How can I extract the first two characters of a string in shell scripting?

You can use printf:

$ original='USCAGoleta9311734.5021-120.1287855805'
$ printf '%-.2s' "$original"
US

Just for the sake of fun Ill add a few that, although they are over complicated and useless, they were not mentioned :

head -c 2 <( echo 'USCAGoleta9311734.5021-120.1287855805')

echo 'USCAGoleta9311734.5021-120.1287855805' | dd bs=2 count=1 status=none

sed -e 's/^\(.\{2\}\).*/\1/;' <( echo 'USCAGoleta9311734.5021-120.1287855805')

cut -c 1-2 <( echo 'USCAGoleta9311734.5021-120.1287855805')

python -c "print(r'USCAGoleta9311734.5021-120.1287855805'[0:2])"

ruby -e 'puts "USCAGoleta9311734.5021-120.1287855805"[0..1]'

How to consider Unicode + UTF-8

Let's do a quick test for those interested in Unicode characters rather than just bytes. Each character of áéíóú (acute accented vowels) is made up of two bytes in UTF-8. With:

printf 'áéíóú' | LC_CTYPE=en_US.UTF-8 awk '{print substr($0,1,3);exit}'
printf 'áéíóú' | LC_CTYPE=C awk '{print substr($0,1,3);exit}'
printf 'áéíóú' | LC_CTYPE=en_US.UTF-8 head -c3
echo
printf 'áéíóú' | LC_CTYPE=C head -c3

we get:

áéí
á
á
á

so we see that only awk + LC_CTYPE=en_US.UTF-8 considered the UTF-8 characters. The other approaches took only three bytes. We can confirm that with:

printf 'áéíóú' | LC_CTYPE=C head -c3 | hd

which gives:

00000000  c3 a1 c3                                          |...|
00000003

and the c3 by itself is trash, and does not show up on the terminal, so we saw only á.

awk + LC_CTYPE=en_US.UTF-8 actually returns 6 bytes however.

We could also have equivalently tested with:

printf '\xc3\xa1\xc3\xa9\xc3\xad\xc3\xb3\xc3\xba' | LC_CTYPE=en_US.UTF-8 awk '{print substr($0,1,3);exit}'

and if you want a general parameter:

n=3
printf 'áéíóú' | LC_CTYPE=en_US.UTF-8 awk "{print substr(\$0,1,$n);exit}"

Question more specific about Unicode + UTF-8: https://superuser.com/questions/450303/unix-tool-to-output-first-n-characters-in-an-utf-8-encoded-file

Related: https://unix.stackexchange.com/questions/3454/grabbing-the-first-x-characters-for-a-string-from-a-pipe

Tested on Ubuntu 21.04.