最后一个特定字符后的表达 [英] Expression after last specific character
问题描述
foo="/sdf/here/jfds"
bar="${foo##*/}"
谁能解释" $ {foo ## */}
"表达作品?我知道它将在最后一个正斜杠(即jfds)之后返回字符串.但是,我不知道它是怎么做的,或者这种类型的表达式叫什么?
Can anyone explain how the "${foo##*/}
" expression works? I understand it will return the string after the last forward slash (i.e. jfds). However, I have no idea how it does or what this type of expression is called?
推荐答案
它是几种shell功能之一,通常称为 shell扩展.这种特定的扩展被称为 parameter 扩展*.
It is one of several shell features, generically called shell expansion. This particular expansion is called parameter expansion*.
您可以将这种特殊的Shell扩展形式视为左截断字符串函数.您必须使用如图所示的花括号(这不是可选的).
You can think of this particular shell expansion form as a left-truncate string function. You must use the curly braces as shown (that is not optional)..
当您仅使用一个#
时,表示仅左截断随后出现的模式的 first (直到结束的}
.当您使用两个 ##
时,表示左截断所有连续模式匹配.echo $ {var#*/} 是 b/c
... echo $ {var ## */}
返回 c
When you use only one #
, it means left-truncate only the first occurrence of the pattern which follows (up to the closing }
. When you use two ##
, it means left-truncate all consecutive pattern-matches. The result of var="a/b/c"; echo ${var#*/}
is b/c
... echo ${var##*/}
returns c
.
有一个补充的右截.它使用%
而不是#
...(我记住",这是因为#
就像bash注释;始终在剩下).
There is a complementary right-truncate. It uses %
instead of the #
... (I "remember" which is which because #
is like a bash comment; always on the left).
*
被视为bash通配符扩展.
The *
is treated as a bash wildcard expansion.
这是所有shell扩展的列表,按优先级顺序显示.
Here is a list of all shell expansions, presented in precedence order.
扩展顺序为:
1. brace expansion ... prefix{-,\,}postfix # prefix-postfix prefix,postfix
.. {oct,hex,dec,bin} # oct hex dec bin
. {a..b}{1..2} # a1 a2 b1 b2
. {1..04} # 01 02 03 04
. {01..4} # 01 02 03 04
. {1..9..2} # 1 3 5 7 9
. \$\'\\x{0..7}{{0..9},{A..F}}\' # $'\x00' .. $'\x7F'
2. tilde expansion .... ~ # $HOME
... ~axiom # $(dirname "$HOME")/axiom
... ~fred # $(dirname "$HOME")/fred
.. ~+ # $PWD (current working directory)
.. ~- # $OLDPWD (previous working directory. If OLDPWD is unset,
~- is not expanded. ie. It stays as-is,
regardless of the state of nullglob.)
# Expansion for Directories in Stack. ie.
# The list printed by 'dirs' when invoked without options
. ~+N # Nth directory in 'dirs' list (from LHS)
. ~-N # Nth directory in 'dirs' list (from RHS)
3. parameter expansion .... ${VAR/b/-dd-}
... ${TEST_MODE:-0}
.. ${str: -3:2} # note space after :
. ${#string}
4. (processed left-to-right)
variable expansion
arithmetic expansion
command substitution
▶5. word splitting # based on $IFS (Internal Field Seperator)
▷6. pathname expansion
according to options such as:
nullglob, GLOBIGNORE, ...and more
# Note: ===============
▶ 5. word splitting ↰
▷ 6. pathname expansion ↰
# ===================== ↳ are not performed on words between [[ and ]]
这篇关于最后一个特定字符后的表达的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!