awk: re-order columns using printf

echo 1.txt | awk 'BEGIN{FS="\t"} {printf "%s\t%s\n", $2, $1}'

Shell scripting: enclose all lines with quotes

• Using awk:

  awk '{print "\""$0"\""}' input.txt
  

  or if ignore empty lines:

  awk 'NF {print "\""$0"\""}' input.txt
  

• Or using sed:

  sed -i.bak 's/^/"/; s/$/"/' input.txt
  

  or if ignore empty lines:

  sed -i.bak 's/^..*$/"&"/' input.txt
  

awk: print the last two columns

cat file | awk '{print $(NF-1) $NF}'

or

awk '{print $(NF-1) $NF}' file

shell script: read lines from file in a while loop

• by piping cat:

  cat /path/to/file | while read line
  do
      echo $line
  done
  

• by redirecting the file:

  while read line
  do
      echo $line
  done < /path/to/file
  

• by using awk:

  awk '{print $0}' /path/to/file
  

• by using head an tail:

  f=/path/to/file
  total=$(wc -l $f)
  n=0
  while [ $n -lt $total ]
  do
      let n++
      line=$(head -n $n $f | tail -1)
      echo ${line}
  done
  

awk: add a column based on the test of existing columns

E.g. we have a text file, numbers.txt, see below:

1 2
3 4
5 6

and we want to add the 3rd column, its value is yes/no. If the sum of the 1st column and the 2nd column is greater than 3, the value of the 3rd column is yes, otherwise no.

1 2 no
3 4 yes
5 6 yes

The following command:

awk '{printf "%s %s %s\n",$1,$2,($1+$2>3)?"yes":"no"}' numbers.txt > new_numbers.txt

will do the work.

awk: append a column that sums up existing columns

E.g. we have a text file, numbers.txt, see below:

1 2
3 4
5 6

and we want to add the 3rd column which is the sum of values of the first and the second columns.

1 2 3
3 4 7
5 6 11

The following command:

awk '{print $1 " " $2 " " int($1+$2)}' numbers.txt > new_numbers.txt

will do the work.
Or, the following command do the same thing:

awk '{printf "%s %s %d\n",$1,$2,int($1+$2)}' numbers.txt > new_numbers.txt