在 Bash 的“while”循环中使用“if”
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Using 'if' within a 'while' loop in Bash
提问by capser
I have these diff results saved to a file:
我将这些差异结果保存到文件中：
bash-3.00$ cat /tmp/voo
18633a18634
> sashabrokerSTP
18634a18636
> sashatraderSTP
21545a21548
> yheemustr
I just really need the logins:
我只需要登录：
bash-3.00$ cat /tmp/voo | egrep ">|<"
> sashaSTP
> sasha
> yhee
bash-3.00$
But when I try to iterate through them and just print the names I get errors.
I just do not understand the fundamentals of using "if" with "while loops".
Ultimately, I want to use the whileloop because I want to do something to the lines - and apparently whileonly loads one line into memory at a time, as opposed to the whole file at once.
但是当我尝试遍历它们并只打印名称时，我得到了错误。我只是不明白将“if”与“while循环”一起使用的基本原理。最终，我想使用while循环，因为我想对行做一些事情 - 显然一次while只将一行加载到内存中，而不是一次加载整个文件。
bash-3.00$ while read line; do if [[ $line =~ "<" ]] ; then echo $line ; fi ; done < /tmp/voo
bash-3.00$
bash-3.00$
bash-3.00$ while read line; do if [[ egrep "<" $line ]] ; then echo $line ; fi ; done < /tmp/voo
bash: conditional binary operator expected
bash: syntax error near `"<"'
bash-3.00$
bash-3.00$ while read line; do if [[ egrep ">|<" $line ]] ; then echo $line ; fi ; done < /tmp/voo
bash: conditional binary operator expected
bash: syntax error near `|<"'
bash-3.00$
There has to be a way to loop through the file and then do something to each line. Like this:
必须有一种方法来遍历文件，然后对每一行做一些事情。像这样：
bash-3.00$ while read line; do if [[ $line =~ ">" ]];
then echo $line | tr ">" "+" ;
if [[ $line =~ "<" ]];
then echo $line | tr "<" "-" ;
fi ;
fi ;
done < /tmp/voo
+ sashab
+ sashat
+ yhee
bash-3.00$
采纳答案by John Kugelman
You should be checking for >, not <, no?
你应该检查>，不是<，不是吗？
while read line; do
if [[ $line =~ ">" ]]; then
echo $line
fi
done < /tmp/voo
回答by anubhava
Do you really need regex here? The following shell glob can also work:
你真的需要正则表达式吗？以下 shell glob 也可以工作：
while read line; do [[ "$line" == ">"* ]] && echo "$line"; done < /tmp/voo
OR use AWK:
或使用 AWK：
awk '/^>/ { print "processing: " $ grep -oP '> \K\w+' <<END
18633a18634
> sashabrokerSTP
18634a18636
> sashatraderSTP
21545a21548
> yheemustr
END
}' /tmp/voo
回答by glenn Hymanman
grepwill do:
grep会做：
sashabrokerSTP
sashatraderSTP
yheemustr
