CODEWITHSUNDEEP
linuxbash
Bouncer00
Bouncer00

Reputation: 123

Removing strings from file using bash script

I want to delete a specific strings from file. I try to use:

for line3 in $(cat 2.txt)
do
   if grep -Fxq $line3 4.txt
      then
      sed -i /$line3/d 4.txt
   fi
done

I want this code to delete lines from 4.txt if they are also in 2.txt, but this loop deletes all lines from 4.txt and I have no idea why. Can someone tell what is wrong with this code ?

2.txt:

a
ab
abc

4.txt:

a
abc
abcdef

Upvotes: 1

Views: 294

Answers (4)

anubhava
anubhava

Reputation: 785098

You can do this via single awk command:

awk 'ARGV[1] == FILENAME && FNR==NR {a[$1];next} !($1 in a)' 2.txt 4.txt
abcdef

To store output back to 4.txt use:

awk 'ARGV[1] == FILENAME && FNR==NR {a[$1];next} !($1 in a)' 2.txt 4.txt > _tmp && mv _tmp 4.txt

PS: Added ARGV[1] == FILENAME && to take care of empty file case as noted by @pjh below.

Upvotes: 1

gboffi
gboffi

Reputation: 25023

Look ma', only sed... 

sed $( sed 's,^, -e /^,;s,$,$/d,' 2.txt ) 4.txt
  1. Transform each line in 2.txt in a sed command, e.g., abc -> -e /^abc$/d
  2. Give the list of sed commands to an instance of sed operating on 4.txt

To store output back to 4.txt use:

sed -i $( sed 's,^, -e /^,;s,$,$/d,' 2.txt ) 4.txt

edit: while I love my answer on an aesthetic base, please don't try this at home! see pjh comment below for a detailed rationale of the many ways in which my microscript may fail

Upvotes: 0

pjh
pjh

Reputation: 8064

Using just Bash (4) builtins:

declare -A found
while IFS= read -r line || [[ $line ]] ; do found[$line]=1 ; done <2.txt
while IFS= read -r line || [[ $line ]] ; do
    (( ${found[$line]-0} )) || printf '%s\n' "$line"
done <4.txt

The '[[ $line ]]' tests are to handle files with unterminated last lines.

Use 'printf' instead of 'echo' in case any of the output lines begin with 'echo' options.

Upvotes: 0

Vytenis Bivainis
Vytenis Bivainis

Reputation: 2376

grep -F -v -x -f 2.txt 4.txt

or

grep -Fvxf 2.txt 4.txt

or

fgrep -vxf 2.txt 4.txt

Upvotes: 1

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