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Full Discussion: Search: find current line, then search back
Top Forums Shell Programming and Scripting Search: find current line, then search back Post 302879662 by alister on Friday 13th of December 2013 03:18:49 PM
Old 12-13-2013
Quote:
Originally Posted by in2nix4life
Not a one-liner, but it does the job
I disagree. One of the few things we know about the data is that a matching pair is ordered. Your code does not guarantee that a last fetch precedes its new = 0 counterpart.


Quote:
Originally Posted by in2nix4life
Code:
# get current working directory and
# change to it
cwd=$(pwd)
cd $cwd

Why change to the current directory? It's already the current directory. Am I missing something?

There is actually a bug in that cd. If the current directory is foo bar, and if there exists a directory named foo, cd $cwd will change to an unintended directory, because the variable expansion isn't double-quoted.


Quote:
Originally Posted by in2nix4life
Code:
for p in ${PATTERN[@]}
do
    ...
    awk "/$srchPattern/{print}" $f
done

If there are P patterns, P+1 passes will be necessary. Hopefully it's a small dataset with few patterns. Your approach could be reimplemented to always finish in 2 passes.


Quote:
Originally Posted by in2nix4life
Code:
    p=$(echo $p | sed 's#\([]/&[]\)#\\\1#g')

Escaping characters for a regular expression engine is a bug-prone procedure that yields brittle solutions.

A case in point: sed 's#\([]/&[]\)#\\\1#g' will add a backslash before each ampersand. Since ampersands are not an AWK ERE metacharacter, \& is an undefined sequence. An AWK implementation is allowed to either silently ignore the backslash or it can choose to abort or it can do ... whatever it wants.

I prefer to avoid this type of manual escaping as much as possible.

Regards,
Alister
 

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