CODEWITHSUNDEEP
linuxshell
yaxin
yaxin

Reputation: 1588

How to keep blank lines in the end of a file when I user cat command in shell script

the file a.txt has two blank lines at the end

[yaxin@oishi tmp]$ cat -n a.txt 
     1  jhasdfj
     2  
     3  sdfjalskdf
     4  
     5

and my script is:

[yaxin@oishi tmp]$ cat t.sh 
#!/bin/sh
a=`cat a.txt`
a_length=`echo "$a" | awk 'END {print NR}'`
echo "$a"
echo $a_length


[yaxin@oishi tmp]$ sh t.sh 
jhasdfj

sdfjalskdf
3

open debug

[yaxin@oishi tmp]$ sh -x t.sh 
++ cat a.txt
+ a='jhasdfj

sdfjalskdf'
++ echo 'jhasdfj

sdfjalskdf'
++ awk 'END {print NR}'
+ a_length=3
+ echo 'jhasdfj

sdfjalskdf'
jhasdfj

sdfjalskdf
+ echo 3
3

the cat command steal the blank lines at the end of the file.How to solve this problem.

Upvotes: 5

Views: 1509

Answers (2)

anubhava
anubhava

Reputation: 785276

You don't need cat command here, directly use awk like this:

awk 'END {print NR}' a.txt

Your problem is in storing the cat's output in a shell variable. Even this will give right output (though case of UUOC):

cat a.txt | awk 'END {print NR}'

Update: When you try to do this:

a=`cat a.txt`

OR else:

a=$(cat a.txt)

Pitfall is that the process substitution i.e. command inside reverse quote like you have or in $() strips trailing newlines.

You can do this trick to get trailing newlines stored in a shell variable:

a=`cat a.txt; echo ';'`
a="${a%;}"

Test the variable value:

echo "$a"
printf "%q" "$a"

Then output will show newlines as well:

jhasdfj

sdfjalskdf


$'jhasdfj\n\nsdfjalskdf\n\n\n'

Upvotes: 1

choroba
choroba

Reputation: 241918

The cat command does not steal anything. It is the command substitution that does. man bash says:

Bash performs the expansion by executing command and replacing the command substitution with the standard output of the command, with any trailing newlines deleted. Embedded newlines are not deleted

If you want to store an output of a command to a variable, you might add && echo . after the command, store the output and remove the final ..

Also, to count the number of lines in a file, the cannonical way is to run wc -l:

wc -l < a.txt

Upvotes: 3

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