This situation is extracted from a larger context. My intention for now is to escape the forward slashes in the path of a filename. (Ultimately the LINEs will come from a file.)
Code:
while read LINE ; do
sed 's/\//\\\//g' <<< "$LINE" # ok
escaped=`sed 's/\//\\\//g' <<< "$LINE"` # error message
echo $escaped
done <<here
==: dir1/dir2/file1 dir3/dir4/file2
==: dir5/dir6/file3 dir1/file4
==: dir3/file5 dir3/file6
==: dir1/file4 dir5/dir6/file3
==: dir3/dir4/file2 dir1/dir2/file1
==: dir3/file6 dir3/file5
here
While the direct sed output looks the way I want the next line where I try to assign that to a variable gives me an error message:
I find out it doesn't really work if I redirect the file into a while-loop that uses read to read a line, like this:
Code:
while read $LINE ; do
swap column 2 with column 3
remove swapped line from file (using sed)
done < file
I got the idea because while read works line by line from the beginning of the file the swapped line is always located behind the other one so if I remove it read will never see it. But apparently the entire original file is still available to read no matter what I remove.
Backticks have been deprecated for a long time. They offer no advantage over $( ... ) and have quoting nesting and escaping issues.
Unless you are writing for a legacy shell like pre-Posix Bourne shell, use $( ... ) instead. I never use them.
Unless you need further line level processing in shell, you could of course use:
Code:
sed 's|/|\\/|g' << "here"
...
here
If you need the line processing in a loop, calling an external program with each iteration is expensive..
If you use bash, ksh93 or zsh as a shell you could use something like this (parameter expansion):
Code:
while read LINE
do
escaped=${LINE//\//\\/}
echo "$escaped"
done << "here"
...
here
-or-
Feed the sed output into a loop (and use read's -r option):
Code:
{
sed 's|/|\\/|g' << "here"
...
here
} |
while read -r LINE
do
echo "processing ${LINE}"
done
--
Note: as was suggested a different delimiter removes the need for the escape for the forward slash, which makes the code more readable. In the examples given there was one escape too many:
Code:
sed 's|/|\\/|g'
Also, to prevent headaches, it is recommended to quote variable expansions, so use:
Code:
echo "$escaped"
or better yet:
Code:
printf "%s\n" "$escaped"
Last edited by Scrutinizer; 12-16-2018 at 11:49 AM..
These 2 Users Gave Thanks to Scrutinizer For This Post:
I find out it doesn't really work if I redirect the file into a while-loop that uses read to read a line, like this:
Code:
while read $LINE ; do
swap column 2 with column 3
remove swapped line from file (using sed)
done < file
I got the idea because while read works line by line from the beginning of the file the swapped line is always located behind the other one so if I remove it read will never see it. But apparently the entire original file is still available to read no matter what I remove.
Is there is a better approach?
Assuming the fields in your input file are whitespace separated, you could try this approach:
Code:
awk '!A[$2,$3]++ && !A[$3,$2]++' file
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12-16-2018
