Defined variable in bash loop cannot be compared correctly

Question

Creat 2 files at first:

cat <<'EOF'> test
f u u 1624268497
f3 u2 u2 1624268498
EOF


cat <<'EOF'> test_new
f u4 u5 16242684973
f4 u2 u2 1624268498
f3 u2 u2 1624268498
EOF

I want to loop files to list the unique element of test_new,script as below:

##!/bin/bash
added=()
while read F_NEW O_NEW G_NEW P_NEW; do
    exist=0
    while read F O G P; do
    #exist in both old & new
    if [[ $F_NEW == $F ]]; then
        exist=1
        break
    fi
    #   echo "tester: $F"
    done < test
    if [ $exist == 0 ]; then
    echo $F_NEW
        added+=($F_NEW)
    fi

done < test_new

printf '%s\n' "${added[*]}"

Expect result is:

f4

but I got:

f4 f3

Where is the problem?

but I got: I run your code as is and I got only f4 printed twice. Can't reproduce.. — KamilCuk
– KamilCuk, Commented Jun 24, 2021 at 6:30
I can reproduce the output when I remove the echo $_NEW and add a non-printable character (e.g. $'\x01') before the f3 in test_new. — choroba
– choroba, Commented Jun 24, 2021 at 7:02
I only get f4 displayed twice. If you remove echo $F_NEW I get the expected output f4 — Jean-Loup Sabatier
– Jean-Loup Sabatier, Commented Jun 24, 2021 at 7:39

Raman Sailopal · Accepted Answer · 2021-06-24 09:30:11Z

1

Awk is a good candidate for a problem such as this:

awk 'NR==FNR { arr[$1]=1;next } arr[$1] != "1" { print $1 }' test test_new

Process the test file first (NR==FNR) Create an array called arr keyed by the first space delimited field. Then when processing the test_new file, if there isn't an entry in arr for the first field, print the first field.

answered Jun 24, 2021 at 9:30

Raman Sailopal

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2 Comments

kittygirl Over a year ago

If loop is long,I tried awk 'NR==FNR { arr[$1]=1;next } arr[$1] != "1" { added+= $1 }' test test_new printf '%s\n' "${added[@]}" but there's no output.what's the problem?

Raman Sailopal Over a year ago

try readarray -t added <<< "$(awk 'NR==FNR { arr[$1]=1;next } arr[$1] != "1" { added+= $1 }' test test_new)";printf '%s\n' "${added[@]}"

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