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Question

这是Bash变量声明语句：

foo='b'`    `'ar'

效率低于此：

foo='bar'

这种格式化“挂起”或“对齐”缩进(行续)的方式：

a_long_variable_name='a seemingly infinitely long '`
                    `'string requiring continuatio'`
                    `'n on the next line...'

产卵子壳，浪费资源，或以任何方式影响性能，除了烦扰那些不喜欢它的形式(反？)可读性？

效率如:计算机效率，而不是“人类键入许多字符，创造空间为基础的，无偿的维护债务”。

能否很容易地证明对性能的影响(或缺乏影响)？

Answer 1

tester1() {
  for i in {1..1000}; do
    a_long_variable_name='a seemingly infinitely long '`
                        `'string requiring continuation'`
                        `'on the next line...'
    echo $a_long_variable_name > tmp 
  done
}

tester2() {
  for i in {1..1000}; do
    a_long_variable_name="a seemingly infinitely long\
string requiring continuation\
on the next line..."
    echo $a_long_variable_name > tmp 
  done
}

echo tester1
time tester1
echo tester2
time tester2

结果

tester1

real    0m1.878s
user    0m0.209s
sys     0m0.566s

tester2

real    0m0.335s
user    0m0.026s
sys     0m0.078s

所有这些都有类似于案例2的时间：

read -r -d '' a_long_variable_name <<EOF
    a seemingly infinitely long
    string requiring continuation
    on the next line...
EOF

a_long_variable_name="a seemingly infinitely long\
                      string requiring continuation\
                      on the next line..."

Answer 2

如果我需要它，我可能会这样构建字符串：

x='a seemingly infinitely long '
x="$x"'string requiring continuatio'
x="$x"'n on the next line...'

a_long_variable_name="$x"

或者那个主题的小变体。或者，我会在每一行上重复长变量名。下面是我使用的一个真正的脚本-它为我列出了相关的环境变量：

informix1="DB[^=]|DELIMIDENT=|SQL|ONCONFIG|TBCONFIG|INFOR"
informix2="CLIENT_LOCALE=|GL_|GLS8BITSYS|CC8BITLEVEL|ESQL|FET_BUF_SIZE="
informix3="INF_ROLE_SEP=|NODEFDAC=|ONCONFIG|OPTCOMPIND|PDQ|PSORT"
informix4="PLCONFIG|SERVER_LOCALE|FGL|C4GL|NE_"
informix5="TCL_LIBRARY|TK_LIBRARY|TERM=|TERMCAP=|TERMINFO="
informix="$informix1|$informix2|$informix3|$informix4|$informix5"
system1="COLLCHAR=|LANG=|LC_"
system2="(DY)?LD_LIBRARY_PATH(_[63][42])?=|PATH=|SHLIB_PATH=|LIBPATH="
system="$system1|$system2"
jlss="IX([A-Z]|D(32|64)?)="

env |
${EGREP:-egrep} "^($informix|$system|$jlss)" |
sort

(当MacOSX10.7.x egrep由于“太大”而停止使用该表达式时，切换使用哪个egrep程序的能力就变得必要了。)