[英]for loop without List in the shell script
我正在閱讀來自 OpenFoam 的 shell 腳本( /opt/openfoam8/bin/foamCleanPath
) 。 在這個腳本中,有一段代碼:
for dir
do
....
done
我在以下屏幕截圖中標記了代碼段。
但我想知道為什么它不像for dir in someList
,並且上面的代碼段中沒有dir
的定義。 我應該怎么理解?
這是源代碼:
#!/bin/sh
#------------------------------------------------------------------------------
# ========= |
# \\ / F ield | OpenFOAM: The Open Source CFD Toolbox
# \\ / O peration | Website: https://openfoam.org
# \\ / A nd | Copyright (C) 2011-2018 OpenFOAM Foundation
# \\/ M anipulation |
#------------------------------------------------------------------------------
# License
# This file is part of OpenFOAM.
#
# OpenFOAM is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
# for more details.
#
# You should have received a copy of the GNU General Public License
# along with OpenFOAM. If not, see <http://www.gnu.org/licenses/>.
#
# Script
# foamCleanPath
#
# Description
# Usage: foamCleanPath [-strip] path [wildcard] .. [wildcard]
#
# Prints its argument (which should be a ':' separated path)
# without all
# - duplicate elements
# - elements whose start matches a wildcard
# - inaccessible directories (with the -strip (at your option)
#
# Note
# - this routine will fail when directories have embedded spaces
# - false matches possible if a wildcard contains '.' (sed regex)
# - the wildcards can themselves can be written together and separated
# by colons or whitespace
#------------------------------------------------------------------------------
usage() {
cat <<USAGE
Usage: ${0##*/} [OPTION] path [wildcard1] .. [wildcardN]
options:
-strip remove inaccessible directories
-help print the usage
Prints its argument (which should be a ':' separated list) cleansed from
- duplicate elements
- elements whose start matches one of the wildcard(s)
- inaccessible directories (with the -strip option)
Exit status
0 on success
1 for miscellaneous errors.
2 initial value of 'path' is empty
USAGE
}
error() {
usage 1>&2
exit 1
}
unset strip
# parse options
while [ "$#" -gt 0 ]
do
case "$1" in
-h | -help)
usage && exit 0
;;
-strip)
strip=true
shift
;;
-*)
error
;;
*)
break
;;
esac
done
[ "$#" -ge 1 ] || error
dirList="$1"
shift
[ -n "$dirList" ] || exit 2 # quick exit on empty 'dirList'
##DEBUG echo "input>$dirList<" 1>&2
# preserve current IFS and split on colon or whitespace
oldIFS="$IFS"
IFS=': '
# "wildcard1 ... wildcardN" may have been passed as a single parameter
# or may contain ':' separators
set -- $*
# strip out wildcards via sed
while [ "$#" -ge 1 ]
do
wildcard=$1
shift
##DEBUG echo "remove>$wildcard<" 1>&2
if [ -n "$wildcard" ]
then
dirList=$(echo "$dirList:" | sed -e "s|${wildcard}[^:]*:||g")
fi
done
# split on ':' (and on space as well to avoid any surprises)
IFS=': '
set -- $dirList
##DEBUG echo "intermediate>$dirList<" 1>&2
# rebuild the list from scratch
unset dirList
for dir
do
##DEBUG echo "check>$dir<" 1>&2
#- dirs must exist
if [ -e "$dir" ]
then
#- no duplicate dirs
duplicate=$(echo " $dirList " | sed -ne "s: $dir :DUP:p")
if [ ! "$duplicate" ]
then
dirList="$dirList $dir"
fi
elif [ "$strip" != true ]
then
# Print non-existing directories if not in 'strip' mode.
dirList="$dirList $dir"
fi
done
# split on whitespace
IFS=' '
set -- $dirList
# rejoin on ':'
IFS=':'
dirList="$*"
# restore IFS
IFS="$oldIFS"
##DEBUG echo "output>$dirList<" 1>&2
echo "$dirList"
#------------------------------------------------------------------------------
引用Bash 手冊頁,這是實現/bin/sh
的更常見的 shell 之一:
for name [ [ in [ word... ] ]; ] do list; done
in
之后的單詞列表被擴展,生成項目列表。 變量名依次設置到這個list的每個元素,每次都會執行list 。 如果省略in
字,則for
命令對設置的每個位置參數執行一次list [...]
因此,如果您省略in...
部分,循環將遍歷在當前上下文中設置的位置 arguments ( $1
, $2
, ...)。 在您的情況下,這將是作為命令行 arguments 給出的通配符列表。
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