Linux bash script file concatenation

Question

Hi in my script i've concatenated two files into a new file called output.txt. Am having trouble checking that output.txt file does exist to then print a "concatenation successful" message. The concatenation appears to work and create a new file.

cat $file1 $file2 >> output.txt     

file3="$output.txt"                #incorrect?

if [ -e $file3 ]                             
then
    echo "concatenation of files successful"
fi

Remove the dollar sign: file3="output.txt". $output is being replaced by a variable named output (which does not exist in the snippet posted here). If you move the file3 variable above cat, you can use it for the output redirection as well to avoid repeating the filename twice. — cfillion
– cfillion, Commented Apr 2, 2019 at 23:46

sashimi · Accepted Answer · 2019-04-02 23:58:51Z

1

Should be:

file3="output.txt"
cat $file1 $file2 >> $file3

if [ -f $file3 ]; then
    echo "concatenation of files successful"
fi

edited Apr 2, 2019 at 23:58

answered Apr 2, 2019 at 23:43

sashimi

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4 Comments

perennial_noob Over a year ago

That -f doesn't fix the problem. In fact -e works just fine too.

sashimi Over a year ago

Just fixed it - now should be ok

perennial_noob Over a year ago

I changed to upvote because @cfillion only added his answer as a comment. So even though this is edited this now is the correct answer. @phebus - note that in a shell script you don't need to have ; after if and before then

cfillion Over a year ago

It now tries to run a command named file3. There should not be spaces around the equal sign.

itChi · Accepted Answer · 2019-04-03 07:12:17Z

1

file3="output.txt"
cat $file1 $file2 >> $file3

if [ $? == 0 ]; then
    echo "concatenation of files successful"
fi

Checking the file's existence doesn't mean that the files concatenated successfully. It means that the file exists.

Consider that:

cat $file1 $file2(missing) >> $file3
cat $file1(missing) $file2 >> $file3

would make $file3 exist.

Checking last operation exit value with $? accounts for the whole operation working successfully.

Also, unless you're specifically looking to append >> to existing file, you will ALWAYS append. So your file will always exist after the first operation.

answered Apr 3, 2019 at 7:12

itChi

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Comments

SachinPatil4991 · Accepted Answer · 2019-04-03 07:43:53Z

0

In single line


cat $file1 $file2 >> output.txt && echo 'Success' || echo 'Failed'

answered Apr 3, 2019 at 7:43

SachinPatil4991

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