在Linux shell编程中，经常会用到判断字符串是否相等，可用于判断字符串是否相等的操作符有‘-eq’（相等）, ‘-ne’（不等于）, ‘-lt’（小于）, ‘-le’（小于或等于）, ‘-gt’（大于）或‘-ge’（大于或等于），以及=，==，!=，<，>。
在bash指南中，字母操作符和符号操作符的两端的参数英语表达式不相同，符号操作符用的是string，字母操作符用的是arg。
# http://www.gnu.org/software/bash/manual/bashref.html
-
string1==string2
-
string1=string2 -
True if the strings are equal. ‘=’ should be used with the
testcommand for POSIX conformance. -
string1!=string2 -
True if the strings are not equal.
-
string1<string2 -
True ifstring1sorts beforestring2lexicographically.
-
string1>string2 -
True ifstring1sorts afterstring2lexicographically.
-
arg1OParg2 -
OPis one of ‘-eq’, ‘-ne’, ‘-lt’, ‘-le’, ‘-gt’, or ‘-ge’. These arithmetic binary operators return true ifarg1is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal toarg2, respectively.Arg1andarg2may be positive or negative integers.
在实际编程中发现，当用字母操作符，虽然效果与符号操作符相同，但会产生一个错误提示“[[: arg2: syntax error: operand expected (error token is "arg2")”。
如原文为
|
1
|
[[
"$1"
-
eq
""
]] &&
echo
"delete all spaces and comments of specialized file, using with $@ filename"
&&
exit
1
|
修改为
|
1
|
[[
"$1"
==
""
]] &&
echo
"delete all spaces and comments of specialized file, using with $@ filename"
&&
exit
1
|
就不再提示了。
附带一个实用小脚本，用途：grep掉空格和注释符（#），简单实用。
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4
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#!/bin/bash
# delete all spaces and comments of specialized file, using with $@ filename
[[
"$1"
==
""
] &&
echo
"delete all spaces and comments of specialized file, using with $@ filename"
&&
exit
1
grep
-
v
\
# $1 | grep -v ^$
|
添加到操作系统中：
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1
2
3
4
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7
8
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10
|
cat
> delsc.sh << eof
#!/bin/bash
# delete all spaces and comments of specialized file, using with $@ filename
[[
"\$1"
-==
""
]] &&
echo
"delete all spaces and comments of specialized file, using with \$@ filename"
&&
exit
1
grep
-
v
\
# \$1 | grep -v ^$
eof
chmod
+x .
/delsc
.sh
\
mv
delsc.sh
/usr/local/bin/delsc
which
delsc
cat
/usr/local/bin/delsc
|
用法：
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1
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delsc filename
|
