How can I read/print a specific column using bash script?

Question

My code and input file are below. But my code doesn't print what I want. It prints all contents of the input file. But I want to print only "standard deviation" column. How can I do this using bash script?

My code:

#!/bin/bash
file="/path/input.txt"
while IFS= read -r line
do
   echo "$line" >> out.xvg
done <"$file"

input.txt:

The terms of the GNU Lesser General Public License
as published by the Free Software Foundation; either version
of the License.

Read 2 sets of 201 points, dt = 0.01


                       standard      
set      average       deviation    

a1   2.445857e+01   2.145235e+01   
a2  -1.158344e+02   5.452454e+01  
a3   2.314415e+04   3.652432e+05  
a4  -5.153647e-03   7.235728e-02

Requested output:

2.145235e+01   
5.452454e+01  
3.652432e+05  
7.235728e-02

Updated:

sed '/a1/,$!d' input.xvg | sed '$d' | awk '{print $3}' > output.txt

This code works but it ignores the last line of the file. I checked the input file. That is missing the newline character after its last line. But I want to print all lines of "standard deviation" column. How can I fix this problem?

if you can use awk awk 'NR>10{print $3}' file

user4453924
– user4453924

2015-02-26 13:34:40 +00:00
Commented Feb 26, 2015 at 13:34 — user4453924
– user4453924, Commented Feb 26, 2015 at 13:34

Will · Accepted Answer · 2022-09-02 09:09:21Z

1

With the cut argument you can solve your problem :

echo "$line" | tr -s " " | cut -d " " -f 3

tr -s " " removes all the " " (spaces) char to only one.
cut -d defines your delimiter
-f choses the colomn your want to print out (fieldset)

edited Sep 2, 2022 at 9:09

answered Feb 26, 2015 at 11:54

Will

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5 Comments

Will Over a year ago

well isn't "trim" but "tr", my bad. I edit my response

selami Over a year ago

It works now. But It doesn't print only "standard deviation" column. It also prints some characters like "sets, deviation.."

Will Over a year ago

My solution will be to use this command on your input file tail -n +9 input.txt > output.txt, and make your while/done on the output.txt file (9 is the first line which will be copy in ouput.txt)

ccarton Over a year ago

@William The tail operation can also be done on the stdin of the while loop directly. done < <(tail -n +9 "$file")

selami Over a year ago

It is solved: sed '/a1/,$!d' input.xvg | sed '$d' | awk '{print $3}' > output.txt

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