CODEWITHSUNDEEP
awksed
Vituvo
Vituvo

Reputation: 1048

How to delete the last nth characters from the nth line with sed?

Ubuntu 16.04
Bash 4.4

I want to delete the last nth characters from the nth line. Here is a simple file and the last 4 characters on each line is the number 4. 

root@0o0o0o0o0 ~/.ssh # cat remove.txt
00000000004444
55555555555555555555555554444
222222222222222224444
000033334444
111114444

To remove the last 4 characters from each line I can execute sed -i 's/....$//' remove.txt

root@0o0o0o0o0 ~/.ssh # sed -i 's/....$//' remove.txt
root@0o0o0o0o0 ~/.ssh # cat remove.txt
0000000000
5555555555555555555555555
22222222222222222
00003333
11111

But what if I wanted to remove the last 4 characters from the 4th line, removing the 3's so the file would look like this:

0000000000
5555555555555555555555555
22222222222222222
0000
11111

Upvotes: 0

Views: 228

Answers (2)

RavinderSingh13
RavinderSingh13

Reputation: 133770

Could you please try following in awk. Written and tested in GNU awk.

awk -v line="4" -v nofChar="4" '
{
  sub(".{"nofChar"}$","")
}
FNR==line{
  sub(".{"nofChar"}$","")
}
1
'  Input_file

Detailed explanation: 

awk -v line="4" -v nofChar="4" '   ##Starting awk program and setting line variable value, nofChar variable value here.
{
  sub(".{"nofChar"}$","")          ##Substituting last nofChar number of characters at last of the each line here.
}
FNR==line{                         ##Checking if this is same line which OP wants to do 2nd time substitution.
  sub(".{"nofChar"}$","")          ##Substituting last nofChar number of characters at last of the each line here.
}
1                                  ##Mentioning 1 will print edited/non-edited line.
'  Input_file                      ##Mentioning Input_file name here.

2nd solution: In case number of characters in all lines are different than specific line then try following. One has to change variable named nofUsualChar value.

awk -v line="4" -v nofChar="4" -v nofUsualChar="4" '
{
  sub(".{"nofUsualChar"}$","")
}
FNR==line{
  sub(".{"nofChar"}$","")
}
1
'  Input_file

Upvotes: 4

Cyrus
Cyrus

Reputation: 88999

With GNU sed:

sed -i 's/....$//; 4s/....$//' file

4s/....$// limits search and replace to 4th row.

See: man sed and info sed

Upvotes: 5

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