Shell Programming and Scripting

while read line
do 
              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
done < client.txt

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 . , '

#!/bin/bash
valid=( $'\t' $'\n' \\ \( \) \{ \} \' - / : ? + . , {a..z} {A..Z} {0..9} )
v="${valid[@]}"

while read line
do
    for((n=0;n<${#line};n++))
    do
       c=${line:$n:1}
       [[ "$c" = '\' || "$c" = '?' ]] && c=\\"$c"

       if [[ "${v/$c/}" = "${valid[@]}" ]]
       then
          echo "Invalid character: ${line:$n:1} found in $line"
       else
          echo "$c" >> f.txt
       fi
    done
done < client.txt

#!/bin/bash
valid=( $'\t' $'\n' \\ \( \) \{ \} \' - / : ? + . , {a..z} {A..Z} {0..9} )
v="${valid[@]}"

while read line
do
    for((n=0;n<${#line};n++))
    do
       c=${line:$n:1}
       [[ "$c" = '\' || "$c" = '?' ]] && c=\\"$c"

       if [[ "${v/$c/}" = "${valid[@]}" ]]
       then
          echo "Invalid character: ${line:$n:1} found in $line" >> f.txt
       fi
    done
done < client.txt

cat client.txt
pallvi mahajan
lonodn #enterprise
kite \ pallvi
sunny sapen20\45\65

Invalid character: # found in lonodn #enterprise

valid=( $'\t' $'\n' \\ \( \) \{ \} \' - / : ? + . , {a..z} {A..Z} {0..9} )

valid=( $'\t' $'\n' \( \) \{ \} \' - / : ? + . , {a..z} {A..Z} {0..9} )

while read -r line

[[ "$c" = '\' || "$c" = '?' ]] && c=\\"$c" 
        if [[ "${v/$c/}" = "${valid[@]}" ]]

[[ "$c" = '\' || "$c" = '?' ]] && c=\\"$c"

if [[ "${v/$c/}" = "${valid[@]}" ]]