Shell test to find a pattern in a string

I just wanted to ask whether there is any command which would work on common shells (bash, dash, kornshell)? It is supposed to check if the line variable contains any part of the path.

if [[ $line =~ "$PWD"$ ]] ;then

Answers:

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Method 1

In any POSIX-compatible shell you can do:

case $line in (*"$PWD"*)
#    whatever your then block had
;;esac

This works in bash, dash, and just about any other shell you can name.

It can also be used to handle multiple possibilities easily. For example:

case $line in 
(*"$PWD"*)
    echo $PWD match!
;;
(*"$OLDPWD"*)
    echo $OLDPWD match!
;;
(*)
    ! echo no match!
;;esac

You can also use alternation:

case $line in (*"$PWD"*|*"$OLDPWD"*)
    echo '$OLDPWD|$PWD match!'
;;esac

Note the use of quoting above:

1. case $line ...
   • The object of a case statement will not be split on either $IFS or be used as a pattern for filename gen. This is similar to the way the left argument in a [[ test is treated.
2. (*"$PWD"*)
   • Here also a shell expansion is not subjected to either $IFS or filename generation – an unquoted expansion will neither split nor glob.
   • But an unquoted expansion here might be construed as a pattern rather than a literal string though, and so an expansion might mean more than one thing depending on whether or not it is quoted.
   • It is important to quote any variable used in a pattern that should be literally interpreted, in the same way you would quote pattern chars which you wanted interpreted literally.
   • For example, if $PWD contained a * and was not quoted it would be construed as a pattern object and not as a literal * to be searched for.

Method 2

Yes, recent versions of bash can do this:

$ pwd
/home/terdon
$ line="I'm in /home/terdon"
$ [[ "$line" =~ "$PWD"$ ]] && echo yes
yes

The same syntax works in zsh and ksh but not in dash. As far as I know, dash has no such capabilities.

Note that your regex is checking whether the variable $line ends with $PWD. To check if $PWD matches anywhere in $line, remove the $:

$ line="I'm in /home/terdon, are you?"
$ [[ "$line" =~ "$PWD" ]] && echo yes
yes

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0