Shell Script compare file content with a string

Question

I have a String "ABCD" and a file test.txt. I want to check if the file has only this content "ABCD". Usually I get the file with "ABCD" only and I want to send email notifications when I get anything else apart from this string so I want to check for this condition. Please help!

Solution 1

Update: My original answer would unnecessarily read a large file into memory when it couldn't possibly match. Any multi-line file would fail, so you only need to read two lines at most. Instead, read the first line. If it does not match the string, or if a second read succeeds at all, regardless of what it reads, then send the e-mail.

str=ABCD
if { IFS= read -r line1 &&
     [[ $line1 != $str ]] ||
     IFS= read -r $line2
   } < test.txt; then
    # send e-mail
fi 

---

Just read in the entire file and compare it to the string:

str=ABCD
if [[ $(< test.txt) != "$str" ]]; then
    # send e-mail
fi

Solution 2

Something like this should work:

s="ABCD"
if [ "$s" == "$(cat test.txt)" ] ;then
    :
else
    echo "They don't match"
fi

Solution 3

str="ABCD"
content=$(cat test.txt)
if [ "$str" == "$content" ];then
    # send your email
fi

Solution 4

if [ "$(cat test.tx)" == ABCD ]; then
           # send your email
else
    echo "Not matched"
fi

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Comments

[neverMind9]

This is the better solution.

[Andrei LED]

Second option also allows to assert multiline text file content

[Andreas Løve Selvik]

I had to do if [[ "$(< test.txt)" != "$str" ]]; then to get the second option to work properly for multiline files. Note the quotes.

[Tomas Reimers]

I think you may need to add a not to your if statement? The author sounds as if they want to send the email if the contents does not match