EXPR(1) EXPR(1) expr - expr expr --help --version 1 | 2 1 null 012 1 & 2 null 01 0 1 < 2 1 2 1 <= 2 1 2 1 = 2 1 2 1 != 2 1 2 1 >= 2 1 2 1 > 2 1 2 1 + 2 1 2 1 - 2 1 2 1 * 2 1 2 1 / 2 1 2 1 % 2 1 2 : match " : " substr 1 index CHARS CHARS 0 length + TOKEN TOKEN 'match' '/' ( ) shell \( \) null \( \) 0 null 0 0 null 0 1 1 3 Mike Parker, James Youngman Paul Eggert GNU coreutils Copyright (C) 2022 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later . This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. info '(coreutils) expr invocation' man man https://github.com/man-pages-zh/manpages- zh GNU coreutils 9.1 20229 EXPR(1)