BASH replace two variables in order with loop

Question

I have two files with this structure:

File1.txt:

1,,
1,,
1,,
1,,
1,,
1,,
1,,
1,,
2,,
2,,
2,,
2,,
2,,
2,,
3,,
3,,
3,,
3,,
4,,
4,,
4,,
4,,
4,,
5,,
5,,
5,,
5,,

File2.txt:

I want to replace File1.txt numbers with File2.txt in order, so it would look like this:

0015,,
0015,,
0015,,
0015,,
0015,,
0015,,
0015,,
0015,,
0016,,
0016,,
0016,,
0016,,
0016,,
0016,,
0017,,
0017,,
0017,,
0017,,
0018,,
0018,,
0018,,
0018,,
0018,,
0019,,
0019,,
0019,,
0019,,

And I haven't found an effective loop to do so, any help will be appreciated

Thank you.

Cyrus · Accepted Answer · 2015-04-18 09:32:44Z

3

Update:

With GNU sed and bash (process substitution):

sed -n -f <(sed -n "s|^\([^,]\)\(.*\)$|\1{h;s/[0-9]*/\&\2/p;g}|p" File1.txt) File2.txt > File_new.txt

See: man sed and info sed

edited Apr 18, 2015 at 9:32

answered Apr 17, 2015 at 19:38

Cyrus

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2 Comments

Ramirous Over a year ago

That's great!! is there any way to keep the changes in File1.txt? (I ask this because File1 actually has many columns in csv format)

Peter Cordes Over a year ago

This runs a new sed process for every line of the input file. It would be more efficient to do it in shell, or even to start up perl.

Peter Cordes · Accepted Answer · 2015-04-17 20:01:40Z

0

Read the 2nd file into a linear array. Use it as a lookup table, index by the first field of the 1st file. With non-numeric keys, use an associative array instead.

readarray -t mapping < File2.txt  # -t strips trailing newlines

while IFS=  read -r l;
    do pref=${l%%,*};
    printf '%s%s\n' "${mapping[pref-1]}" ",${l#*,}"
done < File1.txt

Or "${l#[0-9]}", or whatever other way will be most future-proof for getting the part of the line you aren't replacing.

Or shopt -s extglob and "${l#+([0-9])}" (extglob version of the regex [0-9]+)

This is pure-bash, no external commands. If the input files are potentially large, the same algorithm in perl would probably be faster. bash isn't great for speed.

edited Apr 17, 2015 at 20:01

answered Apr 17, 2015 at 19:51

Peter Cordes

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