Easiest way to capitalize a string within bash 3.2?

Question

For example: var=dog and echo $var output is dog. Capitalize $var expected output Dog.

Tried multiple ways but just not getting the expected output. Some attempts:

echo $var | sed "s/[a-z]\&[:upper:]//"  #dog
echo $var | sed "s/([a-z])/[:upper:]/"  #dog

Answer 1

tl;dr:

• macOS, with Unicode support, OR cross-platform, but ASCII-only, and for background information:

  • See the tr solution below.

• GNU utilities, with Unicode support (Linux: preinstalled; macOS: installable via Homebrew):

  • sed 's/^./\u&/' <<<'dog' # -> 'Dog'
    • macOS: after installing with brew install gnu-sed, use gsed instead of sed
  • awk alternative: see dev-null's answer
    • macOS: after installing with brew install gawk, use gawk instead of awk.

• Cross-platform, with Unicode support:

  • perl: see dawg's answer
  • python: see idjaw's answer

• Bash 4+, with Unicode support, which on macOS you can also install with Homebrew:

  • echo "${var^}"

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Try

var='dog'
echo "$(tr '[:lower:]' '[:upper:]' <<<"${var:0:1}")${var:1}" # -> 'Dog'

• tr '[:lower:]' '[:upper:]' <<<"${var:0:1}" extracts the 1st char from $var (${var:0:1}) and uses tr to translate it to uppercase.

• ${var:1} returns everything from the 2nd char in $var's value.

Note that this solution is Unicode-aware^[1], unlike the macOS awk and Python 2.x solutions ^{Update: @idjaw fixed the Python 2.x solution with .decode('utf-8')}, and presumably also slightly faster than them (tr is lighter-weight than awk and python).

^{[1] This applies to the BSD tr version that comes with macOS. GNU tr, by contrast, does not handle non-ASCII characters correctly - as John1024 notes, according to Wikipedia, "Most versions of tr, including GNU tr and classic Unix tr, operate on single-byte characters and are not Unicode compliant.".}

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As for your attempt at a sed solution:

Using macOS's (BSD) sed, I'm not aware of any substring-manipulation features.

If you had GNU sed - which you could install via Homebrew - you could use the following:

sed 's/^./\u&/' <<<'dog' # -> 'Dog'

\u tells GNU Sed to capitalize the following letter. Sadly, you can't do that with macOS's Sed.

[:upper:] only ever works as a matching character class, it never performs transformation, which is why your command didn't work.
The only exception is tr, where you can pair an [:upper:] with a [:lower:] to effect transformation, as in my solution above.

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Sneak preview of a Bash 4+ solution:

var='dog'; echo "${var^}"