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GNU shell utilities

5.4.4 Examples of using expr

Here are a few examples, including quoting for shell metacharacters.

To add 1 to the shell variable foo, in Bourne-compatible shells:

foo=`expr $foo + 1`

To print the non-directory part of the file name stored in $fname, which need not contain a /.

expr $fname : '.*/\(^.*\)' '^|' $fname

An example showing that \+ is an operator:

expr aaa : 'a\+' => 3

expr abc : 'a\(.\)c' => b expr index abcdef cz => 3 expr index index a error--> expr: syntax error expr index quote index a => 0