Searching a string for a character

turbulence · #1 (**permalink**) 11-29-2004

I have a co-worker that is trying to make a Wheel of Fortune game and he wants to know if there is a way to search a string for the letter given by the user.

zazzybob · #2 (**permalink**) 11-29-2004

Code:

echo "string" | grep 'x' >/dev/null 2>&1
if [ "$?" -eq "0" ]; then
  echo "Found x in string"
else
  echo "Couldnt find it"
fi

You get the idea....

Check out my hangman shell script - you can see the technique employed.

I wish I had a job like your co-worker!

Cheers
ZB

turbulence · #3 (**permalink**) 11-29-2004

Thanks for the help.

manthasirisha · #4 (**permalink**) 01-10-2006

Zazzybob,

I had the same probelm as turbulence's co-worker...and ur solution really worked.. but can u please explain the idea behind ur solution?
i didnt get what is the significance of /dev/null there in the code?

thanks
sirisha

vino · #5 (**permalink**) 01-10-2006

Quote:

Originally Posted by manthasirisha

i didnt get what is the significance of /dev/null there in the code?

Grep, in its simplest form, has this habit of shouting out loud, about the things it discovered. And if it did find, then the exit status is 0. Else 1.

In the OP's case, he wants only detect the presence of a letter in a string. So whatever grep outputs, be it success or failure, discard it.

Here is a non-grep solution as well

Code:

[~/temp]$ echo $LANG
en_US.UTF-8
[~/temp]$ [[ "$LANG" == *US* ]] && echo "US LANG" || echo "LOCALE"
US LANG
[~/temp]$

manthasirisha · #6 (**permalink**) 01-11-2006

vino,

i am afraid if i understand what u suggested. Your explantion of how grep works and thereby comparing the exit status of grep to detect the presence of a letter in the string is understood, but i didnt quite follow two aspects:

1. why is there a /dev/null in his piece of code?
2. How are achieving the same without a grep in your solution?

can you please take efforts to elaborate?

Thanks a ton again,
Sirisha

vino · #7 (**permalink**) 01-11-2006

Quote:

Originally Posted by manthasirisha

1. why is there a /dev/null in his piece of code?

I did mention that if grep finds anything, it will output whatever it found. Together with that, the exit status will be set accordingly.

See this

Code:

[/tmp]$ cat xyz
maroon
pink
yellow
[/tmp]$ grep pink xyz
pink
[/tmp]$ echo $?
0
[/tmp]$ grep pink xyz 1> /dev/null
[/tmp]$ echo $?
0
[/tmp]$ grep pink xyz.file 1> /dev/null
grep: xyz.file: No such file or directory
[/tmp]$ echo $?
2
[/tmp]$ grep pink xyz.file 1> /dev/null 2> /dev/null
[/tmp]$ echo $?
2
[/tmp]$ grep pink xyz 1> /dev/null 2> /dev/null
[/tmp]$ echo $?
0
[/tmp]$

That should explain the role of /dev/null. If not, read it from up the wiki site.

Quote:

Originally Posted by manthasirisha

2. How are achieving the same without a grep in your solution?

The non-grep solution makes use of a shell-builtin.

See this thread - String extraction from user input - sh

vino

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