using =~ operator to match output of a command and grab group from it. Code is as follows:

Comamndout=$(cmd) Match=‘^hello world’ If $Comamndout =~ $Match; then echo something fi

Commandout is in pattern Something Hello world

But if statement is failing. Is bash regex support multiline search with everyline start with ^ and end with $.

CodePudding user response：

No, the =~ operator doesn't perform a multiline search. A newline must be matched literally:

string=$(cmd)
regexp='(^|'$'\n'')hello world'

if [[ $string =~ $regexp ]]; then
  echo matches
fi

CodePudding user response：

=~ would treat multiple lines as one line.

if [[ $(echo -e "abc\nd") =~ ^a.*d$ ]]; then
  echo "find a string '$(echo -e "abc\nd")' that starts with a and ends with d"
fi

Output:

find a string 'abc
d' that starts with a and ends with d

P.S.
When processing multiple lines, it is common to use grep or read with either re-direct or pipeline.

• For a grep and pipeline example:

  # to find a line start with either a or e
  echo -e "abc\nd\ne" | grep -E "^[ae]"
  

  Output:

  abc
  e
  

• For a read and redirect example:

  while read line; do
    if [[ $line =~ ^a} ]] ; then
      echo "find a line '${line}' start with a"
    fi
  done <<< $(echo -e "abc\nd\ne")
  

  Output:

  find a line 'abc' start with a
  

P.S. -e of echo means translate following \n into new line. -E of grep means using the extended regular expression to match.