Replace first few lines with first few lines from other file

Question

I am working on Linux. I have 2 files - file1.dat and file2.dat.

cat file1.dat
1
2
3
4
5
6
7
8
9
10

and for file2:

cat file         


        

Answer 1

awk is your friend

Script

# awk 'NR==FNR && FNR<=3 || NR>FNR && FNR>4' file2 file1

Output

1a
2a
3a
5
6
7
8
9
10

Tips

• NR - Total number of records processed
• FNR - Total number of records processed but resets when reading a new file.
• When a condition evaluates to true and no extra commands are given,awk just prints.

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All good :-)