z


  • 3
    I think POSIX does not require the / as in tr /a-z/ /A-Z/ before my edit: this just works because it replaces / by / but is useless: pubs.opengroup.org/onlinepubs/9699919799/utilities/tr.html There also exists the more obscure and less useful tr '[:lower:]' '[:upper:]'. May 9 '18 at 16:22
  • Correct. tr is very different, but it works.
    – Doug
    Sep 6 '18 at 16:52
  • umlauts are not working with this.
    – Ievgen
    Jan 31 '19 at 15:04
  • 1
    As @CiroSantilli冠状病毒审查六四事件法轮功 mentioned, you can use `tr '[:lower:]' '[:upper:]' to handle non-a-z characters. (Indeed, the "less useful" comment seems to be the opposite. using lower/upper covers a wider range of characters.)
    – jasonkarns
    Apr 8 '20 at 13:30

Be careful with tr unless A-Z is all you use. For other locales even '[:lower:]' '[:upper:]' fails, only awk's toupper and bash (v4+) works

$ str="abcåäö"
$ echo "$str"|tr '/a-z/' '/A-Z/'
$ echo "$str"|LC_ALL=sv_SE tr '[:lower:]' '[:upper:]'
$ echo "$str"|awk '{print toupper($0)}'
$ echo ${str^^} # Bash 4.0 and later
$ echo ${STR,,}
  • 1
    FWIW, tr '[:lower:]' '[:upper:]' is working now for your example on OS X at least (also with LC_ALL=sv_SE)
    – Ethan
    Mar 31 '17 at 21:57

Alternatively, you could switch to ksh or zsh which have had case conversion support for decades (long before bash's ${var^^} added in 4.0), though with a different syntax:

#! /bin/ksh -
typeset -u upper="$1"
printf '%s\n' "$upper"

(also works with zsh; note that in pdksh/mksh, that only works for ASCII letters).

With zsh, you can also use the U parameter expansion flag:

#! /bin/zsh -
printf '%s\n' "${(U)1}"

POSIXLY, you can use:

awk 'BEGIN{print toupper(ARGV[1])}' "$1"

There's also:

printf '%s\n' "$1" | tr '[:lower:]' '[:upper:]'

But in a few implementations, including GNU tr, that only works for single-byte characters (so in UTF-8 locales, only on ASCII letters).


If someone is still getting error trying ${str^^}, you can try python -c or perl It is likely because bash version is lower than 4.

But, so far bash 4 or over is working swiftly with the existing solution.

L2U="I will be upper"

Using python -c in bash

python -c "print('$L2U'.upper())"

Similarly it also can be used to capitalise with:

service="bootup.sh on home"
python -c "print('$service'.capitalize())"
Bootup.sh on home

Using perl

echo $L2U | perl -ne 'print "\U$_"'

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