How to find substring inside a string or how to grep a variable

Question

I m using BASH  and I don t know how to find a substring  It keeps failing  I ve got a string  should this be an array    Below  LIST is a string list of database names  SOURCE is the reply  one of those databases  The following still doesn t work   echo                                                                      echo                     DB2 Offline Backup Script                        echo                                                                      echo  What s the name of of the  database you would like to backup   echo  It will be named one in this list   echo    LIST  db2 list database directory   grep  Database alias    awk   print  4    echo  LIST echo    echo                                                                      echo -n   gt  gt  gt    read -e SOURCE  if expr match   LIST    SOURCE   then     echo  match      exit -1 else     echo  no match  fi exit -1   I ve also tried this but doesn t work   if    expr match   LIST    SOURCE      then

User · Answer

This works in Bash without forking external commands:

function has_substring() {
   [[ "$1" != "${2/$1/}" ]]
}

Example usage:

name="hello/world"
if has_substring "$name" "/"
then
   echo "Indeed, $name contains a slash!"
fi

User · Answer

If you re using bash you can just say  if grep -q   SOURCE   lt  lt  lt    LIST    then         fi

User · Answer

expr match   LIST    SOURCE    don t work because of this function search   SOURCE from begin of the string and return the position just after pattern  SOURCE if found else 0  So you must write another code   expr match   LIST        SOURCE  or expr   LIST          SOURCE    The expression  SOURCE must be double quoted so as a parser may set substitution  Single quoted not substitute and the code above will search textual string  SOURCE from the beginning of the  LIST  If you need the beginning of the string subtract the length  SOURCE e g    SOURCE   You may write also  expr   LIST          SOURCE      This function just extract  SOURCE from   LIST and return it  You ll get empty string else  But they problem with double double quote  I don t know how it resolve without using additional variable  It s light solution  So you may write in C  There is ready function strstr  Don t use expr index   So is very attractive  But index search not substring and only first char

User · Answer

LIST  some string with a substring you want to match  SOURCE  substring  if echo   LIST    grep -q   SOURCE   then   echo  matched   else   echo  no match   fi

User · Answer

expr is used instead of   rather than inside it  and variables are only expanded inside double quotes  so try this   if expr match   LIST    SOURCE   then   But I m not really clear what SOURCE is supposed to represent   It looks like your code will read in a pattern from standard input  and exit if it matches a database alias  otherwise it will echo  ok    Is that what you want

User · Answer

Well  what about something like this   PS3  Select database or  lt Q gt  to quit    select DB in db1 db2 db3  do         REPLY        Q     amp  amp  break    echo  Should backup  DB     done

User · Answer

You can also compare with wildcards   if      LIST        SOURCE

User · Answer

You can use  index  if you only want to find a single character  e g    LIST  server1 server2 server3 server4 server5  SOURCE  3  if expr index   LIST    SOURCE   then     echo  match      exit -1 else     echo  no match  fi   Output is   23 match

[linux] How to find substring inside a string (or how to grep a variable)?

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