What does =~ mean in VimScript?

Question

I can't for the life of me find an answer to this either on google or here or in the help files.

if "test.c" =~ "\.c" 

At first I thought =~ mean ends in, but observe these results:

Command                               Result echo "test.c" =~ "\.c"                1 echo "test.c" =~ "\.pc"               0 echo "test.pc" =~ "\.c"               1 echo "testc" =~ "\.c"                 1 echo "ctest" =~ "\.c"                 1 echo "ctestp" =~ "\.pc"               0 echo "pctestp" =~ "\.pc"              0 echo ".pctestp" =~ "\.pc"             0 

An explanation would be great. A link to a site attempting to decipher VimScript would be even better.

Answer 1

From the Vim documentation, it does a pattern match of the right operand (as a pattern) inside the left.

For strings there are two more items:

    a =~ b      matches with     a !~ b      does not match with 

The left item "a" is used as a string. The right item "b" is used as a pattern, like what's used for searching. Example:

    :if str =~ " "     :  echo "str contains a space"     :endif     :if str !~ '\.$'     :  echo "str does not end in a full stop"     :endif 

You might try your test cases again. I get, for example, inconsistent with yours:

echo ".pctestp" =~ "\.pc"             1 

And double-quotes vs single quotes seem to affect how the backslash is interpreted:

echo "test.pc" =~ "\.c"               1 echo "test.pc" =~ '\.c'               0