Shell Programming and Scripting

HI Team,

I have script to find the invalid character in file.

Code:

f=’pallvi\mahajan’
                 n=0
 while (( $n <= ${#f} ));
 do
 c="${f:$n:1}"
 echo '$c'
 if [[ "$c" = *[^[:space:]*] ]];
 then 
 grep -sq $c valid.txt
 if  [ $? -eq  1 ];
 then
 echo "$f" >> f.txt
 break
 fi
 fi
 n=$((n+1))
 done

My valid.txt file is

Code:

a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E  F G H I J K L M N O P Q R S T U V W X Y Z ( ) { }  \t 1 2 3 4 5 6 7 8 9 0 - / :  ? + \n . , '

But my script is not searching \ character which is string f='pallvi\mahajan'
Please let me know how i can do this.

I have run this script in debugging mode and it is running but this variable is not putting in file f.txt
while running script in debussgibg mode, i checked grep -sq is giving error when searching \
exit status is 2 in that time.

Your script is wrong in many ways.

Code:

f=’pallvi\mahajan’

This attempts to run the command pallvi\mahajan and stores its output, if any, in f. Since no such command exists, you get nothing. I believe you meant:

Code:

f='pallvi\mahajan'

Also, variables don't expand in single quotes. echo '$c' will print the literal text $c. I believe you meant echo "$c"

Also, some characters have a special meaning to grep. \ for example. To make grep take all characters you give it literally, tell it -F.

Also, you don't need to use $? to fit grep into an expression. Just use if ! grep ... then ...

Also, if you know your shell has [[ string == *str* ]], you could use it instead of grep. Or you could replace valid.txt and most of this program with one case, really.

The #1 mistake is the grep.
1. quote "$c"
2. a single \ is an RE error, must be \\
Because one can prepend a \ to a normal character, you can do

Code:

grep -sq \\"$c" valid.txt

\\ is necessary for the shell; it will pass a single \ to grep.
You better use a non-RE grep

Code:

fgrep -sq "$c" valid.txt

thanks but this did not work for another character getting backrefrence error

Code:

grep -sq \9 valid.txt

while running script in debug mode, i found this error and also this are passing another character also backslash

Ah, even \9 is a special meaning in an RE. Not to speak of special characters.
Then take my 2nd suggestion, a non-RE grep!

This also not work fgrep

can you suggest me something

---------- Post updated at 03:49 PM ---------- Previous update was at 03:37 PM ----------

while runnig in script in debug mode, i find this using fgrep.

Code:

  echo '$c'
 $c
 + [[ \ = *[^[:space:]*] ]]
 + grep -sq '\' valid.txt
 last character is \
 + '[' 2 -eq 1 ']'
 + n=7
 + ((  7 <= 14  ))
 + c=m
 + echo '$c'