为什么这个sed语句不起作用？

Question

I have been working with regular expressions for the past couple days in class. I cannot determine why this expression doesn't work. I am looking for expressions like the following:

value = (struct node){ 5, NULL};
value2 = (structname){ 1, 2 }; 
*pointer = ( bla ){3,4};

Here is the expression I am using:

sed -n '/^[*0-9A-Za-z_]+ *= *( *[0-9A-Za-z_]+ *[0-9A-Za-z_]* *) *{[0-9A-Za-z, ]};/p'     structfile

What am I missing because it returns nothing. Also a side note I have used [^,] in some expressions and I still get lines with , s. What am I missing?

Answer 1

You need to escape + ; and fix {[0-9A-Za-z, ]} to {[0-9A-Za-z, ]*} .

sed -n '/^[*0-9A-Za-z_]\+ *= *( *[0-9A-Za-z_]\+ *[0-9A-Za-z_]* *) *{[0-9A-Za-z, ]*};/p' structfile


me@localhost:~$ cat structfile 
value = (struct node){ 5, NULL};
value2 = (structname){ 1, 2 }; 
*pointer = ( bla ){3,4};
not astruct
notastructstr =

me@localhost:~$ sed -n '/^[*0-9A-Za-z_]\+ *= *( *[0-9A-Za-z_]\+ *[0-9A-Za-z_]* *) *{[0-9A-Za-z, ]*};/p' structfile
value = (struct node){ 5, NULL};
value2 = (structname){ 1, 2 }; 
*pointer = ( bla ){3,4};

Answer 2

This might work for you (GNU sed):

sed '/^\S\+\s\+=\s\+(\s*\S\+\(\s\+\S\+\)\?\s*){\s*\S\+\s*,\s*\S\+\s*};/!d' file

• Start by building a loose regexp using only whitespace ( \\s ), non-whitespace ( \\S ) and literals ( = , ( , ) , { , } and ; )
• Determine if the above are 1-or-more, zero-or-more or zero-or-one eg one-or-more whitespace would be represented by \\s\\+ , zero-or-more non-whitespace would be \\S* and zero-or-one grouped would be \\(\\s\\+\\S\\+\\)\\?
• Try and anchor the regexp using ^ for start of string, $ end of string and in a multiline regexp \\n for newline
• Build the regexp slowly, left to right, checking each piece as you go along
• Once you have a working version replace individual whitespace/non-whitespace by more specific character classes
• Further refine the one-or-more classes to a specific range or number eg one-to-three ( \\{1,3\\} ) or 3 ( \\{3\\} ) of course a single class, literal or group need not be qualified

HTH