shell中expr强大功能（1）
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
Printthevalue 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 escapedorquotedforshells.
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, 1ifEXPRESSION
isnullor0,2 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 © 2010 Free Software Foundation, Inc. LicenseGPLv3+:GNU
GPL version 3 or later .
Thisisfreesoftware:youare 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
theinfoandexprprograms 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)
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