Bash script file reading

Question

I'm trying to select certain text from an output file.

I'm reading my file as follows:

while read line 
do
    if [ "$line" == "SUMMARY OF POLARIZATION CALCULATION" ]; then
        break
    fi
done < tutorial1/Tutorial1_1.out

When the loop reaches that "Summary" line, i need to read only the next 9 lines. I'm trying to use a for loop but i'm not sure how to use it:

for i in {1..9}
do
    read line < tutorial1/Tutorial1_1.out
    echo $line >> Summary.out
done

My output is as follows:

next is setrmt
next is setrmt
next is setrmt
next is setrmt
next is setrmt
next is setrmt
next is setrmt
next is setrmt
next is setrmt

But i need it to be the next 9 lines after the "SUMMARY" statement. Please help.

Where's the file you're reading really? Is it in tutorial1/Tutorial1_1.out or in ../Tutorial1_1.out? These are different files unless tutorial1 is a symlink to the parent directory. — Jonathan Leffler
– Jonathan Leffler, Commented Sep 2, 2014 at 16:18

clt60 · Accepted Answer · 2014-09-02 16:39:13Z

3

You can use the -A parameter for the grep command like:

grep -A9 "SUMMARY OF POLARIZATION CALCULATION"

from the man:

-A NUM, --after-context=NUM

          Print NUM lines of trailing context after matching lines.

demo:

while read -r line
do
    echo "$line"
done < <(grep -A9 "SUMMARY OF POLARIZATION CALCULATION" filename | tail -9)

for the next input file

before1
before2
before3
before4
before5
before6
SUMMARY OF POLARIZATION CALCULATION
line1
line2
line3
line4
line5
line6
line7
line8
line9
line10
line11
line12

prints:

line1
line2
line3
line4
line5
line6
line7
line8
line9

or simply:

 grep -A9 "SUMMARY OF POLARIZATION CALCULATION" ../Tutorial1_1.out | tail -9 >> Summary.out

edited Sep 2, 2014 at 16:39

answered Sep 2, 2014 at 16:27

clt60

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Comments

Anton B · Accepted Answer · 2014-09-02 16:41:58Z

2

You can't redirect again. That reopens the file at the beginning. Do the second block inside the first and use the same file descriptor:

while read line 
do
    if [ "$line" == "SUMMARY OF POLARIZATION CALCULATION" ]; then
        for i in {1..9}
        do
            read line
            echo $line >> Summary.out
        done
        break
    fi
done < tutorial1/Tutorial1_1.out

edited Sep 2, 2014 at 16:41

Anton B

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answered Sep 2, 2014 at 16:18

Dark Falcon

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1 Comment

chepner Over a year ago

You can also replace the entire for loop with head when sharing the file descriptor. { while read line; do if [ ... ]; then break; fi; done; head -9 > Summary.out; } < tutorial1/Tutorial1_1.out.

Louis Kottmann · Accepted Answer · 2014-09-02 16:27:50Z

0

Let's try a clean solution:

1) find the line number of the line that contains the string you want. You could do this by implementing a counter, but this is better:

linenr=$(grep -n -m 1 "SUMMARY OF POLARIZATION CALCULATION" <your file name here> | cut -d':' -f1)

2) calculate the number of the last line you want:

let "lastlinenr = $linenr + 9"

3) fetch the lines and write them to a file:

cat <your file name here> | sed -n "$linenr","$lastlinenr"p > <your destination file here>

answered Sep 2, 2014 at 16:27

Louis Kottmann

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1 Comment

Anton B Over a year ago

I tried this method, but it returns an empty string.

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