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!

Are you using a bash script? You can grab the contents of test.txt by doing `cat test.txt` and then compare with your string. — user3885927, Aug 31 '16 at 21:55
Please [edit] your question to show [what you have tried so far](http://whathaveyoutried.com). You should include a [mcve] of the code that you are having problems with, then we can try to help with the specific problem. You should also read [ask]. — Toby Speight, Aug 31 '16 at 22:12

chepner · Accepted Answer · 2018-07-19T15:50:19.300

28

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

edited Jul 19 '18 at 15:50

answered Aug 31 '16 at 21:59

chepner

497,756
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Second option also allows to assert multiline text file content – Andrei LED Nov 29 '19 at 11:13
1

I had to do `if [[ "$(< test.txt)" != "$str" ]]; then` to get the second option to work properly for multiline files. Note the quotes. – Andreas Løve Selvik Feb 26 '20 at 22:30

score 15 · Answer 2 · answered Aug 31 '16 at 22:01

15

Something like this should work:

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

answered Aug 31 '16 at 22:01

NickD

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score 9 · Answer 3 · answered Sep 01 '16 at 03:07

9

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

answered Sep 01 '16 at 03:07

Scott Wang

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1
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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 – Tomas Reimers Jan 13 '21 at 19:42

score 3 · Answer 4 · answered Dec 18 '18 at 10:00

3

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

answered Dec 18 '18 at 10:00

sachin_ur

2,375
14
27

We'll See · Answer 5 · 2023-03-04T08:41:15.393

0

Solution using grep:

    if grep -qe ^$MY_STR$ myfile; then \
        echo "success"; \
    fi

edited Mar 04 '23 at 08:41

answered Mar 04 '23 at 07:46

We'll See

122
1
8

This matches for all files where `MY_STR` is a sub-string, right? Poster want to match only files where `MY_STR` is the entire content. `^` and `$` is anchors for a line, the the entire file. – Lii Aug 29 '23 at 08:59

Shell Script compare file content with a string

5 Answers5