[bash] insert string randomly in the file?

czezz · 05-01-2018, 05:39 AM

Hi can someone help me how to insert string "insert this " in a random position/anywhere in the file xx?
Just once insert.

My sed insert it in each line at the beginning of the file.

Code:

cat xx |  sed 's/^/insert this /'
insert this sdgerger
insert this gjrth
insert this sdgesgA
insert this dfsdkfsdhfkjhsg
insert this Ber
insert this sgsergerhgierug

syg00 · 05-01-2018, 06:01 AM

Probably not - if it is to be random, how can we possibly help.
Be exact, not hopelessly vague with your request.
- only at the beginning of line ?
- which line ? Is this known in advance ?.

czezz · 05-01-2018, 06:34 AM

Hi Syg,
I want to add string "insert this " anywhere/randomly but not at the beginning or end of the file.
Somewhere in the middle of the file.

wpeckham · 05-01-2018, 06:42 AM

What you describe is interesting. There are ways to insert a string at an ARBITRARY location, but a "random" location is a complex concept. I doubt you can achieve random in this context.

czezz · 05-01-2018, 06:54 AM

Hi,
i think im getting closer.
Now I need to figure out how to add "insert this " only in 1, randomly chosen, line. Any hints?

Code:

random_position="$(shuf -i 0-10 -n 1)"
sed "s/^\(.\{"${random_position}"\}\)./\1insert this /" xx
sdgerger
gjrth
sdgesgA
dfsdkfsdinsert this fkjhsg
Ber
sgsergerinsert this gierug

Turbocapitalist · 05-01-2018, 07:04 AM

If you are running bash or zsh you can use the pseudo-random environment variable $RANDOM to insert at a random line number:

Code:

#!/bin/zsh

file="czezz.data";

l=$(wc -l < $file);

let "r = $RANDOM % $l + 1";

sed -e "$r iInserted Line" < $file;

For more about arithmetic see https://ryanstutorials.net/bash-scri...arithmetic.php
Or "man bash" or "man zsh"

And be sure to read "man sed" about the i and a commands.

ksh might be an option but standard POSIX shells are out for this particular approach.

czezz · 05-01-2018, 09:43 AM

Thanks for your effort.
It ADDs a new line whereas I want to add a string to already existing line (randomly chosen), somewhere in the middle of this line (random position).

What I managed to produce (based on yours) is: choose random line number and add STRING at the end of it.
That's close what I need.
If I only knew now how to add STRING somewhere in the middle (random position) of this line. (which I actual achieved in my previous post but dont know how to merge it with this one)

Code:

#!/bin/bash

file="czezz.data";
l=$(wc -l < $file);
let "r = $RANDOM % $l +1";
echo $r;

sed "${r}s/$/ insert this/" < $file;

Turbocapitalist · 05-01-2018, 10:04 AM

Just add another read, maybe like this:

Code:

#!/bin/zsh

file="czezz.data";

l=$(wc -l < $file);

let "r = $RANDOM % $l + 1";

w=$(sed -e "$r!d" < $file | wc -m);

let "s = $RANDOM % $w + 1";

sed "s/^\(.\{"${s}"\}\)/\1insert this/" < $file;

The first pass picks a random line. The second pass picks a random character from that line. The third pass does the insertion.

It's inefficient, so maybe the knowledgeable people can say something.

ondoho · 05-01-2018, 10:06 AM

instead of using sed (which is line-centric), have you tried reading the file character by character, injecting your string at a random position, then writing it back?
seems like the most straightforward shell scripting alternative to me.

keefaz · 05-01-2018, 10:44 AM

Quote:

Originally Posted by czezz

Thanks for your effort.
It ADDs a new line whereas I want to add a string to already existing line (randomly chosen), somewhere in the middle of this line (random position).

What I managed to produce (based on yours) is: choose random line number and add STRING at the end of it.
That's close what I need.
If I only knew now how to add STRING somewhere in the middle (random position) of this line. (which I actual achieved in my previous post but dont know how to merge it with this one)

Code:

#!/bin/bash

file="czezz.data";
l=$(wc -l < $file);
let "r = $RANDOM % $l +1";
echo $r;

sed "${r}s/$/ insert this/" < $file;

Merged:

Code:

random_position=$(shuf -i 0-10 -n 1)
l=$(wc -l $file);
let "r = $RANDOM % $l +1";

sed "${r}s/^\(.\{"${random_position}"\}\)./\1insert this /" < $file;

xamaco · 05-01-2018, 10:51 AM

Code:

shuf -n1 your-file