#!/bin/bash
 
# ideone boilerplate - we can't write files in the home directory;
# so create a temporary directory for our files instead
t=$(mktemp -d -t ideone.XXXXXXXXXXXX) || exit
trap 'rm -rf "$t"' ERR EXIT
cd "$t"
 
init() {
    printf 'one %s\n' {1..5} >test1.txt
    printf 'two %s\n' {1..50} >test2.txt
}
 
init
nl *.txt
 
cat <<\_ >demo.py
# insert contents of "test1.txt" into "test2.txt" at line 20
with open("test1.txt", "r") as f1:
    t1 = f1.readlines()
with open("test2.txt", "r") as f2:
    t2 = f2.readlines()
t2.insert(20, t1)
with open("test2.txt", "w") as f2:
    f2.writelines(t2)
_
 
python3 demo.py 2>&1 || echo '** Original failed'
 
cat <<\_ >demo2.py
# insert contents of "test1.txt" into "test2.txt" at line 20
with open("test2.txt", "r+") as f2:
    for x in range(20):
        f2.readline()   # skip past early lines
    pos = f2.tell() # remember insertion position
    f2_remainder = f2.read()    # cache the rest of f2
    f2.seek(pos)
    with open("test1.txt", "r") as f1:
        f2.write(f1.read())
    f2.write(f2_remainder)
_
python3 demo2.py
 
nl test2.txt
echo '** Incorrect output above; try fixed version'
init
 
cat <<\_ >demo3.py
with open("test2.txt", "r+") as f2:
    for x in range(20):
        f2.readline()   # skip past early lines
    pos = f2.tell() # remember insertion position
    f2_remainder = f2.read()    # cache the rest of f2
    f2.seek(pos)
    with open("test1.txt", "r") as f1:
        for line in f1:
            f2.write(line)
    f2.write(f2_remainder)
_
 
python3 demo3.py
 
nl test2.txt
 
echo "** pavot.kutaj's version"
 
cat <<\_ >demo4.py
def main():
    with open("test2.txt", mode="rt", encoding="utf-8") as f1:
        source_list = [line.strip() for line in f1.readlines()]
 
    with open("test1.txt", mode="rt", encoding="utf-8") as f2:
        insert_list = [line.strip() for line in f2.readlines()]
 
    pos = source_list.index("two 21")
    source_list[pos: pos] = insert_list #a bit counter-intuitive slicing-approach
 
    with open("test2.txt", mode="w", encoding="utf-8") as f1:
        f1.write("\n".join(source_list))
 
if __name__ == "__main__":
    main()
_
 
 
init
 
python3 demo4.py
 
nl test2.txt

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