在bash中IFS是内部的域分隔符，manual中对其的叙述如下：
IFS The Internal Field Separator that is used for word splitting after expansion and to split lines into words with the read builtin command. The default value is “
如下是一些值得注意的地方。
1. IFS的默认值为：空白（包括：空格，tab, 和新行)，将其ASSII码用十六进制打印出来就是：20 09 0a （见下面的shell脚本）。
2. IFS对空格的空白的处理和其他字符不一样，左右两半的纯空白会被忽略，多个连续的空白被当成一个IFS处理。
3. S*中使用IFS中的第一个字符。
4. awk中的FS（域分隔符）也和IFS有类似的用法和作用。
我写了一个shell脚本来演示IFS的用法和作用，如下：
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748 | #! /bin/bash#author: Jay Ren#date: 2011.12.10 echo "----------------------------------IFS test--------------------------------"echo "default \$IFS is:(ASSII in hexadecimal value)"echo -n "$IFS" | xxd -g 1 | awk -F":" '{print $2}' | awk -F" " '{print $1, $2, $3}'echo "by default, IFS should be a SPACE, a HORIZONTAL TAB, or a LINC FEED." function output_args_one_per_line(){arg_list=$*echo "\$*='$*'"for arg in $arg_listdoecho "[$arg]"done} echo "--------------------------------------------------------------------------"echo "set IFS=' ' #dealing with SPACE in IFS is different with other chars."echo "var=' a b c '"IFS=' 'var=" a b c "output_args_one_per_line $var echo "--------------------------------------------------------------------------"echo "set IFS=':'"echo "var='::a:b::c:::'"IFS=':'var="::a:b::c:::"output_args_one_per_line $var echo "--------------------------------------------------------------------------"echo "set IFS='+:-;' #but \$* just use 1st char in IFS as the separator."echo "var='::a:b::c:::'"IFS='+:-;'var="::a:b::c:::"output_args_one_per_line $var echo "--------------------------------------------------------------------------"echo "set IFS='-+:;' #but \$* just use 1st char in IFS as the separator."echo "var='::a:b::c:::'"IFS='-+:;'var="::a:b::c:::"output_args_one_per_line $var echo "--------------------------The END of IFS test-----------------------------" |
运行这个脚本结果如下：
View Code BASH
12345678910111213141516171819202122232425262728293031323334353637383940414243444546 | master@jay-linux:~/workspace/mygit/shell/sh2011$ ./IFS-test.sh----------------------------------IFS test--------------------------------default $IFS is:(ASSII in hexadecimal value)20 09 0aby default, IFS should be a SPACE, a HORIZONTAL TAB, or a LINC FEED.--------------------------------------------------------------------------set IFS=' ' #dealing with SPACE in IFS is different with other chars.var=' a b c '$*='a b c'[a][b][c]--------------------------------------------------------------------------set IFS=':'var='::a:b::c:::'$*='::a:b::c::'[][][a][b][][c][]--------------------------------------------------------------------------set IFS='+:-;' #but $* just use 1st char in IFS as the separator.var='::a:b::c:::'$*='++a+b++c++'[][][a][b][][c][]--------------------------------------------------------------------------set IFS='-+:;' #but $* just use 1st char in IFS as the separator.var='::a:b::c:::'$*='--a-b--c--'[][][a][b][][c][]--------------------------The END of IFS test----------------------------- |
