Here's my question:
e.g
echo 123\< abc\\\ efg
The output should be
123< abc\ efg
My regex in lex file is
[^\n ]*[\\]+[^\n]
If I use this regex, my output is going to be
123< abc\ efg
which is wrong. Can anybody tell me how to match \(space) and regular (space) respectively?
Thanks!
I believe that what you are looking for is a flex regular expression which will match a single shell token which does not contain quotes or other such complications.
Note that the characters which automatically terminate tokens are the following: ();<>&| and whitespace. (The bash manual says space and tab, but I'm pretty sure that newline also separate words.)
Such a regular expression is possible, but (imho) it is of little use, partly because it doesn't take quoting (or bracketing: a$(echo foo)b is a single word), and partly because the resulting word needs to be rescanned for escape characters. But whatever. Here's a sample flex regex:
([^();<>&|\\[:space:]]|\\(.|\n))+
That matches any number of consecutive instances of:
Your regex is correct. When you type at the prompt
echo 123\< abc\\\ efg
the following happens:
bash replaces \< with < (without the backslash, bash would treat < as in input redirection operator.
bash replaces \\ with a single literal \
bash replaces '\ ` with a single literal space.
bash calls the echo command, passing it 2 arguments: 123< and abc\ efg.
echo produces the output 123< abc\ efg, a single string with a single space separating its two arguments.
Based on your regular expression, it looks like the string output in my step 5 above is what is stored in your file. From those 13 bytes, it would find 3 valid tokens: 123<, abc\, and efg. If it prints them to standard output as a single string with a space separating each token, you would see 123< abc\ efg. (There should be two spaces following that backslash; I can't seem to get multiple spaces to display.)
echo 123\< abc\\\ efgandecho "123\< abc\\\ efg"; in the firstbashhas a chance to process the escaped characters in the string before displaying them. So the question is, how are you calling your lexer in order to produce123< abc\ efg?