Search for a part of a string in a file in shell - shell

Question

I have a file with a list of names in it. I am trying to search for names with a certain group of strings and print them to a new file in shell. Can you please help?
Here's what I am looking at.
Text file(names.txt) contains names like
New York_USA
Delhi
Moscow
Tokyo
Austin_USA
Beijing
Chicago_USA
I am trying to get the names with _USA in a seperate file.
Here's what I have tried
#/bin/ksh
for city in "cat names.txt"
do
if ["$city" =~ "*_USA"]
then
echo "$city in USA" > USAnames.txt
fi
done

Answer 1

You just need to execute the cat command instead of quoting it, fix your test operator ([ --> [[), and append >> instead of overwrite >, and write a regex instead of a glob pattern:
#/bin/ksh
for city in `cat names.txt` # notice the back quotes
do
if [[ "$city" =~ .*_USA ]]
then
echo "$city in USA" >> USAnames.txt
fi
done
A more idiomatic way would perhaps be:
#/bin/ksh
while read city
do
if [[ "$city" =~ .*_USA ]]
then
echo "$city in USA" >> USAnames.txt
fi
done < names.txt

Answer 2

Simply use grep :
grep '_USA$' your_file> new_file

Answer 3

Use awk or sed will be easier
if you want the output to be like this
New York_USA in USA
Austin_USA in USA
Chicago_USA in USA
use
awk '/_USA$/ {print $0, "in USA"}' names.txt > USAnames.txt
or sed
sed -n 's/\(.*\)_USA$/\0 in USA/p' names.txt > USAnames.txt
or if you want output to be
New York in USA
Austin in USA
Chicago in USA
use
awk -F_ '/_USA$/ {print $1,"in USA"}' names.txt > USAnames.txt
or sed
sed -n 's/\(.*\)_USA$/\1 in USA/p' names.txt > USAnames.txt
Edit
you can also use perl to print out the USA cities
#!/usr/bin/env perl
open(NAMES, "names.txt");
while (<NAMES>) {
chomp;
print "$_ in USA\n" if /_USA$/; # Chicago_USA in USA
# print "$1 in USA\n" if /(.*)_USA$/; # Chicago in USA
}
close(NAMES);