How to check for a matching pattern in bash?

Question

I have a file in which value starts with ABC or ABD.

After fetching the value from input file how to check it starts with ABC or ABD?

eg:

value=$(cat file | awk 'NF{print;exit}' | awk '{print $1}')

and now I want to check this $value is starting with ABC or ABD . how?

No. value=$(cat file | awk 'NF{print;exit}' | awk '{print $1}') and now I want to check this $value is starting with ABC or ABD — Anony, Jan 12 '18 at 03:44
Why check it in bash? why not check it in awk, since you're already using that? — steeldriver, Jan 12 '18 at 03:52
There are several ways to do anything. grep is often used for pattern matching. see man grep Related:https://askubuntu.com/questions/587264/how-to-find-lines-matching-a-pattern-and-delete-them — Elder Geek, Jan 12 '18 at 04:13
FYI there's no need to use cat, and there's no need to use awk twice: your command can be reduced to awk 'NF {print $1; exit}' file — steeldriver, Jan 12 '18 at 04:20
I have to fetch value from a file that s why cat. Yea, awk oen is true..Thank you.. — Anony, Jan 12 '18 at 04:32

John1024 · Answer 1 · 2018-01-12T04:48:18.823

To check if a shell variable starts with ABC or ABD, a traditional (and very portable) method is to use a case statement:

case "$value" in
  AB[CD]*) echo yes;;
   *)      echo no;;
esac

Because this requires no external processes, it should be fast.

Alternatively, one can use a test command:

if [ "${value#AB[CD]}" != "$value" ]
then
   echo yes
else
   echo no
fi

This is also quite portable.

Lastly, one can use the more modern and less portable test command:

if [[ $value == AB[CD]* ]]
then
   echo yes
else
   echo no
fi

To read the first nonempty line of a file and test if its first field start with ABC or ABD:

awk 'NF{if ($1~/^AB[CD]/) print "yes"; else print "no";exit}' file

Jay · Answer 2 · 2018-01-12T05:38:14.713

2

Try this:

 echo $value | grep -c "^AB[CD]"

This will return 1 if the pattern is present at the beginning.

edited Jan 12 '18 at 05:38

answered Jan 12 '18 at 03:59

Jay

2 Answers2