Shell Programming and Scripting

This deletes all of the spaces, if any, at the beginning of every line:

Code:

sed -e 's/^ *//'

This portion of the same command deletes all the spaces, if any, at the end of every line:

Code:

-e 's/ *$//'

This could mean almost anything depending on what variable file1 is equal to. But !d means delete every line outside of that address range. The q quits after the first match.

Code:

sed "$file1!d;q"<file2

This is curious. '\011' is a TAB character. Modern GNU sed accepts \t for a tab character, but that wasn't so in olden days. Maybe someone had to go through that gymnastic to get a tab character into a sed expression. It looks like it would delete every tab character in the file.

Code:

sed 's/'"$(echo '\011')"'//g' file

Can someone explain wat below set of commands do?

Code:

chkcntr=1
while [ $chkcntr -le $filcntr ]
do
  filename=`sed "$chkcntr!d;q"<filenamesCnt.txt`
  filename=`sed "$chkcntr!d;q"<filenamesCnt.txt`
  filename=`echo $filename | sed -e 's/^ *//' -e 's/ *$//'`
  chkcntr=`expr $chkcntr + 1`
done

What shell are you running this in?
When I experimented with part of it in bash, the exclamation mark (!) was expanded to trash.

Very clever bash users can use the exclamation mark to include command history in the current command. I've never learned to use it because it looks like more bother than worth. Maybe the author intended to use history. The fact that the first line inside the do-loop is repeated suggests he might have. If so, I have no idea what it does. If not, there's no point in repeating the line.

But if we assume it was not intended to be that tricky, it could be made useful by changing it:

Code:

# Replace this:
  filename=`sed "$chkcntr!d;q"<filenamesCnt.txt`
# with this:
  filename=`sed $chkcntr'!d;q'<filenamesCnt.txt`

This line removes starting and ending space characters from the filename.

Code:

  filename=`echo $filename | sed -e 's/^ *//' -e 's/ *$//'`

The line with expr could just as easily be done this way:

Code:

  ((chkcntr++))