The answers using awk fail if the number of matches is too large (which happens to be my situation). For the answer from loki-astariloki-astari, the following error is reported:
awk -F" '{print NF-1}' foo.txt
awk: program limit exceeded: maximum number of fields size=32767
FILENAME="foo.txt" FNR=1 NR=1
For the answer from enzotibenzotib (and the equivalent from manatworkmanatwork), a segmentation fault occurs:
awk '{ gsub("[^\"]", ""); print length }' foo.txt
Segmentation fault
The sed solution by maxschlepzigmaxschlepzig works correctly, but is slow (timings below).
Some solutions not yet suggested here. First, using grep:
grep -o \" foo.txt | wc -w
And using perl:
perl -ne '$x+=s/\"//g; END {print "$x\n"}' foo.txt
Here are some timings for a few of the solutions (ordered slowest to fastest); I limited things to one-liners here. 'foo.txt' is a file with one line and one long string which contains 84922 matches.
## sed solution by [maxschlepzig]
$ time sed 's/[^"]//g' foo.txt | awk '{ print length }'
84922
real 0m1.207s
user 0m1.192s
sys 0m0.008s
## using grep
$ time grep -o \" foo.txt | wc -w
84922
real 0m0.109s
user 0m0.100s
sys 0m0.012s
## using perl
$ time perl -ne '$x+=s/\"//g; END {print "$x\n"}' foo.txt
84922
real 0m0.034s
user 0m0.028s
sys 0m0.004s
## the winner: updated tr solution by [maxschlepzig]
$ time tr -d -c '\"\n' < foo.txt | awk '{ print length }'
84922
real 0m0.016s
user 0m0.012s
sys 0m0.004s
