shell中expr强大功能（1）

kaiser_cn

　　EXPR(1)                          User Commands                         EXPR(1)
　　NAME
　　expr - evaluate expressions
　　SYNOPSIS
　　expr EXPRESSION
　　expr OPTION
　　DESCRIPTION
　　--help display this help and exit
　　--version
　　output version information and exit
　　Print  the  value of EXPRESSION to standard output.  A blank line below
　　separates increasing precedence groups.  EXPRESSION may be:
　　ARG1 | ARG2
　　ARG1 if it is neither null nor 0, otherwise ARG2
　　ARG1 & ARG2
　　ARG1 if neither argument is null or 0, otherwise 0
　　ARG1 < ARG2
　　ARG1 is less than ARG2
　　ARG1 = ARG2
　　ARG1 is greater than or equal to ARG2
　　ARG1 > ARG2
　　ARG1 is greater than ARG2
　　ARG1 + ARG2
　　arithmetic sum of ARG1 and ARG2
　　ARG1 - ARG2
　　arithmetic difference of ARG1 and ARG2
　　ARG1 * ARG2
　　arithmetic product of ARG1 and ARG2
　　ARG1 / ARG2
　　arithmetic quotient of ARG1 divided by ARG2
　　ARG1 % ARG2
　　arithmetic remainder of ARG1 divided by ARG2
　　STRING : REGEXP
　　anchored pattern match of REGEXP in STRING
　　match STRING REGEXP
　　same as STRING : REGEXP
　　substr STRING POS LENGTH
　　substring of STRING, POS counted from 1
　　substr STRING POS LENGTH
　　substring of STRING, POS counted from 1
　　index STRING CHARS
　　index in STRING where any CHARS is found, or 0
　　length STRING
　　length of STRING
　　+ TOKEN
　　interpret TOKEN as a string, even if it is a
　　keyword like `match' or an operator like `/'
　　( EXPRESSION )
　　value of EXPRESSION
　　Beware that many operators need to be escaped  or  quoted  for  shells.
　　Comparisons are arithmetic if both ARGs are numbers, else lexicographi‐
　　cal.  Pattern matches return the string matched between \(  and  \)  or
　　null;  if  \( and \) are not used, they return the number of characters
　　matched or 0.
　　Exit status is 0 if EXPRESSION is neither null nor 0, 1  if  EXPRESSION
　　is  null  or  0,  2 if EXPRESSION is syntactically invalid, and 3 if an
　　error occurred.
　　AUTHOR
　　Written by Mike Parker, James Youngman, and Paul Eggert.
　　REPORTING BUGS
　　Report expr bugs to bug-coreutils@gnu.org
　　GNU coreutils home page:
　　General help using GNU software:
　　Report expr translation bugs to
　　COPYRIGHT
　　Copyright &copy; 2010 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.
　　SEE ALSO
　　The full documentation for expr is maintained as a Texinfo manual.   If
　　the  info  and  expr  programs are properly installed at your site, the
　　command
　　info coreutils 'expr invocation'
　　should give you access to the complete manual.
　　GNU coreutils 8.5                February 2011                         EXPR(1)
　　Manual page expr(1) line 63/109 (END)