Member Avatar for seemit

Hi,
I want to append each line in a file with string "foo foo" if number of charcters in the line are 4000. There can be n number of lines and this scenario applies to all lines. .. any takes? i want shell to do it.

-Seemit

  • 2 Contributors
  • 5 Replies
  • 108 Views
  • 1 Day Discussion Span
  • Latest Post Latest Post by seemit

Dani AI

Generated

Both and solved this with shell read loops. That works for small files, but there are a few practical pitfalls to watch for: shell read can mangle leading/trailing whitespace and backslashes unless used as IFS= read -r, loops in shell are much slower than stream tools for large files, and counting "characters" vs bytes matters for multibyte (UTF‑8) data.

A compact, robust streaming approach is awk (fast, handles long lines better than a shell loop). For plain text where counting characters in the current locale is fine:

awk 'length($0) == 4000 { print; next } { print $0 "foo foo" }' input.txt > output.txt

length($0) counts characters in the current locale; $0 preserves leading/trailing spaces. See the gawk manual for string/length behavior: gawk manual.

If you want in-place editing and a backup, Perl is convenient and gives precise control (and can be made Unicode-aware):

perl -i.bak -pe 'chomp; $_ .= "foo foo\n" unless length($_) == 4000' file.txt

This creates file.txt.bak first; adjust encoding handling if you need true Unicode codepoint counts. See Perl run options: perlrun.

Quick checklist missed in the thread:

  • If you keep the shell loop, use IFS= read -r line to preserve whitespace/backslashes.
  • Avoid unquoted echo $var (use printf '%s\n' "$var" or the streaming tools above).
  • Test on a sample and keep a backup before overwriting the original file.
  • Decide whether you need byte counts or character counts (multibyte encodings require locale/Unicode-aware tools).

Recommended Answers

All 5 Replies

Member Avatar for eggi

Hey there,

Just FYI - it's good to put what you've tried in your post, so everyone doesn't think you're doing homework ;)

You can write this all on one line if you want - use expr to count the chars on each line of the file

#!/bin/sh

while read x
do
        chars=`expr "$x" : '.*'`
        if [ $chars -eq 4000 ]
        then
                echo "${x}foofoo" >>tmpfile
        else
                echo ${x} >>tmpfile
        fi
done <inputfile

cp inputfile inputfile.bak
mv tmpfile inputfile

Hope that helps :)

, Mike

Member Avatar for seemit

This probably is bettre approach. Worked for me

while read line
do
if [[ ${#line} -eq 4000 ]]
         then echo ${line}| tee -a out.txt
else echo ${line}"foofoo"| tee -a out.txt
fi 
done < inputFile.txt
Edited by Dani because: Formatting fixed
Member Avatar for seemit

Thanks anyway Eggi.. and ermm.. was'nt doing homework.. its monkey work.

Member Avatar for eggi

No offense meant,

I've just been warned against answering questions every once and a while when no proof of work was given in the post - just giving you a heads up since you had 0 posts :)

, Mike

Member Avatar for seemit

No offense meant,

I've just been warned against answering questions every once and a while when no proof of work was given in the post - just giving you a heads up since you had 0 posts :)

, Mike

Thanks Mike. Will keep that in my script.

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.