Stream Editor in the UNIX Shell - The hold space and whole scripts
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You can use the hold space with the following commands:
Command
Effect
N
Take a new line from the input.
Append a new line at the end of the current pattern space.
Append a new line to the end of the space.
If this is the last input line, the sed will exit.
P
Print the content of the pattern space until the first new line.
h
Print the pattern space to the hold space.
H
Append with a new line the content of the pattern space to the hold space.
g
Get. It will get the content of the hold space to the pattern space.
G
Append the content of the hold space with a new line to the end of the pattern space. (The new line will be prior to the hold content).
x
Switch the content of the hold space and the pattern space.
D
Print a line from the pattern space, all the way to the first new line. If there is more text in the pattern space, it will start a new cycle without reading the next token from the input.
For example, let's look at the simulation of the tac tool. The tac tool will list the content of a file line by line in reverse order:
#!/bin/sed -nf
#The simulation of the tac tool with the help
#Usage:
# cat file | sed -nf rev.sed
1!G #Unless we are at the first line get back the whole hold
#space
$p #This will print the last line from the pattern space
h #put back all to the hold space
Alternatively:
cat file | sed -n -r '1h;1!{x;H};${g;p}'
In the end, let me present a more complex script that takes advantage of the sed tool. It is about a little text editor tool that will add a new line, delete a line, and list the file.
#!/bin/bash
if [ $# -ne 1 ]
then
echo A single parameter is required
exit 1
fi
if (file $1 | egrep "file")
then
touch "$1"
fi
select menu in "New line" "Delete" "List" "End"
do
case $REPLY in
1) echo New line
read newLine
sed -i '$a'"$newLine" "$1"
;;
2) echo Delete
read row
sed -i -n "$row"'d' "$1";;
3) echo list
read from to
sed -n "$from"','"$to"' p' "$1"
;;
4) echo End
exit 1;;
?)echo Invalid Choice;;
esac
done
I will give you the privilege to try out and learn on the upper script. With this, I thank you for your attention and hope that you learned a lot of useful information today. I invite you to rate my article. In addition, you can ask questions related to this article here in the comment area.blog. Next week I will continue with the awk, so if you are interested make sure to check back. Live With Passion!
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