The pipe character (|) tells the regex engine to match any of the passed strings. So, if one of them exists, that is enough for the pattern to match. It's like a logical OR between the passed strings:
$ echo "welcome to shell scripting" | awk '/Linux|bash|shell/{print $0}'$ echo "welcome to bash scripting" | awk '/Linux|bash|shell/{print $0}'$ echo "welcome to Linux scripting" | awk '/Linux|bash|shell/{print $0}'$ echo "welcome to shell scripting" | sed -r -n '/Linux|bash|shell/p'$ echo "welcome to bash scripting" | sed -r -n '/Linux|bash|shell/p'$ echo "welcome to Linux scripting" | sed -r -n '/Linux|bash|shell/p'
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