deleting the part of the file(overwrite) using start and end point

Shell Programming and Scripting
21

no in actual code am setting flag in some "if" conditon which is inside this grep-while loop... when this while loop ends i am utilizing the set flag to do some operations but flag is reset to 0 when this grep-while loop ends... what to do ??

22

What is the if condition? may be we can work that out, that might be easy...

--ahamed

23

okay wait.. let me paste the partial code here...

flag=0
while read linexT
do
                                                 len=${#linexT}
                                                 charlast=${linexT:$len-1:$len}
                                                charfirst=${linexT:0:1}
                                                 if [ "$charlast" = "," ]
                                                 then
                                                      line11=${linexT:0:$len-1}
                                                 else
                                                      line11=$linexT
                                                 fi
                                                 if [ "$charfirst" = ">" ]
                                                 then
                                                           
#                                               here somewhere inbetween i am checking whether 
if flag=0
then
                do someting here
fi
fi
 
                   if [[ "$charfirst" = "<" ]]
                                                 then
                                                         line11=${line11:2:$len}
                                                        echo "missing in second: $line11"
                                                        colname1=$( echo $line11 | awk -F\` '{print $2}' )
                                                       line333=`cat tablextract2.sql | grep -w -i $colname1`
                                                        grep -w -i $colname1 tablextract2.sql | while read line22 ; do
 if [[ `expr match "$line11" ".*PRIMARY KEY.*"` = "0" ]]  &&  [[ `expr match "$line22" ".*PRIMARY KEY.*"` = "0" ]] && [[ "$key1" != "KEY" ]] &&  [[ "$key2" != "KEY" ]] && [[ `expr match "$line11" ".*UNIQUE KEY.*"` = "0" ]]  &&  [[ `expr match "$line22" ".*UNIQUE KEY.*"` = "0" ]]
         then
                                if grep -i -q "auto_increment" <<<$line22
                                then
                                         insert_column "$table_name1" "PRIMARY KEY (\`$colname1\`)"
                                         modify "$table_name1" "$line22"
                                        flag=1
                                        echo "flag: $flag"
                                else
                                         modify "$table_name1" "$line22"
                                fi
fi
done
 
done < tmp.sql

---------- Post updated at 02:18 PM ---------- Previous update was at 02:14 PM ----------

and also how to close a duplicate thread...?

24

One way is to make use of tmp files...

grep -w -i $colname1 tablextract2.sql > /tmp/tmp.$$
while read line; do
  echo "$line"
  flag=1
  echo "flag: $flag"
done < /tmp/tmp.$$
 
echo "flag: $flag"
 
rm -f /tmp/tmp.$$

--ahamed

1 Like
25

oh this will work i guess.. thanks :-)... but what is tmp.$$...?

26

$$ is the process ID of the shell - often used to make (somewhat) unique filenames.

1 Like
27

oh okay got it :slight_smile: thanks

28

This is not an issue with bash. Once you understand that the pipe launches a subshell, it comes as obvious that the parent shell does not know what the subshell did to its variable.

1 Like
29

oh does it mean like a sub thread in main thread.... or the scope of the variable dude to different shells..?

30

The behaviour is not same in ksh.

#!/bin/ksh
var=123;
echo $var
echo $var | while read line
do
  var=456
  echo $var
done
echo $var
 
[root@bt]./run
123
456
456

#!/bin/bash
var=123;
echo $var
echo $var | while read line
do
  var=456
  echo $var
done
echo $var
 
[root@bt]./run
123
456
123

--ahamed

2 Likes
31

Thanks everyone.. i finally completed the code.. :slight_smile: woudlnt have done without the help from all you guys.. thanks again :slight_smile: