With a shell script?

女狼一共舞

How to write a shell script to display the odd number of lines (1, 3, 5 .... lines) for a given file?

1231456

sed -n "p; n" / etc / profile

1231456

awk '{if (NR% 2 == 1) print $ 0}' / etc / profile

skywater00

If it is a text file, you can process it directly
linenum = 1
lines = `cat filename`
for line in $ {lines}; do
   if [$ [$ {linenum}% 2] -ne 0]; then
           echo $ {line}
   fi
   linenum = $ [$ {linenum} +1]
done

skywater00

Of course, the previous methods are all correct.

女狼一共舞

Excuse me, how does the value of the variable line change?

女狼一共舞

#! / bin / sh
echo "input filename"
read fname
linenum = 1
lines = 'cat filename'
for linenum in $ {lines}; do
   if [$ [$ {linenum}% 2] -ne 0]; then
           echo $ {linenum}
   fi
   linenum = $ [$ {linenum} +1]
done


Is there something wrong with this?
Why can't I debug it?

女狼一共舞

#! / bin / sh
echo "input filename"
read fname
linenum = 1
lines = 'cat fname'
for linenum in $ {lines}; do
     if [$ [$ {linenum}% 2] -ne 0]; then
                     echo $ {linenum}
     fi
     linenum = $ [$ {linenum} +1]
done
 
 
Is there something wrong with this?
Why can't I debug it?

skywater00

Written like this $ fname
And your cat is also wrong. It is not a single quote, but a back quote. It is generally the one to the left of 1 on the keyboard, which means executing a shell command. It can also be replaced with $ ()
linenum = 1
read filename
lines = `cat $ {filename}`
for line in $ {lines}; do
if [$ [$ {linenum}% 2] -ne 0]; then
echo $ {line}
fi
linenum = $ [$ {linenum} +1]
done

skywater00

However, the above code is actually problematic, that is, there can be no more tokens such as spaces in a line, otherwise an error will occur. The better method is the1231456method.