sed – How to Remove the Very Last Occurrence of a String (Comma) in a File Using sed

sed

I have a very large csv file. How would you remove the very last , with sed (or similar) ?

...
[11911,0,"BUILDER","2014-10-15","BUILDER",0,0],
[11912,0,"BUILDER","2014-10-15","BUILDER",0,0],
[11913,0,"BUILDER","2014-10-15","BUILDER",0,0],
]

Desired output

...
[11911,0,"BUILDER","2014-10-15","BUILDER",0,0],
[11912,0,"BUILDER","2014-10-15","BUILDER",0,0],
[11913,0,"BUILDER","2014-10-15","BUILDER",0,0]
]

The following sed command will delete the last occurrence per line, but I want per file.

sed -e 's/,$//' foo.csv

Nor does this work

sed '$s/,//' foo.csv

Best Answer

Using `awk`

If the comma is always at the end of the second to last line:

$ awk 'NR>2{print a;} {a=b; b=$0} END{sub(/,$/, "", a); print a;print b;}'  input
[11911,0,"BUILDER","2014-10-15","BUILDER",0,0],
[11912,0,"BUILDER","2014-10-15","BUILDER",0,0],
[11913,0,"BUILDER","2014-10-15","BUILDER",0,0]
]

Using `awk` and `bash`

$ awk -v "line=$(($(wc -l <input)-1))" 'NR==line{sub(/,$/, "")} 1'  input
[11911,0,"BUILDER","2014-10-15","BUILDER",0,0],
[11912,0,"BUILDER","2014-10-15","BUILDER",0,0],
[11913,0,"BUILDER","2014-10-15","BUILDER",0,0]
]

Using `sed`

$ sed 'x;${s/,$//;p;x;};1d'  input
[11911,0,"BUILDER","2014-10-15","BUILDER",0,0],
[11912,0,"BUILDER","2014-10-15","BUILDER",0,0],
[11913,0,"BUILDER","2014-10-15","BUILDER",0,0]
]

For OSX and other BSD platforms, try:

sed -e x -e '$ {s/,$//;p;x;}' -e 1d  input

Using `bash`

while IFS=  read -r line
do
    [ "$a" ] && printf "%s\n" "$a"
    a=$b
    b=$line
done <input
printf "%s\n" "${a%,}"
printf "%s\n" "$b"

Related Solutions

Use sed to Print Lines Until Last Occurrence of a Pattern

Try this:

$ tac infile | sed -n '/fish/,$p' |tac

In general case if you run below sed command, you will get all line from first matched pattern to end of input file.

$ sed -n '/fish/,$p' file

this is a some fish
this is a fishie
this is a fish
this is a lion
this is a cat

So my solution is: If we run tac command on input file your last matched pattern will change to as first pattern. see the result of tac infile:

$ tac infile

this is a cat
this is a lion
this is a fish
this is a fishie
this is a some fish
this is a goat
this is a cow

The tac command is the same as cat command, while tac prints files in reverse order.

Now if we run our first sed command, you will get all lines first matched pattern to end of input file. like:

$ tac infile | sed -n '/fish/,$p'
this is a fish
this is a fishie
this is a some fish
this is a goat
this is a cow

Ok, finished. We only need to run tac command again to reverse back the lines to original order:

$ tac infile | sed -n '/fish/,$p' |tac
this is a cow
this is a goat
this is a some fish
this is a fishie
this is a fish

Done!

Sed – How to Replace the Last Occurrence of a Character in a String

You can do it with single sed:

sed 's/\(.*\)-/\1 /'

or, using extended regular expression:

sed -r 's/(.*)-/\1 /'

The point is that sed is very greedy, so matches as many characters before - as possible, including others -.

$ echo 'swp-RedHat-Linux-OS-5.5.0.0-03' | sed 's/\(.*\)-/\1 /'
swp-RedHat-Linux-OS-5.5.0.0 03

Best Answer

Using awk

Using awk and bash

Using sed

Using bash