Info Catalog coreutils: Relations for expr coreutils: expr invocation

coreutils: Examples of expr

 
 16.4.4 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 + index a
      ⇒ 0
 

Info Catalog coreutils: Relations for expr coreutils: expr invocation